e ect of water-in-heavy fuel oil emulsion on the non...

Scientia Iranica B (2016) 23(6), 2626{2640

Sharif University of TechnologyScientia Iranica

Transactions B: Mechanical Engineeringwww.scientiairanica.com

E�ect of water-in-heavy fuel oil emulsion on thenon-reacting spray characteristics under di�erentambient conditions and injection pressures: A CFDstudy

H. Nowruzi and P. Ghadimi�

Department of Marine Technology, Amirkabir University of Technology, Tehran, P.O. Box 15875-4413, Iran.

Received 20 December 2014; received in revised form 20 October 2015; accepted 11 January 2016

KEYWORDSNon-reacting spraycharacteristic;Water in heavy fueloil emulsion;Breakup;High injectionpressure;Back pressure.

Abstract. Emulsi�ed fuel is one of the main strategies to substitute the conventionalfossil fuel for the purpose of emission control and enhancement of fuel e�ciency. Accord-ingly, non-reacting spray characteristics of water-in-Heavy Fuel Oil (HFO) emulsion arenumerically investigated in the present study via CFD analysis. Three di�erent volumetricpercentages of water in HFO are investigated and compared with pure HFO. E�ects of fourdi�erent injection pressures on injected fuel spray characteristics are studied. Moreover,in uences of three di�erent ambient back pressures and two ambient temperatures areconsidered. For these purposes, the characteristics of spray penetration, cone angle, volume,and SMD are evaluated through the analyses of non-dimensional numbers. For modelingthe interaction of the fuel discrete phase and the gaseous continuous phase, Eulerian-Lagrangian multiphase formulation in OpenFOAM CFD toolbox is implemented. Fueldroplet tracking in Lagrangian scheme is applied by Lagrangian Particle Tracking method.Also, KH-RT as a hybrid breakup model for liquid fuel core breakup and standard modelof k � " in RANS for turbulence modeling are utilized. Numerical results are validatedagainst existing experimental data with suitable accordance. Longer spray penetrationlength, larger cone angle, and greater spray volume are achieved for the emulsi�edfuels.© 2016 Sharif University of Technology. All rights reserved.

1. Introduction

Heavy-duty diesel engines, due to their capability inhigh power generation, are very useful in various scopessuch as maritime industries. High emission of theseengines is considered as a limiting factor for theirdevelopment. Therefore, by establishing restrictiveregulations for emission control by the international

*. Corresponding author. Tel.: +98 21 64543117;Fax: +98 21 66412495E-mail addresses: [email protected] (H. Nowruzi);[email protected] (P. Ghadimi)

community, a global movement is shaped to do researchon di�erent strategies for reducing the emission.

Among the proposed strategies, in-cylinder tech-niques have been more appealing from the perspectiveof emission control and improvement of fuel e�ciency.Increasing the injection pressure, lowering the intaketemperatures, and Exhaust-Gas Recirculation (EGR)are some of these strategies [1].

There are di�erent emissions from diesel engineexhaust. However, controlling the NOx pollution is oneof the most important issues that has attracted theresearchers' attention. The most signi�cant physicalphenomenon that has exponential in uence on the NOx

H. Nowruzi and P. Ghadimi/Scientia Iranica, Transactions B: Mechanical Engineering 23 (2016) 2626{2640 2627

formation rate is higher temperature [2,3]. Conse-quently, Low Temperature Combustion (LTC) methodwith the aim of reducing the temperature in thecombustion chamber has recently become interestingfor some scholars [4,5]. While the addition of waterto the combustion chamber is one of the in-cylinderstrategies, it can also be stated that water in fuelemulsion is considered as a popular technique in the�eld of water adding methods [6].

Use of emulsi�ed fuels in diesel engines, becauseof decreasing the peak of combustion ame tempera-ture, leads to NOx control. Furthermore, better air-fuel mixture is achieved by longer ignition delay inthe emulsi�ed fuel. Ignition delay up to 30-60% inthe emulsi�ed fuel rather than pure diesel fuel wasreported by laser-based study of Musculus et al. [7].Moreover, improvement of atomization procedure andhomogeneity in air-fuel mixture is anticipated bymicro-explosion of water droplets in the emulsion [8].Reacting characteristics of the emulsi�ed fuel spraywith volume percentages of 10% and 20% of waterwere experimentally investigated by Huo et al. [9].Increase of spray penetration length in the emulsi�edfuel was one of their �ndings. Ballester et al. [10]performed an experimental study on a semi-industrialscale on the combustion characteristics of heavy oil-water emulsion. In another study, the impact ofapplying water-in-diesel emulsion on NOx and sootemissions was analyzed by Park et al. [11]. However,based on the cited literature, lack of indepth studyon the non-reacting characteristics of emulsi�ed fuelspray is quite evident. Therefore, the necessity of aphenomenological study on the spray characteristics ofemulsi�ed fuel under non-reacting condition is the mainmotivation for conducting the current study.

On the other hand, large diesel engines are com-monly fueled by Heavy Fuel Oil (HFO). These heavyfuels, due to their low quality, produce high level of pol-lutions. Therefore, the usage of blended fuels createdfrom HFO and alcohols, such as butanol, methanol,and ethanol, on spray characteristics and emissionshas been investigated in several studies [12,13]. Ac-cordingly, in the current study, Heavy Fuel Oil (HFO)is selected as a basic fuel in emulsion with water.Di�erent volumetric percentages of water in HFO leadto di�erent physical fuel properties that a�ect theinjected spray behaviors. Hence, in the present study,the in uences of three di�erent volumetric percentagesof water in emulsi�ed fuel are considered.

From another view point, in uence of the injec-tion pressure and ambient condition of the combustionchamber, including ambient temperature and backpressure, is considered in the injected spray behaviorand its non-reacting characteristics. Moreover, theincrease of turbulence in combustion chamber by in-creasing the injection pressure leads to formation of a

homogenous air-fuel mixture. This phenomenon wasconcluded by Nishida et al. [14] in an experimentalstudy on the in uence of high and ultra-high injec-tion pressures on the spray penetration and SMD ofdiesel fuel. In another analytical and experimentalstudy, non-reacting microscopic and macroscopic spraycharacteristics of biodiesels and diesel under ultra-highinjection pressures of 100, 200, and 300 MPa werestudied by Wang et al. [15].

Liquid fuel spray interaction with aerodynamicforce of continuous air phase in the combustion cham-ber is dependent on the ambient back pressure andtemperature as well as spray ow condition. Hence,liquid fuel spray exhibits di�erent behavior undervarious ambient and ow conditions [16,17]. In uenceof high back pressure on spray characteristics of plainjet injector in the comprehensive range of 100 kPato 1600 kPa was experimentally investigated by Yanget al. [18]. In their study, a monotonous reductionin SMD value was detected with an increase in backpressure. Roisman et al. [19] experimentally andtheoretically studied the in uence of ambient pressureon the penetration of a diesel spray. E�ects of di�erentfuel and ambient gas temperatures on diesel spraycharacteristics and in uence of wide range of backpressures under liquid swirl injection were studied byPark et al. [20] and Chen et al. [21], respectively.

Characteristics of emulsi�ed fuel spray underdi�erent ambient conditions are not well understood,especially under non-reacting and non-evaporating con-ditions. Therefore, one of the main novelties of thecurrent study is the investigation of non-reacting spraycharacteristics of emulsi�ed fuels under di�erent condi-tions, including di�erent injection pressures, chamberback pressures, and temperatures.

Nowadays, numerical software based on Compu-tational Fluid Dynamics (CFD) is an e�cient alter-native tool to evaluate the fuel spray characteristics.Di�erent commercial software such as KIVA [22], AN-SYS FLUENT [23], and AVL FIRE [24] can be used toaccomplish the intended task. However, developmentof an open source CFD toolbox, such as OpenFOAM,has recently received more attention [25,26].

Signi�cance of investigating the in uence of emul-si�ed fuel, ambient condition, and injection pressure onspray characteristics has been surveyed by the cited lit-erature. Accordingly, in this paper, non-reacting char-acteristics of emulsi�ed fuel under di�erent ambienttemperatures, back pressures, and injection pressuresare numerically evaluated.

2. Emulsion of water in HFO

As pointed out earlier, adding water to the combustionchamber is a strategy for emission control through LTCtechnique. In general, there are di�erent methods for

2628 H. Nowruzi and P. Ghadimi/Scientia Iranica, Transactions B: Mechanical Engineering 23 (2016) 2626{2640

adding water to the combustion chamber. However,emulsi�ed fuel has become a preferable method basedon �ve criteria: relative NOx reduction, e�ect on thePM emission, variability of water addition, lubricatingoil dilution, and expenditure [27].

In the structure of water-HFO emulsion, dropletsof one phase (water in the present study) are sur-rounded by sheets of the other uid (HFO). In addition,very little amount of surfactant with physical charac-teristics similar to pure HFO is used for the formationof the emulsi�ed fuel. Maximization of super�cialcontact area between two uids by activation of thesetwo uid surfaces is the mechanism of surfactantfor achievement of stable water and heavy fuel oilemulsion [28].

On the other hand, based on spatial distributionof water in basic fossil fuel, water-in-fuel and fuel-inwater are two discrete fuel emulsions. Water-in-fuelemulsion is a better selection for the emulsi�ed fuelin diesel engines [29] due to microexplosion of waterdroplets and small change in viscosity and physicalcharacteristics of the emulsi�ed fuels. Therefore, water-in-HFO is the selected concept for the emulsi�ed fuel inthe current study. To model water-in-HFO, the NASAJannaf coe�cients as thermo-physical properties of thisemulsi�ed fuel are calculated and implemented in theOpenFOAM open source CFD toolbox. Physical char-acteristics of two components of the tested emulsi�edfuel are displayed in Table 1.

3. Technical description of the problem andgoverning equation

3.1. Physics of the liquid sprayIn the internal combustion engine, initially desired fuelas a liquid phase spray is injected into the gaseousenvironment of the combustion chamber. This liquidspray has three distinct structural zones: Atomiza-tion, dense spray, and dilute spray regions. In theatomization region, blobs as a massive continuousliquid agglomeration, ligaments, and small amount ofdroplets exist. Moreover, primary breakup in the formof disintegration of the liquid fuel core into ligamentsas non-spherical liquid sheets and droplets occurs inthis region. On the other hand, the secondary breakupleads to decomposition of blobs into ligaments andsimilarly, ligaments to the spherical droplets in thedense spray and dilute spray regions [30].

Table 1. Component of emulsi�ed fuel properties.

Physical characteristics Heavyfuel oil

Water

Viscosity at 20�C (m2s�1) 1.2e-5 1.004e-6Density at 20�C (kg/m�3) 895 895Surface tension (Nm�1) 0.029 0.0728

3.2. Computational procedureEulerian-Lagrangian multiphase scheme is adopted inthe current study for modeling fuel-air interaction inthe combustion chamber. Behavior of continuous airphase is predicted by �ve partial di�erential equationsin the Eulerian approach. Based on the study con-ducted by Nowruzi et al. [13], continuity equation,vector component of momentum conservation, andconservation of energy equations are solved in Eule-rian approach. For turbulence modeling in Eulerianapproach, standard turbulence model of k�" is used inthe unsteady RANS equation. Conservation equationsare discretized by FVM, and PIMPLE algorithm (com-bination of SIMPLE and PISO) is implemented for thevelocity-pressure coupling in OpenFOAM software. Inthe current study, selected time step for time marchingprocedure is assumed to be 1:0� 10�6 s.

Lagrangian Particle Tracking (LPT) scheme isapplied for evaluation of non-spherical particles orien-tation and rate of rotation [30]. For this purpose, sprayequation is used as the probability in the conditionspace of the randomized variables as in:@f@t

+rx(fu) +rv�f@u@t

�+

@@r

�f@r@t

�+

@@T

�f@T@t

�+

@@y

�f@y@t

�+

@@ _y

�f@ _y@t

�= _fco + _fbr: (1)

The term F = dV=dt illustrates the acceleration ofa single droplet in Eq. (1) [30]. Also, the termf(X;V; r; Td; T; y; _y; t)dV drdTddyd _y shows a probablenumber of droplets per unit volume. The sourceterms in Eq. (1) are contributions due to the e�ectsof collision of the droplets and droplets breakup.

3.3. Spray breakup modelingGenerally, due to complexity of simulating the primarybreakup in high density and pressure liquid core nearthe injector nozzle, initial droplets radius and sprayangle are considered as initial conditions. Based on thisassumption, blob method that presented by Reitz andDiwakar [31,32], which is a popular primary breakupmodel, is implemented for the primary breakup mod-eling in the current study.

On the other hand, there are di�erent methodsfor modeling the secondary breakup as impressiveprocedure for simulating the high injection pressure.Two major dimensionless numbers including Weberand Reynolds numbers are de�ned in modeling thesecondary breakup. The Weber number of the gaseousphase is de�ned as:

Weg =�gu2

relDd

�; (2)

where Dd is the diameter of the fuel droplet. Reynolds


number is another dimensionless number for showingthe e�ect of viscosity on the breakup procedure. TheReynolds number of gaseous phase is given by:

Re =urelDd

�g; (3)

where �g is the gas kinematic viscosity.Nowadays, hybrid breakup model is implemented

for modeling the comprehensive secondary breakup.One of these hybrid methods is KH-RT which combinesthe KH and RT instabilities.

Kelvin-Helmholtz (KH) model or a Wave model ispresented by Reitz [33]. The idea behind this methodis the Kelvin-Helmholtz instability growth analysis onthe cylindrical liquid jet surface with primary radius ofr0. The wavelength (KH) and growth rate (�KH) ofthe fastest growing wave on the surface of the liquid jetare de�ned as:

KH

��lr3

0�

�0:5

=0:34 + 0:38:We1:5

g

(1 + Oh)(1 + 1:4:T 0:6); (4)

�KH

r0= 9:02

(1 + 0:45:Oh0:5)(1 + 0:4:T 0:7)(1 + 0:865:We1:67

g )0:6; (5)

where the dimensionless numbers Oh, T , Weg, and Welcan be measured as in:

Oh =p

WelRel

; T = Ohp

Weg;

Weg =�gu2

relr0

�; Wel =

�lu2relr0

�: (6)

Here, Oh and T are dimensionless Ohnesorge numberand Taylor number, respectively. Moreover, the rate ofchange of the droplet radius in KH model is given by:

drdt

= �r0 � rc�bu

; (7)

where rc is the radius of new droplet (child droplet) and�bu is the dimensionless time of breakup (characteristicsof breakup time), and they are de�ned as follows:

rc = B0:�KH; (8)

�bu = 3:788:B1r0

�KH:KH; (9)

where KH breakup model is valid when:

B0:�KH � r0: (10)

In the RT model, the growth rate of the fastest growingwave (RT) and the corresponding wavelength (�RT),based on the study of Bellman and Pennington [34], is:

RT =

s2

2p

3�[a(�l � �g)]3=2

�l + �g; (11)

�RT = C32�

s3�

a(�l + �g): (12)

Consequently, based on the study of Ghasemi et al. [35]that introduces the KH-RT model as a more accurateprediction for the secondary breakup, the KH-RTbreakup model is utilized in the current study.

3.4. Grid generation and validationTo validate the non-reacting spray characteristics ofwater-in-HFO emulsion fuel, a grid resolution sensitiv-ity analysis is initially conducted for HFO at injectionpressures of 60 and 100 MPa. Subsequently, based onan adopted mesh structure, two major properties ofspray penetration length and spray cone angle of HFOare computed and validated against the experimentaldata [36].

For grid resolution sensitivity analysis, four dif-ferent fully structured meshes (ranging from coarsemesh resolution of 0.004 m to �ner mesh resolution of0.001 m) are studied for injection pressures of 60 and100 MPa in Figures 1 and 2, respectively. Afterward,

Figure 1. Grid independency test of HFO spraypenetration length at injection pressure of 60 MPa.

Figure 2. Grid independency test of HFO spraypenetration length at injection pressure of 100 MPa.


Figure 3. Comparison of numerical and experimental spray penetration length and spray cone angle of HFO at injectionpressure of 60 MPa [36].

Figure 4. Comparison of numerical and experimental spray penetration length and spray cone angle of HFO at injectionpressure of 100 MPa [36].

by a selected proper mesh structure (0.00133 m),computational results of spray penetration length andspray cone angle of HFO at injection pressures of60 and 100 MPa are validated against experimentaldata [36] in Figures 3 and 4, respectively.

According to Figure 3, the RSME of penetrationlength and spray cone angle at injection pressure of60 MPa are 5.46 and 2.51, respectively. Moreover,based on Figure 4, the RSME of penetration lengthand spray cone angle at injection pressure of 100 MPaare 3.21 and 2.34, respectively.

Moreover, to demonstrate the accuracy of theselected numerical setup for modeling the emulsi�edfuels, a comparative study is conducted in Figure 5.

Figure 5. Comparison of numerical and experimentalspray penetration length of diesel-water emulsion (by 18%volume percentage of water) at injection pressure of 60and 100 MPa [36].

As observed, suitable accordance is obtained betweenthe current result and experimental data with RSMEof 2.14 for 60 MPa and 2.31 for 100 MPa.

3.5. Numerical model speci�cation and sprayanalysis criteria

In the current study, water-in-HFO is injected to con-stant volume combustion chamber through a single holeinjector. Injection mass ow rate for di�erent ambientconditions and injection pressures is calculated basedon the study of Pickett et al. [37]. The combustionchamber and injection setup of the present study arepresented in Table 2.

To evaluate the behavior of the non-reactingliquid spray, we evaluated spray penetration length,spray cone, and SMD. Pictorial description of the liquid

Table 2. Combustion chamber and injection setup.

Model parameter Value

Combustionchamber

parameters

Length (mm) 450Diameter (mm) 150Back pressure (MPa) 1.4Ambient temperature (K) 298

Injectionparameters

Nozzle diameter (mm) 0.27Fuel injection pressure (MPa) 60Injection total mass (mg) 34


Figure 6. De�nition of spray penetration length and halfspray cone angle.

spray penetration length and half spray cone angle areprovided in Figure 6.

Moreover, SMD as a targeted microscopic char-acteristic is calculated by the average diameter of allgroups of droplets at a particular time.

4. Results and discussion

Numerical results and discussion of microscopic andmacroscopic non-reacting spray characteristics of dif-ferent water-in-HFO under di�erent ambient conditionsand injection pressures are presented in this section.

4.1. Analysis on the non-dimensional numberThree dimensionless numbers are considered for thepresent study: Weber (We) number, Reynolds number(Re), and Ohnesorge number (Oh). Relation betweenWe and Oh numbers for all liquid droplets of HFOE0(Pure HFO without water content) and HFOE20 (20%water as an emulsion in HFO) at 1.5 ms after thestart of injection is illustrated in Figures 7 and 8,respectively. Based on Figures 7 and 8, the minimumof Weber number is approximately the same for bothutilized fuels. However, the maximum value of We-ber number is larger for HFOE0 that indicates thehigher e�ect of the surface tension in HFOE20. Also,Hardalupas et al. [38] proved that the magnitude of theWeber number indicates that droplet breakup is alwayslimited to the leading edge of the fuel spray.

On the other hand, slight relocation in clouddroplet of Oh number toward larger value is evident forHFOE0. Therefore, it can be concluded that HFOE0

Figure 7. Weber number VS Ohnesorge number forHFOE0 at 1.5 ms after the start of ignition(Pinj = 60 MPa, Pback = 1:4 MPa, Tamb = 298 K).



is more a�ected by the viscosity due to its larger Ohnumber.

Moreover, for studying the e�ect of injectionpressure on the structure of We-Oh droplet cloud, therelation between We and Oh numbers for all liquiddroplets of HFOE0 at injection pressure of 300 MPa,compared to that of HFOE20 at injection pressureof 60 MPa in Figure 8, is presented in Figure 9.Slight enhancement in Weber number and insigni�cantchange in the Ohnesorge number are detectable byan increase in the injection pressure from 60 MPa to300 MPa.

In uence of the injection pressure on the Renumber for HFOE20 can be observed in Figure 10.

Based on Figure 10, Reynolds number exhibitsa parabolic increase, when the injection pressure in-creases.

4.2. E�ect of volumetric percentage of waterin emulsi�ed fuel

To study the in uence of di�erent volumetric percent-ages of water in the emulsi�ed fuel, three di�erentemulsi�ed fuels with di�erent volumetric percentagesof water (as shown in Table 3) are compared with pureHFO.


Figure 10. Average Reynolds number of HFOE20 fordi�erent injection pressure at 1.5 ms ASOI(Pback = 1:4 MPa, Tamb = 298 K).

Figure 11. Liquid spray structure for di�erent volumetricpercentage of water in emulsi�ed fuel at 1.5 ms after thestart of ignition (Pinj = 60 MPa, Pback = 1:4 MPa,Tamb = 298 K).

Table 3. Di�erent volumetric percentages of water inemulsi�ed fuel.

Casestudy

Volumetricpercentage

of water

Otherenvironmentalcharacteristics

HFOE0 0%Injection pressure = 60 MPaBack pressure = 1.4 MPaAmbient temperature = 298 K

Before studying the e�ects of di�erent emulsi�edfuels, spray structure morphology for di�erent volumet-ric percentages of water in the emulsi�ed fuel at 1.5 msafter the start of injection is provided in Figure 11.

Based on Figure 11, bulkier spray with sharper tipis apparent in the emulsi�ed fuel as opposed to the pureHFO (HFOE0). Also, these phenomenological changesare more signi�cant in the emulsi�ed fuel with morewater content.

Subsequently, the e�ects of di�erent volumetricpercentages of water in the emulsi�ed fuel on thespray characteristics are studied. For this purpose,spray penetration length, spray cone angle, sprayvolume, and Sauter Mean Diameter (SMD) for di�erentvolumetric percentages of water in the emulsi�ed fuelare presented in Figure 12.

Based on Figure 12(a), it is found that all emulsi-�ed fuels with di�erent volumetric percentages of waterhave longer spray penetration. Linear growing rateuntil 0.5 ms ASOI with asymptomatically trend afterthis time is detectable for both pure HFO (HFOE0)and all emulsi�ed fuels. Also, HFOE20 with higherwater content has insigni�cant longer spray penetrationlength than other emulsi�ed fuels. This phenomenoncan be the result of an increase in density and adecrease of dynamic viscosity in the emulsi�ed fuel.However, due to the increase of surface tension ofthe emulsi�ed fuel, the penetration length is not sig-ni�cant [15,39]. In addition, based on Figure 12(b),spray cone angle of the emulsi�ed fuels is decreasedin a temporal trend after the start of injection. Also,spray cone angle of the emulsi�ed fuels has signi�cantlygreater value than that of HFOE0. Moreover, largervolume percentage of water content in the emulsionleads to an increase of spray cone angle, especially after1.5 ms. Also, HFOE5, as an emulsi�ed fuel, o�ers aconsiderable longer spray cone angle than HFOA0. Inthe meantime, all emulsi�ed fuels (HFOE5, HFOE15,and HFOE20) have approximately similar spray coneangles.

Based on spray volume in Figure 12(c), betterrecognition of air-fuel mixture study is prepared. More-over, the addition of water content in the emulsi�ed fuelcauses greater spray volume, especially after 1.0 ms.Consequently, a better homogeneity in air-fuel mixtureis expected from the emulsi�ed fuels due to larger pen-etration length, spray cone angle, and spray volume.

Based on Figure 12(d), emulsi�ed fuels have largerSMD quantity, and an increase in volumetric percent-age of water in the emulsion leads to larger SMD. Thisobservation can be attributed to a signi�cant decreasein the dynamic viscosity of the emulsi�ed fuels ratherthan pure HFO.

4.3. E�ect of injection pressure on Emulsi�edfuel

To study the e�ect of di�erent injection pressureson liquid spray properties, four di�erent injectionpressures ranging from medium pressure of 60 MPato ultra-high pressure of 300 MPa are considered.The in uence of injection pressures is implemented forHFOE20 as the selected emulsi�ed fuel and pure HFO(HFOE20) as presented in Table 4.

To study the e�ect of di�erent injection pressureson the emulsi�ed fuel spray morphology, liquid spraystructure for di�erent injection pressures of HFOE20is illustrated in Figure 13 at 1.5 ms ASOI. Based onFigure 13, general perspective of the spray structure isapproximately similar to HHFOE20 at di�erent injec-tion pressures. However, the fattest spray structure isdetectable for HFOE20 at ultra-high injection pressureof 300 MPa.


Figure 12. (a) Spray penetration length, (b) spray cone angle, (c) spray volume, and (d) SMD for di�erent volumetricpercentages of water in the emulsi�ed fuel (Pinj = 60 MPa, Pback = 1:4 MPa, Tamb = 298 K).

Table 4. Cases of di�erent injection pressures for HFOE0 and HFOE20.

Case studyInjection pressure

(MPa)Other environmental

characteristicsHFOE0 @ 60 MPa 60

Back pressure = 1.4 MPaAmbient temperature = 298 K

HFOE20 @ 60 MPa 60HFOE0 @ 100 MPa 100HFOE20 @ 100 MPa 100HFOE0 @ 200 MPa 200HFOE20 @ 200 MPa 200HFOE0 @ 300 MPa 300HFOE20 @ 300 MPa 300

Figure 13. Liquid spray structure for di�erent injectionpressures of HFOE20 at 1.5 ms ASOI (Pback = 1:4 MPa,Tamb = 298 K).

Macroscopic characteristics of spray penetrationlength, spray cone angle, spray volume, and micro-scopic criterion of Sauter Mean Diameter (SMD) forHFOE0 and HFOE20 at di�erent injection pressuresare displayed in Figure 14. Based on Figure 14(a), with

homologous behavior, an increase in penetration lengthis detected with an increase in injection pressure forboth HFOE0 and HFOE20. This happens because ofthe spray pressure augmentation related to ambient airresistance [14,15]. Also, insigni�cant e�ects of injectionpressure increase on the spray penetration length ofHFOE0 are evident until 0.5 ms ASOI. Furthermore,the use of HFOE20 instead of HFOE0 is proved to leadto a higher penetration length compared to the e�ectof increasing the injection pressure from 60 MPa to300 MPa for HFOE0.

According to Figure 14(b), larger spray coneangle is observable in HFOE20 than HFOE0 at allinjection pressures. However, increase in injectionpressure has negligible e�ect on the spray cone angleof the emulsi�ed fuels. However, greater spray coneangle is obtained in HFOE0 by increasing the injectionpressure, especially for a pressure increase of 60 to100 MPa. Based on Figure 14(c), an increase ininjection pressure leads to larger spray volume for both


Figure 14. (a) Spray penetration length, (b) spray cone angle, (c) spray volume and (d) SMD for di�erent injectionpressure of HFOE20 and pure HFO (Pback = 1:4 MPa, Tamb = 298 K).

HFOE0 and HFOE20, especially for HFOE20 and fora pressure increase of 10 MPa to 200 MPa.

According to Figure 14(d), lower SMD value isachieved by higher injection pressure for both fuels.Hence, the e�ect of higher SMD of the emulsi�ed fuelscan be reduced by higher injection pressure. Dueto growth of instabilities on the liquid spray surface,better atomization procedure is anticipated for higherinjection pressure for both fuels. The obtained resultsof SMD are in accordance with those of study of Wanget al. [15].

4.4. E�ect of di�erent back pressure onemulsi�ed fuel

Based on Table 5, the e�ects of three back pressuresare studied on spray characteristics and morphology ofHFOE20 as emulsi�ed fuel and HFOE0.

Liquid spray structure for di�erent back pressuresof HFOE20 at 1.5 ms ASOI and injection pressureof 60MP is presented in Figure 15. As evident inFigure 15, due to the shock wave in ambient air againstthe injected spray, sharper spray tip is detectable for1.4 MPa. Moreover, more compact spray structure

Figure 15. Liquid spray structure for di�erent backpressures of HFOE20 at 1.5 ms ASOI (Pinj = 60 MPa,Tamb = 298 K).

with conical tip is achieved for HFOE20 at backpressure of 2.8 MPa. These phenomena can be theresult of an increase in the aerodynamic resistance ofambient gaseous air in the face of liquid spray structure.

Microscopic and macroscopic characteristics of


Table 5. Cases of di�erent back pressures for HFOE0 and HFOE20.

Case study Back pressure(MPa)

Other environmentalcharacteristics

HFOE20 @ 1 MPa 1

Injection pressure = 60 MPaAmbient temperature = 298 K

HFOE20 @ 1.4 MPa 1.4HFOE0 @ 1.4 MPa 1.4HFOE20 @ 2.8 MPa 2.8HFOE0 @ 2.8 MPa 2.8

Figure 16. (a) Spray penetration length, (b) spray cone angle, (c) spray volume, and (d) SMD for di�erent back pressuresof HFOE20 and pure HFO (Pinj = 60 MPa, Tamb = 298 K).

HFOE0 and HFOE20 are illustrated in Figure 16 fordi�erent back pressures. Based on Figure 16(a), it canbe concluded that with an increase in chamber backpressure, spray penetration length is decreased due tothe reinforcement of the ambient uid resistance. Onthe other hand, reduction rate of penetration from backpressure of 1.4 MPa to 2.8 MPa for HFOE20 is morevisible compared to back pressure reduction for pureHFOE0.

Also, according to Figure 16(b), one can observethat di�erent back pressures have no signi�cant in u-ence on the spray cone angle for both HFOE0 andHFOE20, especially until 1 ms ASOI. In addition,similar to the penetration length, greater spray volume

for HFOE20 at atmospheric back pressure of 1 MPa isdetectable in Figure 16(c).

On the other hand, based on Figure 16(d), higherback pressure leads to greater value of SMD for bothHFOE0 and HFOE20 fuels. The reason for thisphenomenon can be found in the delay of atomizationprocedure with aerial aerodynamic force due to thehigher back pressure.

4.5. E�ect of di�erent ambient temperatureon emulsi�ed fuel

The spray penetration, spray cone angle, and sprayvolume for two di�erent chamber ambient tempera-tures under the conditions of Table 6 are presented


Table 6. Cases of di�erent temperature for HFOE20.

Case study Ambient temperature(K)

Other environmentalcharacteristics

Ambient air temperature = 298 K 298 Injection pressure = 60 MPaAmbient back pressure = 1.4 MPa

Figure 17. Spray penetration length, spray cone angle, and spray volume for di�erent ambient temperatures of HFOE20(Pback = 1:4 MPa, Pinj = 60 MPa, Tamb = 298 K).

in Figure 17. Based on Figure 17, one can observethat temporal spray penetration length increases forHFOE20 by an increase in chamber ambient tempera-ture from 298 K to 498 K. Also, an increase in the spraypenetration length leads to greater growth rate in time-line. However, lower spray cone angle is revealed byincreasing ambient temperature from 298 K to 498 K.

Moreover, greater spray volume is achieved by theambient temperature increase.

Furthermore, based on Figure 18, chamber ambi-ent temperature increasing from 298 K to 498 K leadsto a decrease in SMD for HFOE20. This reduction

Figure 18. SMD for di�erent ambient temperature ofHFOE20 (Pback = 1:4 MPa, Pinj = 60 MPa,Tamb = 298 K).

is considerable and leads to half value of the SMD athigher ambient temperature. Reduction of SMD is dueto an increase in injected fuel (HFOE20) temperatureby an increase in ambient temperature. As a result ofthe temperature rise in HFOE20, its surface tension,viscosity, and density are decreased [36].

On the other hand, lower viscosity increasesthe instabilities required for the injected fuel jet tobreakup. This accelerates the atomization procedureand leads to lower SMD value. In addition, reduction ofthe injected fuel density directly impacts the atomiza-tion procedure [40]. Moreover, higher surface tensionacts against the formation of smaller droplets fromthe liquid fuel [39]. Therefore, a decrease in surfacetension improves the atomization procedure and resultsin lower SMD.

Based on the stated reasons, a decrease in SMDfor HFOE20 can be expected due to an increase inchamber ambient temperature. Meanwhile, this de-crease in SMD value by ambient temperature increaseis consistent with the result of the study of Park etal. [20].


Table 7. A summary of the observations for di�erent applied fuels.

Spray parameterSubstitution of HFOE20 instead

of HFO (Pinj = 60 MPa,Pback = 1.4 MPa, Tamb = 298 K)

Adding water from 5% to 20%in emulsion (Pinj = 60 MPa,

Pback = 1.4 MPa, Tamb = 298 K)Spray penetration 23.75 % " 21.47 % "Spray cone angle 100.81 % " 4.9 % "Spray volume 57.92 % " 2.87 % "SMD 14.09 % " 9.43 % "" represents higher comparative value.

Table 8. A summary of the observations for di�erent ambient conditions.

Spray parameterInjection pressure

enhancementfrom 60 MPa to 300 MPaa

Back pressureenhancement

from 1 MPa to 2.8 MPab

Ambient temperatureenhancement

from 298 K to 498 Kc

Spray penetration 27.35% " 55.5% # 14.27% "Spray cone angle 6.53% " 3. 94% # 24.74% "Spray volume 92.0% " 250.06% # 2.87% "SMD 140.66% # 1.68% " 4. 03% #

a Pback = 1:4 MPa, Tamb = 298 K; b Pinj=60 MPa, Tamb=298 K; c Pback=1.4 MPa, Pinj=60 MPa." Represents higher comparative value; # Represents lower comparative value;

The average of the relative in uence of wateraddition to pure HFO fuel and the e�ect of addingwater from 5% to 20% in emulsion are summarizedin Table 7. Also, a summary of the observationsfor di�erent ambient conditions and di�erent injectionpressures of HFOE20 is presented in Table 8.

Based on the demonstrated results of Tables 7and 8, larger spray penetration, spray cone angle,and spray volume in emulsi�ed fuels o�er a betterair-fuel mixture. Furthermore, smaller value of SMDrepresents a better atomization procedure at lower backpressure and higher temperature.

5. Conclusions

Non-reacting spray characteristics of the emulsi�edfuels (alternative fuel with tha aim of increasing thefuel e�ciency) are assessed in the present study.

For this purpose, three di�erent volume percent-ages (5%, 15%, and 20%) of water in emulsion are usedin comparison with pure HFO. Moreover, behavior ofthe selected emulsi�ed fuel and pure HFO are evaluatedunder di�erent injection pressure, back pressures, andambient temperatures. For evaluation of the spraycharacteristics, the microscopic and macroscopic spraycriteria are investigated after the analyses of the non-dimensional numbers including Weber, Ohnesorge, andReynolds.

To carry out the intended study, the open sourceCFD toolbox of OpenFOAM is utilized. Eulerian-Lagrangian multiphase scheme, Hybrid breakup modelof KH-RT, and Lagrangian Particle Tracking (LPT)

method are used for turbulence modeling in Eulerianscheme; standard model of k�" in RANS is performed.

First, a grid sensitivity analysis for the HFO isconducted. Then, spray penetration length and spraycone angle for HFO are validated with appropriateaccordance. Based on the obtained computational re-sults, spray penetration length of the emulsi�ed fuels islarger than that of pure HFO. Moreover, values of spraycone angle and spray volume increase by replacing thepure HFO by emulsi�ed fuels. However, due to increasein surface tension and signi�cant decrease in dynamicviscosity of the emulsi�ed fuels, larger SMD value ismeasured for the emulsi�ed fuels. It was also concludedthat by increasing the volumetric percentage of waterin the emulsi�ed fuel, the macroscopic spray criteriaare improved.

On the other hand, with an increase in injectionpressure from 60 MPa to ultra-high value of 300 MPa,the spray penetration length is increased for bothemulsi�ed fuel (HFOE20) and pure HFO. Also, due tothe increase in surface tension of the emulsi�ed fuels, anincrease in injection pressure has negligible in uence onthe spray cone angle of the emulsi�ed fuels, but leads togrowing spray volume for both HFOE0 and HFOE20,especially for HFOE20, when the injection pressureincreases from 100 MPa to 200 MPa. Meanwhile, lowerSMD value is achieved by higher injection pressure forboth fuels.

Based on the studies performed on the e�ect ofdi�erent back pressures, one can easily see that with anincrease in chamber back pressure, spray penetrationlength is decreased. Also, reduction rate of penetration


from back pressure of 1.4 MPa to 2.8 MPa for HFOE20is more visible compared to back pressure reduction forpure HFOE0. On the other hand, higher back pressureslead to greater value of SMD for both HFOE0 andHFOE20 fuels. This can be attributed to the lag ofbreakup procedure with aerial aerodynamic force dueto higher back pressure.

From another point of view, an increase in tem-poral spray penetration length is observed for HFOE20by increasing the chamber ambient temperature from298 K to 498 K. However, a lower spray cone angle isdisplayed by increasing the ambient temperature from298 K to 498 K. Furthermore, due to the decrease insurface tension, viscosity, and density of HFOE20, anincrease in chamber ambient temperature leads to thereduction of SMD for HFOE20.

Overall, it is concluded that the emulsi�ed fuelrepresents a better air-fuel mixture because of largerspray penetration, spray cone angle, and spray volume.Also, an improved atomization procedure with lowerSMD value of emulsi�ed fuel can be achieved by higherinjection pressure, ambient temperature, and lowerback pressure.

Nomenclature

Latin letters

HFO Heavy Fuel Oil;PM Particulate Matter;RANS Reynolds Averaged Navier Stokes;RMSE Root Mean Square Error;ASOI After Start Of Injection;SMD Sauter Mean Diameter;SIMPLE Semi Implicit Method for Pressure

Linked Equations;LPT Lagrangian Particle Tracking;_fco Contribution due to the e�ects of

collision of the droplets;_fbr Contribution due to the e�ects of

droplets breakup;Wel Liquid fuel Weber number;Weg Gas Weber number;urel Relative speed between droplets and

ambient gas (m.s�1);Dd Diameter of fuel droplet (m);Rel Liquid fuel Reynolds number;r0 Droplet radius before breakup (m);rc Radius of child droplets (m);Oh Ohnesorge number;T Taylor number;

Pinj Injection pressure (MPa);Pback Ambient back pressure (MPa);Tamb Ambient temperature (K).

Greek letters

�KH Kelvin-Helmholtz wavelength (m);�RT Rayleigh-Taylor wavelength (m);KH Kelvin-Helmholtz growth rate (s�1);RT Rayleigh-Taylor growth rate (s�1);�g Gas density (kg.m�3);

�l Liquid fuel density (kg.m�3);�bu Characteristic time (s);� Surface tension (N.m�1);�g Gas kinematic viscosity (m.s�1);! Instability wave growth rate.

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Biographies

Hashem Nowruzi was born in Tehran, Iran in 1990.He received his BSc degree in Marine Engineering fromAmirkabir University of Technology (AUT), Tehran,Iran, in 2012. He then received his MS degree inShip Hydrodynamics in Dept. of Marine Technology,from Amirkabir University of Technology, in 2014.He is currently a PhD student in the same �eldand university. His research interests include CFD

modeling of hydrodynamics phenomena and high pres-sure diesel injection. He has co-authored 7 scienti�cpapers in the �eld of computational uid dynamics andhydrodynamics.

Parviz Ghadimi received his PhD in MechanicalEngineering in 1994 from Duke University, USA. Heserved one year as a Research Assistant Professor inM.E. and six years as a Visiting Assistant Professorin Mathematics Department in Duke. He joinedthe Department of Marine Technolgy in AmirkabirUniversity of Technology (Tehran, Iran) in Fall 2005as an Assistant Professor of Hydromechanics, and iscurrently a Professor and Associate Chair of GraduateStudies in the same department. His main research in-terests include hydrodynamics, hydroacoutics, thermo-hydrodynamics, and CFD. Dr. Ghadimi has authoredseveral scienti�c papers in these �elds and has also au-thored two textbooks in Farsi: Applied ComputationalFluid Dynamics and Engineering Mathematics.

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