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CHAPTER 2

LITERATURE REVIEW AND OBJECTIVES

2.1 Introduction

In the recent past, the demand for diesel engines has increased rapidly. This is

mainly because of their higher thermal efficiency, better performance and reliability.

In the earlier days diesel engines were considered to be high pollutants than petrol

engines. But with the continuous improvements in the technology, there is a

considerable reduction in the emission levels in diesel engines. Still the research

works are continuing to bring down the levels of emissions; simultaneously the efforts

are continuing in the direction of improving the overall engine performance. In DI

diesel engines the fuel is injected directly into the combustion chamber. Here the

piston crown is a part of the combustion chamber. Fuel atomization, vaporization and

mixing of fuel and air occurs in a rapid sequence within the combustion chamber in

the fraction of a second. This can be achieved with the following: good combustion

chamber, appropriate in-cylinder air motion and fuel injection arrangement. Swirl is

mainly used for getting the adequate fuel- air mixing rates. Air swirl is generated with

the support of a suitable inlet port and it is amplified at the end of the compression

stroke by forcing the air towards the cylinder axis into the bowl-in-piston combustion

chamber. Swirl is basically an organized rotation of air about the cylinder axis.

Though some decay of swirl occurs due to presence of friction during the cycle,

intake generated swirl persists throughout the compression process as well as in the

combustion and expansion processes. The nature of the swirling flow in an actual

engine is extremely difficult to determine. Accordingly, steady state tests are often

used to characterize the swirl. Swirl ratio is defined as the solid-body rotating flow,

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which has equal angular momentum to the actual flow, divided by crankshaft angular

speed.

The diesel engine combustion is heterogeneous in nature. An improvement in

the combustion process definitely increases its efficiency and reduces the pollutant

formation. Better understanding of the engine in-cylinder fluid dynamics, fuel spray

behaviour, induction generated swirl and the combustion will definitely be helpful in

meeting the great challenges such as fuel economy and pollutant formation. The

sprays and combustion phenomenon in DI diesel engines have been highly influenced

by the induction generated swirl and the number of holes present in the nozzle. Hence,

critical review of the available literature related to the in-cylinder flows, fuel spray

characteristics, induction generated swirls and multi-hole nozzle are presented in the

following section.

2.2 Fluid flows in I.C. engines

Fluid dynamics is a field of science which studies the physical laws governing

the flow of fluids under various conditions. Computational fluid dynamics is used to

generate flow simulations with the help of computers. CFD involves the solution of

the governing laws of fluid dynamics numerically. The complex set of partial

differential equations is solved in geometrical domain divided into small volumes,

commonly known as a mesh or grid. CFD has enabled us to understand the

happenings in the world in new ways. CFD enables analysts to simulate and

understand fluid flows without the help of instruments for measuring various flow

variables at desired locations.

The internal combustion Engine flow modeling is one of the most

challenging fluid dynamics problem, as it is associated with the compressible flow,

density variations, turbulent, cyclic with spatial and temporal perceptions etc.,. The

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combustion phenomenon is greatly influenced by the fuel-air mixture formation and

the distribution of fuel within the combustion cylinder.

Pearson et al., (1990) [1] have reported computationally efficient simulation

technique. This technique is based on the linearised one-dimensional conservation

equations. These equations are suitable for distributed parameter systems and are

suitable to the requirements of the designer in assessing the relative merits among

different types of manifold configurations. Volumetric efficiencies of measured and

predicted are compared to understand the importance of variable geometry induction

systems.

Aita S et al., (1991) [2] have reported the analysis for the flow in an intake

port-valve-cylinder assembly of a DI diesel engine. The simulation was carried for

both steady state and transient motored situations during the suction and compression

strokes. Generation of angular momentum flux and the induced in-cylinder flow

motion were predicted for a helical port under steady state condition. The predicted

results were correlated and compared with the experimental results. The experimental

results were extracted with the support of oil film visualizations on valve and intake

port surfaces and attached with the local velocity measurements in the cylinder.

The transient flow simulations showed different characteristics of flow motion

in-cylinder and piston bowl during suction and compression processes. It was

reported that the swirl generating capacity of the valve is not the same during the

periods of valve opening and closing. A strong interaction was observed between the

swirling motion and the position & shape of the piston bowl.

Sweetland et al., (1994) [3] have used particle image velocimetry (PIV) to extract

gas velocity and turbulence in a diesel engine. Experiments were conducted on a

single-cylinder caterpillar engine. Optical access was provided for the combustion

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chamber. The results obtained for the turbulent jet were compared with that of earlier

results obtained through other techniques. The estimates of the turbulence intensity

are obtained from PIV data. The length scales are estimated from the model relations

of k-ε and the turbulent dissipation. The size of vorticity concentrations and the eddies

that are obtained from PIV are reported to be the representatives of the turbulence

integral length scale. The experimental results were also compared with the results

obtained from multidimensional KIVA-3 code. The experimental and the predicted

results are observed to be in good agreement.

Sebastian et al., (1995) [4] have simulated a production engine at part and full

load conditions. Modified engine was analyzed at full load. SPEED CFD code was

used for the analysis. The fuel-air mixing and combustion process are visualized with

the support of the iso-surfaces of stoichiometric mixture. The correlation of this

surface with global quantities such as heat release, pressure, temperature and swirl

ratio was considered. The global properties that are presented here are resolved for

the main chamber and the swirl chamber separately. The formation of thermal NO

and soot are simulated and analyzed.

Kang et al., (1995) [5] have performed in-cylinder flow simulations. KIVA-3

code was used for the analysis. The valve flow conditions that were measured from

the experiments was used as an inflow boundary conditions. The predicted swirl

ratios in a steady flow environment were compared with the swirl ratios of an

operating engine. Some differences were noticed in 3-D flow structures between a

steady flow environment and the operating engine. Axial development of the flow

produced an organized swirl in the case of a steady flow rig. Whereas merging of

multiple swirls and tumble motion were observed in the case of an operating engine.

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Landress et al., ( 1996) [6] have used the KIVA-3 CFD code to simulate the

flow through the port and the engine cylinder. From the results it was reported that,

mixing of the intake and residual gases is not uniform. Many complex flow structure

developments are happening during intake and they are getting destroyed during

compression. The flow field near TDC exhibits spatial in homogeneities in

temperature, kinetic energy and its dissipation rate.

Taylor et al., (1997) [7] have developed a computational methodology (3D

model) for predicting the losses in the intake regions of IC engines. In order to get

accurate results, the following tasks were implemented in the present methodology,

they are: (i) appropriate modelling of flow physics, (ii) quality of the geometry,

(iii) discretization schemes applied at low viscosity regions and (iv) turbulence of

higher order. This methodology was tested and validated against the data of a variety

of complex 2D and 3D laminar and turbulent flow conditions. The predicted pressure

losses in the intake region of a caterpillar diesel engine are compared with the

experimental data. The analysis was carried out in detail that could describe the

locations of the loss pockets that are associated mechanisms which are contributing

for the losses and the other sources for the losses. Simulations were carried out for

large scale, viscous and for all the turbulent flow situations. From the results it was

observed that there is good agreement between the predicted and the measured values.

Fuchs et al., (1998) [8] have simulated the suction, compression and

combustion processes of a caterpillar diesel engine. KIVA-3 CFD code was used for

the analysis. Seven variations on intake and two injection schemes were considered

during the study. From the results it is observed that, the combustion and emission

behaviour was influenced by one of the following three factors i.e., swirl ratio,

temperature and turbulence.

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Barths et al., (1998) [9] have studied the comprehensive chemical

mechanisms. This includes all the relevant chemical combustion processes that take

place in a DI diesel engine during auto-ignition, the burnout in the partially premixed

phase, diffusive burning and formation of pollutants. The complete structure of the

flame is preserved without simplifying highly nonlinear dependencies of the

chemistry. Using the representative interactive flamelet model the one-dimensional

unsteady set of partial differential equations is solved online with the 3-D CFD code.

Applying this model pollutant formation in acetane fuelled Volkswagen DI 1900

diesel engine was investigated. It was shown that the soot emissions are primarily

controlled by the mixing process in the cylinder. Numerical simulations for different

injection rates are compared with in house experiments.

Chen et al., (1998) [10] have simulated the engine flow with the support of a

STAR-CD CFD code. Simulation was performed for the inlet port and combustion

chamber flow fields. Volkswagen DI diesel engine having two-valves was used for

the study. The predicted results were compared with the results that are obtained from

laser-doppler anemometer measurements. The results were extracted and compared

for the three periods: valve opening, valve closing and maximum valve lift periods.

The results that are predicted for different engine speeds are validated against the

measured data. The accuracy of the predictions are reported.

Okazaki et al., (1999) [11] have studied exclusively on the design of intake

and combustion systems. Computational fluid dynamics approach was used for the

study. Main attention was on the correlation of the trapping efficiency and the swirl

ratio. The data that was obtained from the engine operation and the steady flow rig

tests were combined in the process of quality improvement. The requirements of the

designers as well as the researchers were satisfied.

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Baby et al., (1997) [12] have carried out an experimental investigation on in-

cylinder motion, during the intake and compression strokes of a multi-valve engine.

Experiments were conducted on a single cylinder four valve research engine. The

engine was attached with several optical accesses on cylinder liner and cylinder head.

laser doppler velocimetry was used for the measurement of the turbulence and local

velocity in combustion chamber. Effects of different bowl shapes on turbulence, flow

variations, and tumble distortion were analysed. Study was extended to evaluate the

effect of bowl location on the tumble charge angular momentum.

Shenghua et al., (1999) [13] have developed a model based on the Hiroyasu's

multi zone combustion model. Nozzle injection (spray) parameters, induction swirl,

air and fuel composition was considered in the model. Sub models pertaining to zone

velocity, air entrainment rate, droplet evaporation rate, combustion rate etc., were

taken from the latest literature. The model simulation was used to extract the

parameters like cylinder pressure, heat release rate and emissions (NOx and soot). The

predicted results of zone velocity and spray tip penetration are compared with the

predictions that are reported by Hiroyasu. The predicted results showed good

agreement with the experimental data.

Chiu (2000) [14] has consolidated the theoretical accomplishments in droplets

and sprays in the twentieth century, with an emphasis on the evolution of scientific

concepts, paradigms and methodologies. A structural spray theory, which was

developed form an early view of isolated droplets, has evolved in to a new view that

the interaction droplet and micro-scale structures and clusters of many-systems are

also fundamental entities in practical sprays. Outstanding issues and critical

bottlenecks that have prevented further advancement of the existing analytical theory

of droplet physics are examined, and an emerging research trend in a unified theory of

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droplet phenomena was discussed. Recent accomplishments and future prospects of a

unified theory are presented to coupling the status of this special branch of droplet

science and its future application.

Randall et al., (2005) [15] have studied numerically the quasi-steady

vaporization and combustion of multiple-droplet arrays. Vaporization rates, shapes of

the flame surface and flame locations were found for different fuels and droplet array

configurations. The number of droplets, the droplet arrangement within the arrays

and the droplet spacing within the arrays are varied to determine the effects of these

parameters. It is reported that the droplet interactions, the number of droplets and

relative droplet spacing will affect significantly the vaporization rate of droplets

within the array and consequently the flame shape and its location are also affected.

For small droplet spacing, the droplet vaporization rate decreases below that obtained

for an isolated droplet by several orders of magnitude. Similarity parameter, which

correlates vaporization rates with array size and spacing was reported. Individual

droplet flames, internal group combustion, and external group combustion were

reported that they are depending on the boundary conditions and droplet geometry.

Anand Kumar et al., (2005) [16] have used KIVA CFD code to analyze the in-

cylinder flow of a four stroke gas engine. The simulation results were compared with

the available experimental results. The effect of different motoring speeds on the

intake-generated turbulence, mass flow rate, velocity, swirl ratio and TKE were

analyzed.

Alfred et al., (2005) [17] have investigated the influence of in-cylinder swirl

patterns along the axis of the cylinder that are obtained during compression on flow

velocities and generated TKE at TDC. In-cylinder flow velocity field is predicted

during induction and compression periods. The analysis was carried out using multi-

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dimensional modeling. It is observed that the swirl ratio, swirl located near the piston

surface at early compression resulted in higher magnitudes of TKE and swirl inside

the bowl.

Kuleshov (2005) [18] has developed a model that deals with the diesel sprays

and combustion. Submodels that are capable to predict the emissions like NO and soot

have been implemented in the model. The model was used to handle the parameters

like injection strategies, injection direction, swirl intensity, droplet size and the bowl

shape. Inorder to predict the appropriate evaporation rates, nusselt number for the

diffusion process, pressure and temperatures were used. There was observed a good

agreement between the experimental and the predicted results.

Ravindra Aglave (2007) [19] has used KIVA III CFD code. A modified k-

model was used for in-cylinder turbulence. Discrete droplet model was used along

with the sub-models to predict collision, breakup and evaporation. There was

observed establishment of the suitability of intrinsic low-dimensional manifold in

simulations. Their simulation was considering turbulence-chemistry interactions using

a presumed PDF approach with greater accuracy in predicting kinetically controlled

process.

Janakiraman et al., (2007) [20] have presented the importance of combustion

process and stated that the rise in pressure was controlled by combustion process. And

the combustion process in turn was controlled by parameters like injection timing,

compression ratio etc., The parameters like pressure, emissions such as CO, CO2,

NOx, HC and soot against crank angle that are measured from the experiments.

Artificial neural networks technique was used for developing correlations. For this

purpose a feed forward back propagation neural network is used. The network is

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optimized by varying the number of hidden layers, number of hidden layer neurons,

activation functions and training algorithms.

Pacaud et al., (2009) [21] have worked with HSDI diesel engine on the

following areas: (i) conducting tests at low temperatures (ii) CFD analysis for cold

start operation. The results that are obtained from the tests are conducted at low

compression ratios were compared with the tests of normal compression ratios. From

this comparison it was stated that the delay can be reduced significantly in the case of

a low compression ratio when compared with that of normal compression ratio case.

In addition both the simulation and experimental analysis were carried out in cold

ambient conditions. Correlations between experiments and predictions gave consistent

explanations justifying cold start mechanisms and first order phenomena concerning

to vaporization and combustion.

Errico et al., (2007) [22] have analyzed two different approaches on

complexities associated with diesel combustion. The analysis was carried out with the

support of an open source code called open FOAM. This model was having the sub-

models namely: the eddy dissipation model and the partially stirred reactor model and

models related to emissions. The predicted results especially the cylinder pressure and

the pollutant concentrations were compared with the experimental results.

Liang et al., (2010) [23] have aimed at reducing the gap between the detailed

chemistry associated with the hydrocarbon fuel combustion and the predictions from

computational fluid dynamics. The techniques that were included in the present study

are a surrogate blend optimizer and a guided mechanism reduction methodology. New

methods for coupling the pre-reduced kinetic models accurately with the

multidimensional transport equations were also included in the methodology. The

new methods include the algorithms pertaining to dynamic adaptive chemistry (DAC)

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and dynamic cell clustering (DCC). These techniques are demonstrated by

determining a multi-component diesel fuel surrogate mechanism, reducing it as

appropriate for the conditions of interest, and then employing the reduced mechanism

in a multidimensional CFD calculation of diesel engine combustion. The CFD

simulation employs the newly developed FORTÉ simulation package, which was

designed to take advantage of the advanced chemistry solver methodologies as well as

advanced spray models. It was proved that the demonstrated techniques are highly

efficient and accurate.

Musu et al., (2010) [24] have introduced a new concept to control the HCCI

combustion. This was called as homogeneous charge progressive combustion

(HCPC). Here while the combustor piston moves in the downward direction the

compressor piston moves in the upward direction. Because of this the air was with the

compressor admitted to the combustor cylinder. At the same time the fuel was

injected into the transfer duct. Fuel evaporates and mixes with the air that brings the

conditions needed for homogeneous combustion. A detailed CFD study was carried

out on a new turbocharged HCPC engine and obtained clean combustion.

Wickman (2003) [25] has optimized the combustion chamber geometry design

of a HSDI diesel engine, for which KIVA-GA code was used. The optimum split-

spray piston design was demonstrated experimentally. This design was proved to be

able to achieve low emissions when using retarded injection timing, high swirl ratio,

high injection pressure, high boost pressure, high EGR rate, and a low compression

ratio.

Hideyuki et al., (2000) [26] have analyzed the fuel spray distribution in a DI

diesel engine. They used pilot and main fuel injections at different piston positions to

prevent the main fuel injection from hitting the pilot flame. From the CFD analysis it

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is observed that the movement of the piston with a cavity divided by a central lip

along the center of the sidewall effectively separates the cores of the pilot and main

fuel sprays. Experiments showed that an ordinary cavity without the central lip

emitted increased the smoke. whereas smokeless, low NOx operation was realized

with a cavity divided by a central lip even at heavy loads.

Li et al., (2000) [27] have conducted CFD simulations to investigate the

combustion in a direct-inject (DI) diesel engine using the Ricardo engine CFD

program VECTIS and the Ricardo two-zone flamelet (RTZF) combustion model. The

simulation program covered full load and part load operating conditions, each

including 6 to 7 cases. CFD simulation results were compared against engine tests for

the in-cylinder pressures and NOx emissions. The comparison shows that the RTZF

combustion model performs well in all cases studied with no tuning of model

coefficients necessary. The detailed time history of spray, fuel distribution and flame

development obtained from the CFD simulation is proved to be an useful information

towards gaining a better understanding of the features of combustion in DI diesel

engines.

Bo et al., (2009) [28] have presented the CFD simulation that was performed

on a 4-cylinder in-line diesel engine. VECTIS CFD code was used for the study.

The simulation was run through multiple cycles and covered the intake, compression,

spray, combustion and exhaust processes. The simulation was run through multiple

cycles. The converged solution was compared with the engine test data for cylinder

pressure, charge distribution and EGR distribution.

Claywell et al., (2006) [29] have investigated on the intake design to gain

further insight into the nature of the airflow. Intake designs were classified with

reference to the physical layout. Then Ricardo software WAVE (1D) and VECTIS

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(3D) were used to investigate the performance of the three most common intake

concepts as well as two variations of the base concepts for a naturally aspirated four-

cylinder Formula SAE engine. Simulations were carried out at three rpm using

WAVE and VECTIS coupled at the intake inlet and runner exits of each intake

concept. A 3D simplified CAD geometry of each intake was used for the VECTIS

part of the simulation. An unsteady flow analysis was used instead of a steady flow

analysis due to the nature of the flow within an engine. Intake performance is

determined by several factors: cylinder-to-cylinder volumetric efficiency, time of

choked flow in the restrictor, total pressure loss along the restrictor, sound spectrum

frequency content, and physical packaging characteristics. In addition, intake

manifold and restrictor interaction was discussed. Adverse flow conditions are

visualized. Packaging considerations such as the location of flow bends for minimum

pressure loss were also discussed. It was stated that the conical-spline intake concept

showed the best performance.

Li (2010) [30] has presented the latest development of his work on multiple-

cylinder engine CFD simulation using Ricardo's engine-focused commercial CFD

code, VECTIS. The detailed chemistry-based Ignition progress variable library (IPV-

library) approach was used for combustion modeling. The simulation was carried out

on a 4-cylinder in-line diesel engine. The converged solution was compared to the

engine test data. It was proved that with a detailed chemistry-based combustion

modelling scheme, the approach was having the capability to cover a broader range of

operating conditions and also different types of engine combustion. Additionally, in

terms of computational cost, the use of a combustion reaction library in the

framework of cell-based CFD analysis ensured great efficiency. It has been

demonstrated that multiple-cylinder engine CFD simulation with detailed chemistry-

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based combustion modeling can be achieved with VECTIS on an affordable time

scale and computational cost.

Kini et al., (2008) [31] have made detailed study on the conventional mesh

generators. The CAD surface data available for mesh generation is far from

satisfactory for volume mesh creation. Dissatisfactions include no node-to-node

matching between mating parts, minute gaps, overlapping surfaces, overlapping parts,

etc. To clean up this kind of data to a level that can be used for volume mesh creation

requires a lot of manual work that could take a couple of weeks or more. The new

model that was developed presented a fast and fully automated, Cartesian cell

dominated projected mesh generation algorithm used in CFD-VisCART that

eliminated the need for CAD data cleaning, thus shaving off weeks worth of time off

the design cycle. This process of mesh generation involved the volume mesh cells

being generated first and then projected onto the surfaces of the CAD model in order

to create the surface mesh automatically. Additionally, the projection method has

intrinsic advantages when dealing with minute gaps and overlapping parts. Shrink-

wrapping (to cover up larger holes or simplify an assembly of parts), automatic hole

detection (to detect any mesh leaks), gap handling (to ensure proper mesh resolution

between neighboring parts) and such other tools together with the novel features of

the projection algorithm mentioned here have reduced the turnaround time for mesh

generation from 3–4 weeks to less than one day.

Golovitchev et al., (2000) [32] have proposed a new methodology that

coupled the generalized partially stirred reactor (PaSR) model with that of highly

efficient numeric to treat detailed oxidation kinetics of hydrocarbon fuels. In this

approach, chemical processes were assumed to proceed in two successive steps they

are: (1) the reaction follows after the micro-mixing is completed on a sub-grid scale,

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(2) experimental observations on soot formation. KIVA-3 code was used to run the

simulation. The model was used to simulate the turbocharged Volvo DI diesel

engines. It was observed that the soot reduction effect attributed to a shortening of

fuel injection duration.

2.3 Literature on Spray Characteristics

Bo et al., (1997) [33] have used SPEED CFD code for the study. Three-

dimensional model was used for predicting the gas motion and spray characteristics.

Analysis was carried out on a small HSDI diesel engine. The complexities associated

to the engine geometry were included in the model by considering the implicit finite

volume method along with the unstructured mesh. Various sub models are also

incorporated for the model. The predicted results were compared with the results

obtained from LDA measurements, in particular the velocity field during the

induction and compression to the extent of ignition. Quantitative measurements of

spray penetration and local droplet velocities are reported to be in agreement.

Moon et al., (2007) [34] have made an attempt to investigate the spray

characteristics of a swirl injector for a direct injection spark ignition engines. A highly

inclined nozzle was used for the test. The obtained results were compared with the

conventional and the L-stip nozzle. An open hollow cone spray is observed for the 700

taper angle. The taper angle should be optimized to avoid the formation of rich areas

and to increase the spray volume. Improvement in the atomization was observed for a

high fuel temperature injection.

Hannouny et al., (2003) [35] have conducted an experimental and numerical

characterization. It was conducted for high-pressure fuel injection systems. One single

and one double guided multi-hole and valve-covered-orifice type of injector was used

with a common rail system. Mini-sac injectors two in numbers are used for hydraulic

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electronic unit injection system (HEUI) with different orifice diameters. They have

made an extensive study on the effect of injection system and the operating conditions

on the emissions of a small HSDI diesel engine. A high-speed digital camera was

used to extract the images of the transient sprays. These images were used to obtain

spray tip penetration and cone angles. The droplet sizes averaged over the entire spray

(SMD) were extracted from the images using the light extinction method (LEM). The

KIVA code and the engine emissions measurements are used to correlate the spray

characteristics and the emissions, NOx and soot. The results emphasized the

correlation between the spray behavior and the emissions.

Schmidt et al., (2002) [36] have used the number time counter for droplet

collision algorithm with an embedded collision mesh. It was observed that this change

was able to reduce the grid dependency. The grid dependency was further reduced

with the support of a noval interpolation scheme that transforms the velocities into

polar components before doing interpolation. There was observed a considerable

decrease in grid dependency. All these changes have reduced the uncertainity in

droplet size and improved the spray penetration consistency.

Mohammadi et al., (1998) [37] have developed a single nano-spark back light

photography method in order to record the image of non-evaporating diesel sprays.

Diesel was injected into a high pressure nitrogen gas. From these images a clear

image of fine droplets and spray was obtained. In order to quantify the droplet

characteristics such as, droplet size and shape an image analysis method was

developed and implemented. Double-nano spark photography of diesel sprays was

carried out and relatively clear double exposure images of droplets were obtained on

the same film. Two dimensional size and velocity measurement of droplets were

simultaneously carried out based on these photographs. Distribution of droplets

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velocity was clarified and used to describe the droplets distribution. The measurement

of two-dimensional velocity of ambient gas was done using a particle tracking

velocimetry (PTV) method.

Zhu et al., (2000) [38] have developed and presented A methodology for

coupling the fuel injection system and its effect on spray characteristics. The method

was applied to a case of a conventional pump-line-nozzle system. Mathematical

models that characterizes the flows from the pump to the nozzle are formulated and

solved using the method of characteristics and finite difference techniques. The nozzle

internal flow was modeled using zero-dimensional flow models, in which the nozzle

cavitation and its effect on the nozzle exit flow were taken into account. The models

are validated with available experimental data. The interaction between the upstream

flow and the nozzle flow, as well as the effects of nozzle flow on the spray

characteristics at the nozzle exit are predicted and analyzed.

Chang et al., (1997) [39] have investigated the effects of fuel viscosity and

also the effects of nozzle inlet configuration on the spray characteristics. Three

different viscosity fuels were used in the study. Two mini-sac six hole nozzles with

different inlet configurations were used. Spray was introduced into a constant volume

chamber using a common rail injector system. A high speed movie camera

synchronized with a pulsed copper vapor laser was used to capture the images of high

pressure transient sprays. The images were analyzed to obtain the spray tip

penetration and the spray cone angle at two regions. Overall SMD was calculated with

light extinction method.

Francisco et al., (1999) [40] have presented a model that deals with the

atomization and evaporation of transient sprays. The model was associated with the

following sub-models namely primary atomization, droplet evaporation and droplet

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deceleration. The experimental data was extracted from the engine which was

equipped with a two component phase-doppler anemometer. The 3D fluid mechanics

code (PHONICS) was used for predicting the spray.

Jung et al., (2001) [41] have proposed a hybrid model that consists of

modified Taylor analogy break up (TAB) model and discrete vortex method (DVM).

The simulation process was divided into three steps. The first step was analyzing the

breakup of droplet of injected fuel using modified TAB model. The second step was

based on the theory of sieber liquid length. The liquid length analysis of injected fuel

was used for connecting both modified TAB model and DVM. The third step was to

reproduce the ambient gas flow and inner vortex flow injected fuel by using DVM. In

order to examine the hybrid model, experimental study was done on a free

evaporating fuel spray at early injection stage of in-cylinder like conditions. The

numerical results are compared with the experimental ones. The calculated results on

gas jet flow by DVM quantitatively in agreement with the experimental results

especially for the downstream of evaporative spray.

Xiaofeng et al., (2000) [42] have developed a relative velocity correction

model (RVC), combined with the drop tracing system and spherical coordinate

transformation that can work for a 3D case. The new model was implemented in

KIVA-3V code. The calculated results were compared with the experimental data for

both single-hole and three-hole fuel injections, including the spray tip penetrations

and the spray images. The comparison shows that the RVC model performed well for

all the cases.

Patterson et al., (1998) [43] have developed a new spray model to improve the

prediction of diesel engine combustion and emissions. The KIVA-II CFD code was

used for the analysis. The accuracy of modeling the spray breakup process was

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improved by the inclusion of Rayleigh-Taylor accelerative instabilities, which are

calculated simultaneously with a Kelvin-Helmholtz wave model. This model

improved the prediction of the droplet sizes within a diesel spray and provided a more

accurate initial condition for the evaporation, combustion, and emissions models. An

improved droplet drag model was presented. The improved model accounts for the

increased droplet drag. This was due to the change in the droplet's shape and the

increased frontal area of the droplet. The drag model locally affects the breakup

process and produced a more realistic droplet size distribution. It was reported that it

was highly accurate while performing the vaporization process calculations. This

model was used for the prediction of pressure, heat release, and emissions produced

by single and split injection. New model was capable to predict the results accurately.

Allocca et al., (1992) [44] have studied on a non-evaporating transient high

pressure diesel spray operating under different ambient conditions. Tip penetration

and sauter mean diameter (SMD) were measured using the high speed photography

and the laser light extinction techniques. The simulations were carried out using

KIVA-II code with and without breakup sub-model. The effect of the grid spacing on

the numerical results was also evaluated. The KIVA –II simulations were

underestimating the jet penetrations. The SMDs that are obtained from simulations are

in disagreement with the experiments. The atomization model and the experimental

limitations were showed as the major reasons for the inaccuracies.

Xu et al., (1992) [45] have investigated the discharge coefficients of the

needle-seat opening passage and discharge hole in orifice-type diesel nozzles. Simple

empirical correlations were obtained between these coefficients and needle lift. These

relations were used while calculating the injection pressure. Based on the calculated

transient injection pressure, spray tip penetration was calculated by taking the overall

25

line which covers the trajectories of all fuel elements ejected during the injection

period. The results obtained from the calculations are validated by comparing them

with the results obtained from the wide range of experiments.

Arrègle et al., (1999) [46] have characterized the macro and microscopic

behaviour of diesel sprays generated by a common-rail system. The influence of

injection parameters and boundary conditions was quantified through a detailed

experimental study. The main purpose of this research was to validate and extend the

different correlations available in the literature pertaining to sprays generated by

common-rail systems, i.e., at high injection pressures with small nozzle holes. The

sprays are characterized in an environment which simulates the in-cylinder air density

existing in the real engine when the injection starts. A wide parametric study has

generated the data. This data was used to quantify the influence of the common-rail

pressure, nozzle hole diameter and gas density on the following: (i) spray tip

penetration, (ii) spray cone angle, (iii) geometric volume of the spray, (iv) spatial and

temporal evolution of drop size distribution. The results obtained from the theoretical

analysis are compared with the experimental results.

Stanislav Danov et al., (1999) [47] have developed a mathematical model of

combustion process in a diesel engine based on the theory of the chain reactions for

the higher hydrocarbon compounds. The rates of fuel vaporization and combustion are

defined by the instant values of temperature, pressure, concentration of fuel vapors,

overall diffusion rate, fuel injection rate, and mean fuel droplet size (SMD).

Numerical experiments have been carried out for investigating the interdependencies

between various combustion-related parameters. In specific, the effect of SMD on the

subsequent combustion parameters, such as, pressure, temperature, thermodynamic

properties of air/gas mixture, heat transfer, fuel vaporization, combustion rate, current

26

A/F ratio, gas mixture composition have been investigated. In addition, the integral

indicator parameters of the engine, such as the mean indicated pressure, peak

pressure, compression pressure have been analyzed.

Bianchi et al., (1999) [48] have presented a hybrid model. Their model was

capable to describe both primary and secondary breakup of high-dense high-pressure

sprays. They used the model proposed that was proposed by Huh and Gosman. Huh et

al., model was to compute the atomization of the liquid jet (primary breakup). The

TAB model of O'Rourke and Amsden was used to estimate the secondary breakup.

The atomization model considers the jet turbulence at the nozzle exit. The model also

considers the growth of unstable wave on the jet surface. Hybrid model was validated

against a free non-evaporating high-pressure-driven spray at engine like conditions.

The breakup time evaluation accuracy was improved by tuning the TAB

constant Ck. In the later part, sensitivity analysis of the grid resolution was carried out.

They found that the cell sizes used in common I.C. engine computations are not

sufficient to resolve the transient diesel-spray accurately. Influence of the turbulence

dispersion model on spray structure was discussed and introduced a new one.

Salah Addin et al., (2000) [49] have investigated on the impact of two models

representing two limiting cases of the droplet heat-up process. They are (i) infinite

diffusivity (ID) and (ii) diffusion limit (DL) model. These models work on the

evaporation, self-ignition and subsequent combustion in a diesel spray. The

simulation results showed that, when compared with the DL model, the ID model lead

to an over-prediction of the ignition delay by about 20%. This is attributed mainly to

the under-prediction of the evaporated mass predicted in the case of the ID model,

during the early stages after injection. The time evolution of the combustion processes

in the case of the ID model is observed to lag that was predicted with the DL.

27

Desantes et al., (2007) [50] have developed a model that simulates the diesel

spray dynamic behaviour. As a result of a theoretical reasoning based on momentum

flux conservation in the axial direction of the diesel spray, a mathematical model

which relates the momentum flux with profiles of velocity and concentration was

obtained. The new model was developed by considering the local density variations

and the deduction of the model for a generic schmidt number. A PDPA system and

additional measurements of spray momentum, mass flow rate and spray cone angle

were used in order to validate the model in high density environment and real

injection pressure conditions.

Bykov et al., (2007) [51] have developed a new decomposition technique for a

system of ordinary differential equations. It is based on the geometrical version of the

integral manifold method. The solution was obtained by comparing the values of the

right hand side of these equations, leading to the separation of the equations into ‘fast’

and ‘slow’ variables. The hierarchy of the decomposition was allowed to vary with

time. Equations for fast variables are solved by a stiff ODE system solver with the

slow variables taken at the beginning of the time step. The solution of the equations

for the slow variables was presented in a simplified form, assuming linearised

variation of these variables for the known time evolution of the fast variables. This

can be considered as the first order approximation for the fast manifold. This

technique was applied to analyze the explosion of a polydisperse spray of diesel fuel.

Clear cut advantages are demonstrated from the point of view of accuracy and CPU

efficiency when compared with the conventional approach widely used in CFD codes.

The difference between the solution of the full system of equations and the solution of

the decomposed system of equations was shown to be negligibly small for practical

28

applications. It was observed that in some of the cases the system of fast equations

was reduced to a single equation.

Sung et al., (2006) [52] have made an experimental study on the microscopic

and macroscopic breakup characteristics. Study also deals with the velocity and size

distributions of mono-dispersed droplets in relation to the breakup regimes. The

engine was provided a droplet generator equipped with a piezo stack produced mono-

dispersed droplets. The droplet-breakup phenomenon was captured in microscopic

and macroscopic views by using a spark lamp, a Nd-YAG laser, a long distance

microscope and a CCD camera as a function of the weber number. Along with the

analysis of the images, the droplet size and velocity distributions were measured in

the near nozzle region by a phase doppler particle analyzer system. It was showing the

size and velocity distributions of disintegrated droplets at the bag, stretching and

thinning, and catastrophic breakup regimes. In the bag breakup regime, the droplets

separated into small and large droplets during breakup. Alternatively, the droplets

disintegrated at a shorter duration and formed a cloud, similar to a fuel spray injected

through an injector, in those regimes.

Choongsik Bae et al., (2000) [53] have investigated the spray characteristics

from different holes of VCO (valve covered orifice) nozzles was performed and its

results were compared to standard sac nozzle. The global characteristics of spray,

including spray angle, spray tip penetration, and spray pattern were measured from

the spray images which were frozen by an instantaneous photography. A spark light

source and ICCD were used for the purpose. These spray images were acquired

sequentially from the first injection to fifth injection to investigate injection to

injection variation. For better understanding of spray development and their internal

structures, a long-distance microscope was used to get magnified spray images at the

29

vicinity of the nozzle hole with a laser sheet illumination. Also backward illuminated

images with a spark light source were taken to understand surface structures of dense

spray from VCO nozzle of common-rail injection system.

Laguitton et al., (2002) [54] have described how two high-speed video

cameras were utilised to achieve the pseudo 3-D imaging of the spray and of auto-

ignition sites. The usage of schlieren imaging that enabled vapour phase analysis was

also described. New correlations were established for the liquid and vapour

penetrations and the vapour phases. Attempts were continued by reducing the size of

the injector orifice. An experimental correlation against in-cylinder density for auto-

ignition delay was presented. An increased charge density reduced the penetration

where as it reduced the auto-ignition delay.

Sudhakar Das et al., (2003) [55] have reported the simulation of an outward

opening injector. The analysis was carried out using the modified KIVA-3V code.

The modified injection model was validated with the experimental data. The effect of

computational grid resolution was also reported. Using the validated code, a

parametric study of the effect of nozzle exit diameter, tangential velocity at the nozzle

exit and stream wise velocity on the injector characteristics such as spray penetration,

sauter mean diameter (SMD), and volume distribution (DV90) was carried out. A

strong effect of the tangential component of velocity (swirl) at the nozzle exit was

observed on the scattering (spread) of spray droplets.

Desantes et al., (2006) [56] have conducted research on the diesel spray

injected into chamber having stagnant ambient air. The investigation was continued

with an aim to perform an in-depth analysis on the influence of injection parameters

on the spray dynamics and spray macroscopic characteristics. As a result of

theoretical approach that is based on momentum flux conservation along the spray

30

axis. Model which predicts the spray axis velocity and spray tip penetration was

obtained. Measurements of momentum flux and spray cone angle are needed in order

to predict axis velocity and spray penetration. The chamber density was assumed to be

constant and equal to the density of the pressurized air inside the chamber. A

Gaussian radial profile was assumed for the axial velocity. Experimental results from

a conventional common rail injection system with five axi-symmetric nozzles were

obtained. Tests were carried out for a wide range of injection pressures and densities

to obtain additional information of the model and also for the validation purpose.

These experimental results include a large number of momentum fluxes (impact

force), spray tip penetration and spray cone angle measurements.

2.4 Literature on Swirl

Heywood (1988) [57] has stated that in medium and small DI diesel engines

swirl is used to attain adequate fuel- air mixing rates. Air swirl is generated by

adopting suitable changes in the design of inlet port. Friction at the cylinder wall

surfaces and the turbulent dissipation of the fluid tries to reduce the angular

momentum of the air entering during induction and the same is continued while the

compression process is in progress. Swirl velocity can be increased by adopting

suitable changes in the combustion chamber design.

Ferguson et al., (2004) [58] have tried to present the effect of design changes

on the moment of inertia. They could show that the swirl is proportional to angular

momentum and is inversely proportional to the moment of inertia. The bowl-in-

pistons increases the swirl. Increased swirl is observed to be reducing the moment of

inertia as the piston approaches TDC. It is found that, during compression as the

piston approaches TDC the swirl increases and starts decreasing after TDC more or

less with the same pace.

31

McCracken et al., (2001) [59] have proved that the optimal swirl level changes

as the geometry of the bowl-in-piston changes. Two different bowl-in-piston

combustion chambers were taken into account. Both the bowls were tested for the

same swirl levels. The trends are observed to be the same for both the bowl

geometries. There was observed quantitative differences in the air fuel mixing rate.

The turbulence generated by the jet is also influencing the air-fuel mixing rate.

Fuchs et al., (1998) [60] in their work it has been showed that, the use of bowl

in-piston chamber effects the in-cylinder motions. The high swirl ratios may distribute

the fuel such that it remains in the bowl. This gives a great scope to deplete almost all

of the bowl oxygen during combustion. It has produced stratification of the fuel and

air, and poor late diffusion burn.

Takahashi et al., (1987) [61] have considered different types of combustion

chambers in order to understand the influence of geometry on in-cylinder swirl. It was

observed that the combustion chamber of square type created turbulence at each

corner of the combustion chamber. The turbulence and swirl together contributed for

the enhancement of the air-fuel mixing rate. A flange lip was provided at the entrance

of the square type combustion chamber in order to increase air turbulence. Proper care

was taken to ensure that this turbulence is not permitted to penetrate the area of fuel

spray. It is observed that the lip-type of combustion chamber with high swirl might

affect the cold start. Certain modifications are essential to handle these situations.

They stated that the DI diesel engine performance is influenced by air swirl.

At low engine speeds adopting an air inlet port with high swirl ratio can improve

smoke levels and fuel consumption. But at high engine speeds high swirl port reduces

air flow co-efficient, that lowered the volumetric efficiency but it reduced the

combustion efficiency and the pumping losses were increased. It was suggested that

32

adopting a low swirl inlet port might overcome this situation. But at low engine

speeds and at low inlet swirl increased the smoke levels. In order to maintain the

appropriate fuel air ratios attempts were made by varying the swirl ratio to improve

the fuel consumption and to reduce the smoke levels. This was achieved by

introducing a sub port type variable swirl system in addition to the main inlet port.

Shimada et al., (1986) [62] have made attempts to develop a variable swirl

inlet system with the support of a developed swirl control sub port. Attempts were

made to control the angular momentum of the inlet flow into the cylinder. This

variable swirl system was used to investigate the effects of swirl on direct injection

diesel engine performance and emissions. It was observed that the lower swirl level

reduces the rate of initial stage burning that effects the NOx emission, maximum

cylinder pressure and the rate of cylinder pressure. Same is observed to happen over

the entire range of engine speeds and loads. An improvement in the BSFC and

reduction in the NOx levels were achieved. An intercooled turbocharged engine was

fitted with variable swirl inlet system. There was observed higher low-speed torque,

higher brake horse power and improved cold start. It was also observed that the earlier

conclusions are majorly influenced by the selection of optimum swirl that suits the

engine.

Beard et al., (1998) [63] have conducted experiments on various bowl shapes

such as flat, w-shaped and with or without re-entrant. It is observed that the shape of

the piston bowl is an important parameter to control the turbulence level and fuel air

mixing rates. A small change in the bowl shape has influenced the flow parameters

like swirl numbers and or turbulence intensity. This in turn modifies the combustion

efficiency. It was reported that in the re-entrant region of the w-bowl shape both the

33

swirl and the turbulence level increased at around TDC position when compared with

flat bowl piston.

Takabayashi et al., (2005) [64] have contributed for the development of

Honda accord 1.8 litre lean burn VTECH engine. This engine was analyzed using

Ricardo VECTIS. RTZF combustion model was used for simulating the combustion

process. The results showed that the analysis for both steady and unsteady in-cylinder

calculations is in good agreement with the earlier works. The intake port and piston

crown were optimized to improve the lean burn of air fuel ratio.

Li et al., (2006) [65] have conducted CFD simulations on a DI diesel engine

using Ricardo VECTIS software. It reports that the Ricardo two-zone flamelet

(RTZF) combustion model was used for analysis. Analysis was carried out on a small

HSDI research engine. The simulation continued for 6 cases forming a complete

injection time swing. The results predicted using the RTZF combustion model are in

good agreement with the experimental results.

Stone et al., (1992) [66] have tried to establish the significance of axial swirl

in diesel engines, and proved that the axial swirl is used in medium and small DI

diesel engines for improving the fuel and air mixture rate. Axial swirl contributes for

the generation of turbulence with the aid of interaction of the tangential velocity

because of the inward flow produced by the squish region. The presence of swirl takes

care of the cycle-by-cycle variation in the mean flow. This in turn controls the cycle-

by-cycle variation in combustion.

Dae Choi et al., (2004) [67] have made an attempt to measure the gas velocity

and multi-dimensional numerical simulation. This data was used for the evolution of

the structure of the turbulent flow within the cylinder. The study was carried out on a

bowl-in-piston engine of re-entrant type. The parameters that are contributing to

34

produce the turbulent energy are correlated and compared. The developed model was

assessed using the experimental data. It has been proved that the isotropic portion of

the normal stresses is the main source of turbulent energy for low swirl ratios. This

proved to be significant for all the swirl ratios. At higher swirl ratios the mean swirl

velocity is predominant at TDC. Squish contribution for the generation of turbulence

is due to the swirl velocity distribution. Increased swirl and the spatial distribution of

swirl velocity is appeared to be the effective method to increase the chamber

turbulence. The simulated mean flow fields are in good agreement with the measured.

Miles et al., (2003) [68] have made an attempt to measure both the radial and

the tangential velocity components in a HSDI diesel engine. Three different swirl

ratios and four injection pressures were taken into account. The study was made in the

absence of combustion. Length scales were estimated through Taylor’s hypothesis.

KIVA-3 code with the RNG k-ε turbulence model was used. The simulated and

experimental results indicated that the fuel injection event is the major source of late-

cycle turbulence and the flow structure can be a major source of turbulence at high

swirl ratios.

Magnus Sjoberg (2001) [69] have made an attempt to modify the fuel injector,

such that the fuel may be made to rotate around its axis. This is done to attain

sweeping injections. The sweeping injection enhances the air entrainment into the

spray. This is observed to be the reason for the reduced smoke level. The normal and

non-sweeping injection tends to build up fuel pockets, and the sprays hits the walls of

the piston bowl. Increasing the swirl ratio from 1.65 to 2.47 was not reducing spray

impingement onto the bowl wall impact. Reduction in the smoke levels are attained as

the swirl ratios were increased. It is found that the counter-swirl rotation of the

injector was reducing the impact onto the bowl wall. This has increased the

35

combustion rate and reduced the smoke levels. The fuel close to the bowl wall burns

slowly that raised the soot levels.

Dembinski et al., (2012) [70] have made an experimental investigation on

spray and mixture formation in a CI engine. An optical engine fitted with a high-

speed digital camera was used. Spray and mixture formation was varied by varying

the swirl, tumble and the injection pressure. Change in the swirl ratio was achieved by

changing the designs of the inlet port, the valve seat masking and the injection

pressure. This was attained by varying the designs of inlet port. In order to evaluate

the combustion process particle image velocimetry software was used. Images of soot

particles were also captured. The experimental results are observed to be well in

agreement with the simulation results. It was observed that the induced swirl was

surviving for the compression and combustion periods, where as the tumble was not

surviving up to the late combustion. The angular velocity is observed to be higher

close to the centre and reduces to the lowest at the outer piston bowl edge. An

increase in the injection pressure increases the deviation from solid body rotation.

Michal Dyer (1979) [71] have conducted experiments to validate computer

models of IC engine combustion. Tests were carried for a set of well characterized

and extensively varied experimental conditions, in order to evaluate the codes

pertaining to kinetics and fluid mechanics. In order to measure the thermodynamic

properties, the engine was attached with laser doppler velocimetry, pressure sensors

and thermocouples. High speed laser shadowgraph filming, laser Rayleigh scattering

and laser refraction techniques were used in the combustion diagnostic process.

Thermodynamic properties of the swirling, uniform pre-combustion mixture

are characterized by measuring pressure, temperature distribution, velocity/turbulence

36

and equivalence ratio. Experiments were carried out on a combustion bomb. The

experimental results were used to validate the computer code.

Gunasekaran et al., (2011) [72] have worked with engines that are arranged

with the shrouds on the intake valves in order to achieve air guided mixture

preparations. In this process, three types of flow structures were considered. They are

low tumble, high tumble and swirl. From the results it is observed that, the high

tumble with late injection provided a better mixture distribution.

Charton et al., (1996) [73] have studied experimentally and numerically on the

combustion of a swirling, stoichiometric and homogeneous mixture. Mixture contains

natural gas and air in a short cylinder. Swirl was induced by rotating a disc. In the

process of varying swirl intensities and turbulence, discs having varied roughnesses

and different disc speeds were considered. By doing so the effect of turbulence and

the induced swirl on combustion were studied. Pressure plot was used to examine the

combustion rates. In order to understand the effect of swirl on flame high speed

schlieren photography was used. It was observed that an increase in swirl intensity

initially reduced the burning span and on further rise in swirl intensity increased the

burning duration.

Vinay Nagaraju et al., (2009) [74] have made an attempt to investigate

experimentally on the effect of swirl ratio and injection pressure of a HSDI diesel

engine. The engine was equipped with a turbo charging facility, a swirl control

mechanism, common rail injection system and an EGR system. A blend of biodiesel

and low sulphur diesel fuel was used for the study. In order to understand the

combustible mixture formation and the auto ignition process the heat release rate was

taken into account.

37

Neal et al., (2012) [75] have made an attempt to study the effect of swirl ratio

on combustion in an optically-accessible diesel engine. Detailed study was made on

extended lift off combustion (ELOC). This is different from traditional combustion.

ELOC resulted in reduced soot levels. In order to visualize the impact of swirl ratio on

combustion, a High-speed imaging of OH chemiluminescence and natural luminosity

were used. Higher swirl ratios have showed longer curved path for the jets.

Ladommatos et al., (1992) [76] have described the three linked computational

models. These models are used for the estimation of the following; (i) swirl generated

during the induction process, (ii) changes in swirl in the case of a bowl-in-piston

combustion chambers during compression while the piston approaches top dead

centre (iii) the interaction of the fuel sprays with swirl, that includes the relative

crosswind velocities between the air and the fuel sprays and also the velocities during

spray impingement. Experimental results were extracted from a single-cylinder DI

diesel engine. Study was carried out by altering both the fuel spray and swirl

parameters systematically. The predicted spray impingement and crosswind velocities

are correlated with the results obtained from experiments. The comparison in

particular was for fuel economy and smoke emission.

Benny Paul and V. Ganesan (2010) [77] have studied on the effect of different

manifold configurations on air motion and turbulence inside a DI diesel engine. The

different manifold congurations such as, helical, spiral, and helical-spiral

combinations are considered here. GAMBIT was used for meshing the 3D model.

STAR-CD CFD code was used to predict the flow characteristics of these models.

The predicted results of swirl velocity at different locations at the end of compression

stroke are compared with the experimental results of the available literature. The

results obtained for helical manifold model showed reasonably good agreement with

38

the measured data given in the literature. RNG k-ε turbulence model was used. The

helical-spiral manifold is observed to give maximum swirl ratio inside the cylinder

than helical manifold.

Shenghua et al., (1999) [78] have developed a new swirl generator to induce

the induction swirl in the cylinder. In this process a short straight port swirl generator

was developed. The swirl generator was having several curvilinear diversion blades

and it was installed at the inlet valve. It is observed that, with the support of different

swirl generators it is possible to generate vary the generated swirl strengths within the

engine. Controlling the airflow rate it is showed that it is possible to generate variable

swirl. Engine tests proved that variably induced swirl has a considerable influence on

diesel engine fuel consumption.

2.5 Literature on Number of Nozzle Orifices

Campanella et al., (1994) [79] have carried out studies on a standard five-hole

V.C.O. nozzle of D.I diesel engine. Several pictures of the spray were taken using the

back-light photography technique. Injected volume, feeding pressure, injection

duration, spray penetration, angle and thickness, and flash delay from the start of

injection were measured both for nozzles of two different manufacturers and for a

group of four injectors before and after a fatigue test of about 1500 hours of running.

Measurements revealed that each spray strongly depends on the needle lift, the back-

pressure and the nozzle geometry. The causes of the most important differences have

been attributed at the different holes inclination, their asymmetric feeding conditions

(due to the eccentricity between needle and nozzle) and the micro defects caused by

drilling operation.

Das et al., (2009) [80] have described a correlation study on fuel spray pattern

recognition of multi-hole injectors for gasoline direct injection (GDI) engines. Spray

39

pattern is characterized by penetration length, which represents the distance of

maximum droplet concentration from the axis of the injector. Five fuel injectors with

different numbers and sizes of nozzle holes were considered in this study.

Experimental data and CFD modelling results were used separately to develop

regression models for spray patternation. These regressions predicted the influence of

a number of injector operating and design parameters, including injection system

operating pressure, valve lift, injector hole length-to-diameter ratio (l/d) and the

orientation of the injector hole. The regression correlations provided a good fit with

both experimental and CFD spray simulation results. Thus CFD offers a good

complement to experimental validation during development efforts to meet a desired

injector spray pattern.

Giorgio et al., (1995) [81] have studied on the spray of a 5-hole, VCO nozzle

for D.I. diesel engines. The data was obtained from each hole and are compared. A

high pressure injection system (elasis patent), electronically controlled, was used. To

investigate the behaviour of each hole a “cap” was used to cover the nozzle in such a

way that only one hole at a time could inject in the spray chamber. The investigation

consisted of a photographic characterization with back-light technique and of the

droplet size distribution through laser diffraction technique via Malvern. Four

pressure values (30, 60, 90, 120 MPa) and three injected flow rates (10, 25, 40

mm3/inj.) were chosen to characterize the behaviour of the nozzle. Each test was

carried out with the nozzle under normal running conditions, measuring the laser

signal background after each acquisition. The influence of the injection frequency, of

the number of the injections needed before running conditions, of the background

measurement and data acquisition were investigated. The investigation revealed that

the presence of an internal part of the spray made of drops of smaller diameter. The

40

different value of droplet size distribution in sprays, obtained from different holes but

working under the same conditions, have been attributed to the different hole

inclinations in respect to the injector axis. More inclined holes produced sprays of

droplet of bigger diameter.

Malbec et al., (2010) [82] have investigated on the air entrainment of multi-

hole Diesel injection using high speed particle image velocimetry (PIV). A multi hole

common rail injector with an injection pressure of 100MPa was used for the study.

The sprays are observed in a high pressure, high temperature cell that reproduces the

thermodynamic conditions which exist in the combustion chamber of a diesel engine

during injection. Typical ambient temperature of 800K and ambient density of

25kg/m3 are chosen. The air entrainment was studied with the PIV technique, giving

access to the velocity fields in the surrounding air and/or in the interior of two

neighboring jets. High acquisition rate of 5000 Hz, corresponding to 200 µs between

two consecutive image pairs was obtained by a high-speed camera coupled with a

high-speed Nd-YLF laser. The effect of neighbouring jets interaction was studied by

comparing four injectors with different numbers of holes (4, 6, 8 and 12) with similar

static mass flow rate per hole. The results show that both the maximum air

entrainment level and the total mass of entrained air are similar for all the injectors,

and therefore are not affected by neighboring jets in the conditions studied. However

the transient behavior of the air entrainment process is affected when the number of

holes is high, hence when two neighboring jets are near (12 holes nozzle): the air

entrainment reaches a maximum at later timings compared to the other nozzles. An

analysis of the velocity fields between the two jets shows that this result might be due

to the air flow inertia generated when the two jets are near. The transient behaviour

after the end of injection (EOI) was also studied using the 4-holes injector. The results

41

showed a very rapid decrease of the mean axial velocity near the nozzle after the EOI.

The air entrainment becomes maximum at a given position and this position

propagates downstream towards the jet tip.

Matthias et al., (2012) [83] have demonstrated collaborative 3D-CFD and

experimental efforts, majorly focused on optimizing the mixture stratification and the

potential for high engine efficiency with low NOx emissions. Performance of the

hydrogen engine was evaluated over a speed range from 1000 to 3000 rpm and a load

range from 1.7 to 14.3 bar BMEP.

Engine maps showed that the hydrogen direct injection engine operating above

35% brake thermal efficiency (BTE) over approximately 80% of the tested operating

range. A more detailed characterization of engine efficiency is done by quantifying

the effects of different loss mechanisms in the engine at relevant points throughout the

engine map. The dominant loss mechanism was heat loss to the combustion chamber

walls and as a function of both engine speed and load. There exists a trade-off

between wall heat losses and other partial losses. As a result, the peak BTE was

observed at 2000 rpm, 13.5 bars BMEP.

A series of engine maps showed efficiency improvements due to optimal

injection timing and also showed efficiency and NOx improvements due to injector

nozzle design. The most promising engine configuration uses a 4-hole nozzle which

showed improvement over the previous 5-hole nozzle. The final engine map showed a

peak BTE of 45.5% and part-load BTE of 33.3%, demonstrating the ability of the

hydrogen direct injection engine to exceed both U.S. DOE light-duty efficiency

targets. The 4-hole nozzle also provides a mixture that is less potent for NOx than the

5-hole nozzle which correlates to a significant decrease in NOx emissions at the peak

42

efficiency operating point. The corresponding map of NOx emissions was dominated

by less than 0.10 g/kwh of NOx.

Scarcelli et al., (2011) [84] have described the validation of a CFD code for

mixture preparation in a direct injection hydrogen-fueled engine. The cylinder

geometry is typical of passenger-car sized spark-ignited engines, with a centrally

located injector. A single-hole and a 13-hole nozzle are used at about 100 bar and 25

bar injection pressure. Numerical results from the commercial code fluent (v6.3.35)

are compared to measurements in an optically accessible engine. Quantitative planar

laser-induced fluorescence provides phase-locked images of the fuel mole-fraction,

while single-cycle visualization of the early jet penetration was achieved by a high-

speed schlieren technique. The characteristics of the computational grids are

discussed, especially for the near-nozzle region, where the jets are under-expanded.

Simulation of injection from the single-hole nozzle yields good agreement

between numerical and optical results in terms of jet penetration and overall

evolution. The 13-hole nozzle creates intense jet-to-jet interaction, with all jets

merging into a single effective jet immediately downstream of the under-expanded

region. This phenomenon (usually referred as coanda effect) is more challenging to

the numerical simulation and requires higher level of details in numerical simulation

and grid resolution, with particular regard to the fields near the injector nozzle.

Montgomery et al., (1996) [85] have conducted an experimental study on the

performance and emissions of an engine. Series of experiments were conducted on a

constant volume cold spray chamber. The investigation was carried out with a goal of

exploring the effects of number of holes and size on the emissions and performance of

a DI heavy duty diesel engine. The spray experiments provided insight into the spray

parameters and their role in the engine's combustion processes.

43

The fuel system used for both the engine and spray chamber experiments was

an electronically controlled, common rail injector. The injector nozzle hole size and

number combinations used in the experiments included 225X8 (225 gm diameter

holes with 8 holes in the nozzle), 260X6, 260X8, and 30OX6.

The engine tests were conducted on an instrumented single cylinder version of

the caterpillar 3400 series heavy duty diesel engine. Data was taken with the engine

running at 1600 RPM, 75% load. Engine emissions and performance results include

oxide of nitrogen emissions (NOx), particulate emissions, and brake specific fuel

consumption (BSFC). NOx versus particulate trade-off curves were generated over a

range of injection timings for each nozzle. The pressurized spray chamber was used in

the room temperature spray visualization experiments. Results of the image analysis

that give spray tip penetration length, spray cone angle, and droplet size are presented.

Inorder to understand the effect of nozzle geometry, computer modeling of the engine

was prepared. The KIVA-II code was used to model the combustion with the different

injector nozzle geometries. The results of the modeling effort emphasize the

importance of the details of the spray on diesel engine emissions.

Jung et al., (2011) [86] have implemented the Premixed compression ignition

(PCI) combustion using advanced injection strategy and exhaust gas recirculation in a

DI diesel engine single cylinder. The injection timing swept experiment using a

baseline injector, which had an injection angle of 146° and 8 nozzle holes, obtained

three types of combustion regime: conventional diesel combustion for an injection

timing of 10° CA (crank angle) BTDC (before top dead center), PCI combustion for

an injection timing of 40° CA BTDC and homogeneous charge compression ignition

(HCCI) combustion for an injection timing of 80° CA BTDC. The burn duration,

which was defined as the period from 10% to 90% of the accumulated heat release,

44

was very short in PCI combustion but not in the others. PCI combustion with an

injection timing of 40° CA BTDC was achieved in a range of an exhaust gas

recirculation (EGR) rate from 0% to around 40%.

Two types of different injectors were applied to investigate the effect of

injection angle and the number of nozzle holes on PCI combustion: one had an

injection angle of 70° and 8 nozzle holes, the other had an injection angle of 70° and

14 nozzle holes. These two injectors could implement PCI combustion as well. The

indicated mean effective pressure (IMEP) for both injectors with a narrow injection

angle (70°) was higher than that for the baseline injector because the injected fuel

could be direct toward the piston bowl so that most of the fuel could participate in the

combustion. The IMEP for the injector with 8 nozzle holes was higher than that for

the injector with 14 nozzle holes. On the other hand, when the injection angle was

70°, the injector with 14 nozzle holes had low levels of HC and CO emissions

because of better air utilization compared with the injector with 8 nozzle holes, which

was supported by a spray cone angle analysis. A maximum pressure rise rate (MPRR)

analysis showed that the MPRR for PCI combustion was higher than that for

conventional diesel combustion and HCCI combustion. The MPRR for the injectors

of a narrow injection angle in PCI combustion was higher than that for a baseline

injector. However, for the injectors of a narrow injection angle, there was no

difference in the MPRR of PCI combustion with respect to the number of nozzle

holes.

Kilic et al., (2006) [87] have evaluated the injection nozzles. A measuring

adapter for the determination of the injection quantities for individual spray hole was

developed. They stated that with the measuring adapter it is possible to determine the

jet flow injection quantities that were influenced by the variation in shape and the

45

geometry of the individual nozzle components. The measurements are reported to be

supported by simulation results. The spray hole shape was crucial for flow coefficient

and cavitation in the spray hole.

During fuel atomization the diameter and shape of the injecting holes and the

pattern realized by the nozzle needle in addition to the injection pressure play a

substantial role. Here was asserted that the smaller the spray hole diameter, the larger

the mass flow difference between the individual spray holes due to the increase in

variation in the manufacturing process. Macro- and micro-geometrical structure of the

spray hole surface and the transient areas of the nozzle interior into the spray hole has

a strong influence on the flow conditions within the range (area) of the nozzle needle

seat and within the spray holes and thus on flow values, flow symmetry and

cavitation. The cavitations starts earlier at higher inclination angles (that means the

flow is deflected more) and lower pressure differences.

Design parameters like the angle at which the individual spray hole comes off

the nozzle tip (inclination-angle), as well as manufacturing process driven parameters,

such as the shape of the spray hole inlet edge (grinding radius) influenced the quantity

of fuel flowing through the individual spray hole. The mass flow variability was

reduced by grinding the spray hole either for nozzle to nozzle or for spray hole to

spray hole.

Wehrfritz A et al., (2011) [88] have studied numerically the influence of the

number of fuel sprays in a single-cylinder diesel engine on mixing and combustion.

The CFD simulations were carried out for a heavy-duty diesel engine with an 8 holes

injector in the standard configuration. The fuel spray mass-flow rate was obtained

from 1D-simulations and was adjusted according to the number of nozzle holes to

keep the total injected fuel mass constant. Two cases concerning the modified mass-

46

flow rate are studied. In the first case the injection time was decreased whereas in the

second case the nozzle hole diameter was decreased. In both cases the nozzle holes

(i.e. fuel sprays) was increased in several steps to 18 holes. Quantitative analyses were

performed for the local air-fuel ratio, homogeneity of mixture distribution, heat

release rate and the resulting in-cylinder pressure. The results showed that an

increased number of fuel sprays leads to a more homogeneous fuel distribution, but

also to a more incomplete combustion.

Arcoumanis et al., (2000) [89] have made attempts to provide better

understanding on the cavitating flow characteristics in large scale nozzles. A six-hole

conical sac-type nozzle provided with a quartz window in one of the injection holes

has been used to visualize the flow under cavitating flow conditions. Simultaneous

variation of both the injection and the back chamber pressures were allowed. Images

are obtained at various cavitation and reynolds numbers for two different fixed needle

lifts corresponding to the first- and the second-stage lift of two-stage injectors. The

flow visualization system was based on a fast and high resolution CCD camera

equipped with high magnification lenses which allowed details of the various flow

regimes formed inside the injection hole to be identified. From the obtained images

hole cavitation initiated at the top inlet corner of the hole was identified. The string

cavitation formed inside the sac volume and entering into the hole from the bottom

corner, was also identified. Comparison of the cavitation images obtained in the real

size nozzle with those obtained in an enlarged fully transparent acrylic nozzle replica

has confirmed that similar flow regimes may form inside the injection hole of real size

and large scale injectors. Despite the similarity in the macroscopic cavitation

structures that were found to depend on cavitation intensity, the transient development

of cavitation bubbles was identified to be different inside the two nozzles due to the

47

different residence and life time of the moving bubbles. Based on the flow similarity

between the real size and enlarged multi-hole nozzles and previous extensive

experience on the cavitating flow characteristics in large scale nozzles, better

understanding of the cavitating flow in real size nozzles operating under Diesel engine

conditions has been obtained, which can guide the development of relevant computer

models.

Skogsberg et al., (2005) [90] have investigated on the ways of improving the

spray formation from spray-guided multi-hole gasoline direct injection injectors.

Work was carried out both experimentally using laser diagnostic tools and

numerically using computational fluid dynamics. Laser induced exciplex fluorescence

(LIEF) measurements in a constant pressure spray chamber and optical engine

measurements have showed that the injectors with 6-hole nozzles and 50-degree

umbrella angles are unsuitable for stratified combustion because they produce steep

air-fuel ratio gradients and create a spray with overly-deep liquid fuel penetration as

well as presence of liquid fuel around the spark plug. In order to study the injector

performance, numerical calculations using the AVL FIRE™ CFD code was used. The

numerical results indicated that, increasing the injector umbrella angle, the extent of

piston wall wetting can be decreased. Also, changing the pattern of holes in the nozzle

changes the spray pattern, enabling its optimization with respect to ignition and flame

propagation.

Furthermore, PDA and direct imaging experiments showed that increasing the

l/d ratio by reducing the hole diameter resulted in a decrease in the mean droplet sizes

(D32). The spray angle was found to increase with decreasing l/d ratios. It was

reported that by choosing a suitable l/d ratio, it is possible to control the local AFR

and cross-flow velocity at the spark plug.

48

Blessing et al., (2003) [91] have developed methods for analysing the effect of

individual nozzle configuration parameters on the fuel atomization and the fuel spray

propagation. These are observed to affect the raw emissions of NOx and soot in

modern DI diesel engines, apart from the fuel injection rate, atomization of the liquid

jet and mixing of the fuel with the combustion air. Optical diagnostics and CFD

methods were developed at the Daimler chrysler research. These methods are

combined with an analysis of the injection system hydraulics and are linked to a

detailed analysis of mixture formation and combustion inside an optically accessible

engine. The first part of the paper, methods for the experimental investigation with

transparent 1 and 6 holes nozzles in real size geometries under high pressure

conditions are described. Special emphasis was put on CFD methods for modeling the

cavitating two phase nozzle flow. In the second part the processes occurring in a sac

hole nozzle of a common rail injector during the complete injection event are

discussed. The influences of the spray hole position, inlet rounding and conical shape

of the spray hole are presented. Finally a comparison between a needle lift controlled

(CR=common rail) and a pressure controlled (PLN=pump line nozzle) injection

system was made.

Arcoumanis et al., (1999) [92] have used a one-dimensional, transient and

compressible flow model to simulate the flow and pressure distribution in advanced

high-pressure fuel injection systems; these include electronic distributor-type pumps

with either axial or radial plungers and a common-rail system. Experimental data for

the line pressure, needle lift, injection rate and total fuel injection quantity obtained

over a wide range of operating conditions (from idle to high speed/full load) were

used to validate the model. The FIE system used for validation comprised an

49

electronic high-pressure pump connected to two-stage injectors of different type

including 6 hole vertical and 5 hole inclined conical-sac and VCO nozzles.

A number of important parameters: (i) the injection pressure at the nozzle tip,

(ii) the effective hole area at the hole exit due to the presence of hole cavitation, (iii)

the fuel injection temperature, (iv) the hole-to-hole variability of inclined nozzles,

were predicted for three high pressure fuel injection systems. These parameters are

varied for different nozzles. It was shown that all important nozzle exit conditions for

the control of the subsequent spray development are strongly dependent on the

detailed geometric and operating characteristics of the injection system. It was

facilitated in the computer models.

Hottenbach et al., (2009) [93] have designed a new injection system for DI

Diesel engines to decrease the soot emissions. A nozzle with clustered holes was

observed to be a promising approach to minimize soot production. The basic idea of

the cluster configuration (CC) nozzles was to prevent a fuel rich area in the center of

the flame where most of the soot was produced, and to minimize the overall soot

formation. For this purpose each hole of a standard nozzle was replaced by two

smaller holes. The diameter of the smaller holes was chosen such that the flow rate of

all nozzles was equal. The basic strategy of the cluster nozzles was to provide a better

primary break up and therefore a better mixture formation caused by the smaller

nozzle holes. Three possible arrangements of the clustered holes were investigated.

Both the cluster angle and the orientation to the injector axis are varied. The common

rail diesel injector was installed in a combustion vessel, in order to provide nearly

quiescent high-pressure and high-temperature conditions.

The combustion and soot formation are analyzed using three different

measurement techniques. The hot reaction zone was visualized using OH*

50

chemiluminescence imaging which occurs during the second stage ignition. The local

soot concentration during combustion was measured semi-quantitatively using laser

induced incandescence (LII). In both measurements the soot luminosity was recorded

simultaneously using a second camera or a double frame camera, respectively. The

soot formation was discussed for all nozzles. The data indicated that soot formation

can be reduced using cluster nozzles under these conditions.

Brands et al., (2012) [94] have attempted to characterize the mixture

formation in the sprays emanating from multi-layer (ML) nozzles under

approximately engine-like conditions by quantitative, spatially, and temporally

resolved fuel-air ratio and temperature measurements. ML nozzles are cluster nozzles

which have more than one circle of orifices. They were introduced previously, in

order to overcome the limitations of conventional nozzles. In particular, the ML

design yield the potential of variable spray interaction, so that mixture formation

could be controlled according to the operating condition. In general, it was also a

primary aim of the cluster-nozzle concepts to combine the enhanced atomization and

pre-mixing of small nozzle holes with the longer spray penetration lengths of large

holes. The applied diagnostic, which was based on 1-d spontaneous Raman scattering,

yields the quantitative stoichiometric ratio and the temperature in the vapor phase.

The measurements are conducted in non-reacting sprays. It was established that the

stoichiometric ratio in the region of flame lift-off significantly affects the soot

formation in diesel sprays. The measurements are conducted in a high-temperature,

high-pressure vessel. N-decane is used as the fuel, because it was a commonly applied

model fuel for diesel. The investigated diesel-like sprays emanate from a state-of-the-

art piezo injector.

51

The results of two ML nozzles with two circles of orifices were compared.

The plane of the two holes in each cluster was parallel to the injector axis. The

clustered nozzle holes are convergent (−4°) for one of the ML nozzles, whereas they

are divergent (+4°) for the other one. Two conventional nozzles with one circle of

orifices are also investigated, one with the same flow number as the ML nozzles and

the other one with halved flow number, corresponding to a single hole of the ML

nozzles. The temporal and spatial evolution of the quantitative stoichiometric ratio

and temperature was determined and discussed. Further, the shot-to-shot variability in

these quantities are analyzed. These measurements showed that the ensemble-

averaged fuel-air-ratio distributions are very similar for both ML nozzles and the

reference nozzle with large orifices, but they are significantly different for the

reference nozzle with small orifices. The shot-to-shot variability in the fuel-air ratio

are generally very similar for the ML nozzles as compared to a previously

investigated cluster nozzle with only one orifice circle, indicating that the particularly

complex in-nozzle flow does not lead to enhanced fluctuations of the outcome of the

mixture formation process. The results also lead to conclusions on soot formation in

comparable combusting sprays emanating from ML nozzles. Apparently, the soot-

reduction potential cannot be improved by enhancing evaporation and penetration of

the free spray simultaneously using an ML nozzle. Thus, previously observed reduced

engine-out soot emissions for ML nozzles could be explained by wall impingement or

differences in flame lift-off.

Bianchi et al., (2000) [95] have designed with a goal to improve the air-fuel

mixing and therefore they were characterized by the adoption of high-swirl ports and

re-entrant bowls. Experiments have shown that the high injection velocities induced

by common rail (CR) systems determine an enhancement of the air fuel mixing. CR

52

systems causes a strong wall impingement. The modification was aiming at exploiting

a new configuration of the combustion chamber more suited to CR injection systems

and characterized by low-swirl ports and larger bowl diameter in order to reduce the

wall impingement. The goal was to achieve a higher air flow rate during induction as

well as to reduce the fuel vapor wall impingement without compromising air-fuel

mixing efficiency. This new combustion chamber configuration has been tested

numerically and its performances have been compared to those of a HSDI four valve

diesel engine conventional combustion chamber. The analysis has been carried out by

using a customized version of the CFD code KIVA3. Experimental results of the

conventional engine have been used to validate the numerical models. The influence

of the injection system configuration (i.e, hole numbers, inclination of the spray axis

with respect cylinder head) on pressure cycle and NO x and soot engine-out emissions

has been analyzed too. Computational results seem to indicate that the new

combustion system concept may provide relevant benefits with respect to engine-out

emissions without reducing engine performance.

Gao et al., (2007) [96] have experimentally investigated the spray and

mixture properties of group-hole nozzle with close, parallel or a small included angle

orifices using the ultraviolet-visible laser absorption-scattering imaging technique, in

comparison with the conventional single-hole nozzle. The group-hole nozzle concept

is regarded as a promising approach to facilitate better fuel atomization and

evaporation for direct injection diesel engine applications. Three series of group-hole

nozzles were designed to investigate the effect of group-hole nozzle specification

while varying the included angle and interval between the orifices.

The results suggested that: 1) Group-hole nozzle with very close, parallel

orifices presents the similar spray characteristics with those of the single-hole nozzle.

53

However, with the increase of injection pressure, the group-hole nozzle shows the

potential to produce, to some extent, the better fuel atomization and evaporation

without adversely affecting the spray spatial distributions. 2) Increasing the diverging

angle between the orifices results in significant increase in mass of fuel vapor and

reduction in overall sauter mean diameter (SMD), indicating the evaporation

improvement. 3) In the case of group-hole nozzle with large interval between orifices

in this study, the restrained tip penetration, significant increase in the SMD, along

with large liquid phase mass appearance around the spray tip can be found, which is

considered to be a comprehensive result of the direct droplets collision in the

overlapping part of the two jets and the droplets overtaken and coalescence inside the

fuel spray due to the inferior spray tip penetration and ambient gas entrainment. 4)

The liquid mass proportion and the SMD of the fuel spray from all test group-hole

nozzles are greater than the estimated value by the LAS data of single-hole nozzle

whose orifice diameter is the same as one of the group orifices. Thus, the interaction

between the two jets has the effect of suppression of the ambient gas entrainment and

fuel evaporation, though it has the effect of enhancement of the spray tip penetration.

Tamaki et al., (2010) [97] have performed this study with an aim of improving

atomization characteristics and to obtain excellent spray characteristics with shorter

breakup length, larger spray angle and smaller droplet diameter. A high-efficiency

atomization enhancement nozzle, with large spray angle, short liquid core length and

small droplet diameter was obtained. Investigation was carried out on the atomization

of spray of the multi-hole atomization enhancement nozzle. The effects of dimensions

of the atomization enhancement nozzle such as hole number, the hole diameter,

position of the nozzle hole on atomization of the spray and atomization characteristics

were investigated. As a result, it was clarified that in case of the multi-hole

54

atomization enhancement nozzle with hole number of N=4, breakup length becomes

short about 70 p.c. and spray angle becomes large about two times, droplets of the

spray become considerably small compared with the single hole atomization

enhancement nozzle. Atomization characteristics were improved considerably and

uniform spray mass flux distributions are obtained by using the multi-hole

atomization enhancement nozzle with hole number of N=4.

Xuelong et al., (2011) [98] have proposed the study on a new low-temperature

premixed combustion mode to achieve the simultaneous reduction of NOx and soot

emissions in a volume production diesel engine of CA6DF by reconstructing key

systems. Some developments of this diesel engine are as follows. A straight port and

large diameter combustion chamber of a low compression ratio was developed. Inlet

ports of a high induction swirl ratio were developed. A cooled EGR was developed.

Especially, an ultra-multi hole (UMH) nozzle was developed. It has two layers of

injection holes and a large flow area. Two sprays of the upper and under layers meet

in the space of the combustion chamber. The results showed that the operation range

of this diesel engine to achieve the better low-temperature premixed combustion is as

follows. The speed can cover from the idle speed to the rated speed. The load can

reach to 50% of the full load of the corresponding external characteristics speed. The

NOx and soot emissions of this operation range are simultaneously largely reduced,

even by 80%–90% at most test cases, while keeping the brake-specific fuel

consumption (BSFC) from being significantly deteriorated.

Miao et al., (2009) [99] have stated that the lean premixed compression

ignition combustion provides the potential for simultaneous reduction of NO x and

PM, while imposing moderate penalties on CO and HC emissions. These drawbacks

were overcome in the existing premixed combustion modes of diesel engines using a

55

developed ultra multi hole nozzle. The UMH nozzle has two layers of injection holes

and a large flow area. Two sprays of the upper and lower layers meet in the space of

the combustion chamber. A high-pressure common-rail fuel injection system was

used in this experiment. The fuel injection rate of the UMH nozzle was measured

using the constant volume method, and its spray pattern was recorded using high-

speed digital photography. Combustion and performance experiments with the UMH

nozzle were conducted on a turbocharged intercooled diesel engine. The results

showed that the UMH nozzle exhibited a higher injection rate, shorter injection

duration, shorter spray penetration, and bigger spray angle than those of the

conventional nozzle. These characteristics facilitate better mixing of fuel and air prior

to ignition, and thus NO x and PM emissions were simultaneously reduced with low

CO and HC emissions by combining the UMH nozzle with EGR.

Dahlander et al., (2008) [100] have investigated the spray formation and spray

induced air movement associated with rotational symmetrical and asymmetrical

nozzle hole configurations. Four different nozzles with different hole configurations

and umbrella angle were investigated both experimentally and numerically in a

heated/ pressurized spray chamber. Their influence on spray formation, spray induced

air motion, cross-flow velocity, fuel/air ratio, turbulence and cycle-to-cycle variations

were studied. It was found that rotational symmetrical configurations produce non-

coherent isolated clouds of fuel. It was also found that an asymmetrical configuration

produces a coherent fuel cloud. All the nozzles tested produced partially premixed

vapor clouds, with cycle-to-cycle variations. Stated that these variations may be an

important issue for ignition stability in a closed-spaced combustion system.

Kim et al., (2009) [101] have investigated the spray characteristics of multi-

hole injectors with two different nozzle holes configurations for a gasoline direct

56

injection (GDI) engine according to the various injection conditions. Two GDI multi-

hole injectors with a different location and injection angle of six symmetric holes

located around the nozzle axis were used for this investigation on the spray

characteristics injected six individual plumes. The spray behaviors such as the spray

development process, the spray tip penetration from the nozzle tip, and spray cone

angle were analyzed from the spray images obtained by using the high speed camera.

Also, the local sauter mean diameter (SMD) according to the axial distance from the

nozzle tip and the overall SMD were measured by the droplet measuring system for

the comparison between atomization performances of two injectors. It was found that

the spray tip penetration and cone angle increase as the injection pressure increases. In

the comparison of results between two injectors, test injector with symmetric holes

positioned on the periphery of a larger imaginary circle than the other injector, shows

small values in the spray tip penetration and cone angle. In the atomization

characteristics, the local SMD makes difference according to the axial distance. The

effect of injection pressure on atomization of both sprays at the test injectors showed

that as the injection pressure increased, local and overall SMD show the decreasing

patterns.

George et al., (1998) [102] have adopted RNG model to perform computations

in realistic engine geometries. The parameters explored include the effects of piston

crown shape, injector targeting, glow-plug presence, injection velocity, injection

timing, number of injector holes and initial swirl ratio on mixing. It was concluded

that the mexican-hat design for piston enhances mixing due to the tumbling motion of

the mixture caused by that particular piston shape. The optimum injector hole angle

was found to be 450 with respect to the horizontal.

57

2.6 Literature on Injection Timing

Ergenc et al., (2012) [103] have stated that the quality of combustion majorly

depends on the formation of air-fuel mixture. They also stated that the mixture

formation primarily depends on various injection parameters. They have investigated

on the optimum injection advance angle for DI diesel engine. A single cylinder PLC

controlled DI diesel engine was used for this purpose. Diesel and diesel-ester blends

were used in their study. It was reported that at a particular injection advance peak

pressure occurred in less time, for ester blends.

Zhu Jianjun (2010) [104] has made an experimental analysis on a diesel

engine. Experiments were carried out for various conditions of fuel supply viz., angle

advancement and injection pressures. He has reported that NOx levels were decreased

in both the cases. He also stated that, there was noticed a small effect on Particulates.

Whereas there was no considerable influence on either CO or HC was observed.

Nwafor et al., (2008) [105] have made an experimental investigation on a

diesel engine. They have made an attempt to study the combustion behaviour by

advancing the injection. The tests were carried out on the same fashion for the fuels

viz., diesel and vegetable oil. The performance of the engine is reported to be smooth

at lower loads. They have also noticed that there was some reduction in the ignition

delay. Finally they could recommend the injection advancement for both the fuels.

Cenk Sayin et al., (2009) [106] have carried out experimental investigations

on a diesel engine using diesel fuel blended with ethanol. The experiments were

conducted at different injection timings, two of them fall into under advanced

injection timings and the other two fall into retarded injection timings. For all the

cases, ethanol blend percentage in the diesel fuel was up to 15%. From their study

they could conclude the following:(i)for the retarded injection timings: NOx, CO2 and

58

BSFC are increasing and BTE, CO & HC are decreasing, (ii) for the advanced

injection timings: NOx, CO2 have increased and CO, HC decreased, (iii) with regard

to the BSFC and BTE, better results were reported at the original injection timing.

Nwafor (1999) [107] has made experimental studies on a diesel engine using

natural gas. In this study, the injection timing was advanced and its effects were

observed. Because of this there was noticed a change in the ignition delay. They

proposed an appropriate injection timing at which the engine can run smoothly. They

also reported an increase in the fuel consumption at higher loads.

Kouremenos, et al., (2001) [108] have made both the theoretical and

experimental investigations on a DI diesel engine. Injection advancement was

considered as a major issue to analyse its impact on combustion and emissions. In

addition to that, EGR technique was implemented to control the levels of emissions.

From the study, a reasonable increase in peak pressure with the acceptable levels of

NOx was attained.

Jesus Benajes et al., (2001) [109] have studied on the changes that take place

in combustion and emissions while adopting pre and post injections. Single cylinder

diesel engine was considered for the study. In this process the quantity of fuel being

injected per cycle was also varied to understand its impact on combustion and levels

of emissions esp., NOx and Soot. Following are the major conclusions from their

study: (i) pre-injecting strategy - reduction in the fuel consumption with a penalty of

NOx and soot levels and (ii) post-injection strategy – reduction in the Soot levels with

a penalty of fuel consumption.

Hassan et al., (2011) [110] have experimentally investigated the effects of

advanced injection on an engine. A super charged dual fuel diesel engine was used for

this study. The main focus was on the engine performance and emissions. Injection

59

pressure was maintained to be same for all the cases under consideration. But the

injection flow rates of producer gas as well as the air were varied. The test was carried

out for different loading conditions against various speeds. They have finally

reported that, a considerable reduction in the levels of CO emission, Specific energy

consumption and increased Brake thermal efficiency were noticed.

Hassan et al., (2011) [111] have experimentally investigated on the engine

performance and emissions. They have tried to use the producer gas-diesel and

vegetable oil blends. Air and generated producer gas were injected into the intake

manifold. Injection timing of the pilot fuel was advanced. Experiments were

conducted for the following parameters viz., quantity of fuel, speed and load. It was

concluded that the performance of the engine with producer gas-diesel and vegetable

oil blends have come down. At rated loads the emissions are found to be increasing.

They have recommended the usage of vegetable oil as an alternative fuel for a

supercharged dual-fuel producer gas engine.

Zhixia et al., (2012) [112] carried out theoretical investigation on diesel

engine. They tried to vary the following parameters to study their influence on noise

and emissions: (i) pilot injection timing, (ii) quantity of fuel being injected and (iii)

the timing of main injection.

Yusheng Zhang et al., (2008) [113] have investigated the usage of DME as an

alternate fuel for a DI diesel engine. The following parameters were considered: (i)

engine load, (ii) fuel injection advancement, (iii) nozzle pressure, (iv) crank angle of

EVO and (v) DME. The influence of these parameters on the engine performance and

emissions were studied. DME fuelled engine was proved to be superior at an

appropriate nozzle pressure and fuel injection angle. By retarding the opening of

exhaust it was stated that NOx emissions have decreased.

60

Gorji et al., (2009) [114] have numerically investigated the combustion and

emission characteristics of a diesel engine. Their study majorly deals with the

injection strategies and intake conditions. Following are the parameters that were

taken into account: (i) spray cone angle, (ii) injection timing, (iii) intake temperatures

and (iv) multiple injections. They have noticed considerable changes in the Soot and

NOx formations among the considered cases. Following conclusions were reported:

(i) an increase in the injection angle increased the NO formation but decreased the

Soot levels, (ii) an increase in the cone angle increased the NO formation but no

change in the levels of Soot, (iii) as the injection timing was advanced resulted an

increase in the in-cylinder temperature, pressure and NO formation and reduced levels

of soot, (iv) an increase in the intake temperature resulted a rise in the NO formation

and (v) multiple injection reduced the formation of NO and Soot.

Usman Asad et al., (2009) [115] have carried out experimental investigations

for which a CR 4 cylinder diesel engine was used. The study was on the effects of fuel

injection strategies on the performance and emissions of a CR diesel engine. They

have concluded that, reduction in the levels of NOx and Soot are attainable. This

might lead to an increase in the levels of HC and CO.

Gunabalan et al., (2009) [116] have made attempts to investigate the effect of

early injection and EGR on engine performance and emission. Star-CD code was used

for this purpose. Following are the major conclusions: (i) with early injection and

without EGR – the occurrence of peak pressure has advanced and its value increased

and NOx levels have increased and Soot levels are decreased, (ii) with early

injection and with EGR – reduced the peak pressure, NOx and soot.

Sanghoon et al., (2008) [117] have made experimental investigations on a CI

constant volume vessel. Conditions that were maintained are more or less similar to

61

HCCI. Their attempt was mainly to identify the effect of fuel injection time on the

following: (i) air-fuel mixing, (ii) combustion and (iii) emissions. Electronic fuel

injection system was used to regulate the injection timings. They have noticed some

increase in the ignition delay. The contribution of this in the reduction of NOx is not

that considerable against the considered compression ratios and the engine speed. HC

and CO emissions were decreased noticeably. Whereas NOx has decreased. They

have also concluded that, to enhance the air-fuel mixture, the diesel spray should be

made to impinge near the bowl-lip area.

Suryawanshi et al., (2005) [118] have carried out experimental investigations

on a DI diesel engine. They have tried with an alternate fuel having the blends of

pongamia methyl ester with diesel. The tests were conducted at the standard and

retarded injection timings as well. Reduced levels of CO, HC and smoke was reported

with pongamia. Whereas very small rise in the levels of NOx was reported for normal

injection time. They reported similar behaviour with regard to brake thermal

efficiency and exhaust temperature.

Zhu et al., (2003) [119] have made a theoretical investigation on a CRDI.

They tried to find the extent by which injection timing, EGR etc., would influence the

engine performance and emission. KIVA-3V code was used for their study and

reported the possibility of reducing NOx and soot.

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Kamal Kishore et al., (2010) [120] have investigated experimentally on the

possibility of using karanj oil blended with petro-diesel in a diesel engine. An

additional set up was attached to the engine using which viscosity of the blend can be

reduced. Finding the optimum injection timing was their major concern. Engine

performance was taken into account while optimizing the injection time.

2.7 Summary

In the literature survey, contributions of eminent researchers in the field of CI

engines have been reviewed. The review of literature revealed the progress made in

the field of modelling of in-cylinder flows of diesel engines. It is clear that the

research in this direction has started early in 1980’s. The progress in the 3D modelling

is witnessed form the 1990’s. Accurate prediction of engine processes such as in-

cylinder flows, spray, combustion and pollutant formation is also witnessed in the

recent period. From the literature survey it is observed that the initial air swirl,

number of nozzle holes and the fuel injection time are controlling the quality of

combustion.

From the literature it is found that the engine performance depends on many

interdependent parameters. They are engine efficiency, fuel economy, injection

pressure, operating pressure, operating temperature, engine design, engine geometry,

combustion process, compression ratio, nozzle geometry, injection orientation,

injector location, injector geometry, injection strategies, geometry of the ports, bowl

geometry, distribution of air fuel mixture within the chamber. In order to improve the

engine performance, it is necessary to optimize all the above interdependent

parameters.

From the literature it is found that researchers have attempted with many

combinations of the above stated parameters but not many with the combination of

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swirl, number of injector holes and the injection time. Influences of these variables on

the performance of an engine are reported below:

• Swirl in diesel engines is an important parameter that affects the mixing of the

air fuel ratio and the quality of combustion, in turn heat release, emissions and

overall engine performance.

• There is an optimal level of swirl ratio for a particular combustion chamber.

Swirl level can be varied with appropriate design changes of the intake

system.

• Number of nozzle holes of a fuel injector in diesel engines is another

important parameter that affects the mixing of the air and fuel, in turn the

quality of combustion.

• There is an optimal number of nozzle holes for a particular combustion

chamber geometry.

• Fuel injection time in diesel engines is yet another important parameter that

affects the mixing of the air and fuel in turn the quality of combustion.

• There is an optimal injection time for particular combustion chamber

geometry.

Hence the present work aims at studying the influence of Swirl, Number of

nozzle holes of fuel injector and injection time in improving the quality of

combustion.

2.8 Scope and Objectives of the Present Work

From the literature survey the prominence of Swirl, Number of nozzle holes of

fuel injector and injection time in improving the combustion is observed. Scope for

optimising the three parameters viz., swirl, number of nozzle holes and injection time

is also observed. It is also observed that though attempts are made in optimising the

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performance of IC engine with several combinations of various parameters no major

attempts are made with the combination of the said three parameters. In the present

work, an attempt is made with an objective of optimizing the swirl, number of nozzle

holes of fuel injector and the injection time. A numerical study was carried out on a

DI diesel engine to study the effect of these parameters on spray and combustion.

Recardo-Vectis, a 3 dimensional computational fluid dynamics code has been

used for this purpose. Chapter 3 covers the methodology and details of the models

that are used in the present work. This objective was fulfilled by following these

steps, (1) Identifying the optimum swirl ratio for the engine. (2) Identifying the

optimum number of nozzle holes against swirl ratio. (3) Identifying the optimum start

of injection for the optimum one that was identified from step (2).