Presented byDr. N. NALLUSAMY Professor / Mechanical Engg. SSN College of EngineeringOMR, Kalavakkam, Chennai

Experimental study on spray characteristics of diesel and biodiesel (Jatropha oil methyl ester) for various chamber

pressures in a constant volume chamber

Requirement of alternate fuels

Petroleum products consumption is increasing day-by-day as the number of vehicles-on-road increases.

Consumption of hydrocarbon fuel increases the environmental pollution also.

There is a need to solve these twin problems–fuel supply and environmental pollution.

Conventional fuels emit more hydrocarbon emissions, oxides of nitrogen, sulphur and carbon monoxides as compared to renewable biofuels.

Requirement of alternate fuels … Various alternative fuels are considered as

substitute fuels for petroleum products.

Efforts were made to analyze the suitability of the fuel and its demonstration in the last two decades.

Renewable fuels have received more attention as - it reduces the environmental pollution (by completing carbon cycle) and - reduces the import of petroleum based fuels.

Requirement of alternate fuels …

Hence, researchers and scientific community worldwide

have focused on • development of biodiesel

• optimization of the processes to meet the standards and specifications needed for the fuel to be used commercially.

Biodiesel from vegetable oils

• Among the different renewable fuels considered for the use, the biodiesel derived from vegetable oils (available from plant sources) are realistic alternatives to diesel fuel

because they are renewable in nature and environment-friendly.

BIO-DIESEL:“A fuel comprised of mono-alkyl esters of long chain fatty acids derived from vegetable oils or animal fats, designated B100, and meeting the requirements of ASTM D 6751”

Biodiesel feedstocks• Jatropha• Pongamia Pinnata• soybean • sunflower• Rapeseed• Coconut oil• Palm oil• Cotton seed oil• Castor oil• Waste cooking oil

Advantages of Biodiesel

It is renewable and energy efficient It displaces petroleum-derived diesel fuel It can be used as a 20% blend in most diesel equipment with no or only minor modifications

It is environment friendly and does not produce greenhouse effects, because the balance between the amount of CO2 emissions and the amount of CO2 absorbed by the plants producing vegetable oil is equal.

Advantages of Biodiesel…

It can reduce tailpipe emissions, including air toxics

Biodiesel has a higher oxygen content (usually 10 to 12

percent) than petroleum diesel. This should result in lower pollution emissions.

Biodiesel has a higher cetane number than petroleum diesel

because of its oxygen content. The higher the cetane number, the more efficient the

fuel the engine starts more easily, runs better and burns

cleaner

AVERAGE BIODIESEL EMISSIONS COMPARED TO CONVENTIONAL DIESEL, ACCORDING TO EPA

• Emission Type B100 B20

• Unburned Hydrocarbons :    - 67%             ‐ 20%

• Carbon Monoxide ‐ 48%          ‐ 12%

• Particulate Matter ‐ 47%          ‐ 12%

• Nox + 10% + 2%

Drawbacks of using biodiesel as fuel in IC engines

• It is commonly accepted by researchers that- the use of biodiesel will lead to loss in engine power mainly due to the lesser calorific value of biodiesel compared to diesel, (~ 4%)- but there exists power recovery for biodiesel engine as the result of an increase in biodiesel fuel consumption.

• An increase in biodiesel fuel consumption, due to low heating value and high density and viscosity of biodiesel, has been found,

• but this trend will be weakened in diesel & biodiesel blends as the proportion of biodiesel reduces in the blend.

Biodiesel production methods

The liquid fuel produced has almost identical chemical components to conventional diesel fuel.

4. Transesterification – also called alcoholysis – chemical reaction of vegetable oil or animal fat with an alcohol (methanol) in the presence of a catalyst to form biodiesel (chemically called methyl esters) and glycerol.

Catalyst: NaOH, KOH

Triglycerides +Alcohol Alkyl ester +Glycerol 

Catalyst

Spray Characteristics in Diesel Engines

In Diesel engines the combustion process basically depends on - fuel injected into the combustion chamber and its interaction with the air.

The characteristics of the diesel spray have affected certain aspects of engine performance, such as- the power, fuel consumption, and emissions.

Therefore, it is essential to investigate the effects of various injection parameters to optimize the injection process.

Spray Characteristics in Diesel Engines

Several meaningful factors that have an influence, but the most important one is the diesel spray, more specifically the penetration of the liquid length of the spray through the combustion chamber or piston bowl.

The analysis of the liquid length penetration is very useful to determine the geometric design of Diesel engine combustion chambers with direct injection.

Macroscopic Characteristics

The macroscopic description of a diesel spray generally

emphasize the interaction of the latter and the control volume

where it is injected and mixed, and because of this the diesel

spray can be defined with the following physical parameters :

1. Spray tip penetration (spray length)2. Spray angle3. Break up length

Main integral characteristics of the spray are: breakup length, tip penetration length and spray cone angle.

Spray characteristics

The injection front penetration (S) (Spray tip penetration length)

is defined as the total distance covered by the spray in a control

volume.i.e. Length from the nozzle tip to the tip of

the spray

Spray characteristics

Cone angle:• The cone angle is defined as the angle formed by

two straight lines that start from the exit orifice of the nozzle and tangent to the spray outline (sprays morphology) in a determined distance. (equivalent to 60 times exit diameter of the nozzles orifice)

• This angle usually is between 5 and 30 degrees.

• This determines greatly the fuels macroscopic distribution in the combustion chamber

Spray characteristics - Sauters mean diameter

• The macroscopic description is characterized by the content of droplets of diverse sizes and the changes in their special kinetics.

• For example, the atomization mechanism is responsible for distributing the droplets in the injection process and to a great extent the good distribution of the droplets in relation to their size depend on it.

• A determined medium diameter represents the equivalent diameter that characterizes the entire group of the droplets of the spray.

Objective of the experimental study

The spray characteristics of fuel mainly depend on fuel injection process, fuel density, fuel viscosity, ambient pressure and temperature.

The effect of fuel injection pressure and ambient pressure are very important parameter directly affecting spray structure.

This study investigates the effects of chamber (ambient) pressure on the spray characteristics such as spray angle and spray tip penetration in a constant volume chamber under non evaporating conditions by image processing techniques.

Objectives ...

Images of spray under non-evaporative conditions are captured by a high speed digital camera for various chamber pressure.

The macroscopic (spray) characteristics such as spray coneangle and spray penetration are measured experimentally from the images.

Spray characteristics will be compared with that of diesel in order to understand the behaviour of biodiesel.

SCHEMATIC OF EXPERIMENTAL SETUP

EXPERIMENTAL SETUP

Steel chamber with heater

Property Diesel Jatropha oil methyl ester (Biodiesel)

Raw Jatropha

Vegetable Oil

Density(kg/m3) 840 875 917

Viscosity(400C)CP 3.4 4.27 35.58

Flash point(0C) 71 77 229

Fire point(0C) 103 270 300

Cetane number 48-56 51-52 23-41

Calorific value (MJ/kg) 45.343 38.5 39.071

Properties of diesel, Jatropha vegetable oil and Jatropha methyl ester (biodiesel)

Experimental data

Injection parameters:Injection pressure - 230 barChamber pressure - 1,2,3,4& 5 barChamber temperature - 300 KFuel & air temperature - 300 KNozzle diameter - 0.231 mmInjection duration - 1.2 ms

The spray images were captured using high speed digital

Camera (Nikon D200)

SPRAY IMAGES- DIESEL

Chamber pressure 1 bar Chamber pressure 2 bar

Chamber pressure 3 bar Chamber pressure 4 bar

Chamber pressure 5 bar

SPRAY IMAGES OF BIO DIESEL

Chamber pressure 1 bar Chamber pressure 2 bar

Chamber pressure 3 bar Chamber pressure 4 bar

Chamber pressure 5 bar

Parameters to studied

Spray tip penetration (spray length) Spray cone angle Sauter mean diameter (SMD) Spray volume

Images of diesel spray by varying the chamber pressure (1, 2, 3, 4 and 5 bar), injection pressure 230 bar and ambient temperature 300K

For these images• an initial spray angle was measured as the angle enclosing the initial part of the visible spray from the injector tip

• and spray penetration was measured from the nozzle tip to the tip of the spray.

EXPERIMENTAL RESULTS

DIESEL

Images of biodiesel spray by varying the chamber pressure (1, 2, 3, 4 and 5 bar), injection pressure 230 bar and ambient temperature 300K

EXPERIMENTAL RESULTS

BIODIESEL

Variation of spray tip penetration for diesel and JOME at various chamber

pressures.

RESULTS & DISCUSSIONSPRAY PENETRATION

LENGTH• Spray length decreases with increase in chamber pressure for both diesel and bio diesel.

• As the chamber pressure increases the density of (ambient gas)nitrogen also increases due to which shear resistance increases near the spray tip. This results in reduction of droplet velocity Hence the spray length decreases.

• The spray tip penetration for diesel is found to be the lower for all chamber pressures, this is because the density and viscosity of diesel is lower, hence it atomizes more rapidly compared to biodiesel fuels.

Experimental and theoretical values of Spray tip penetration for JOME

For jet atomization regime, spray penetration was found to follow the relationship proposed by Dent et al [9].

2

14

1

95.2 ng

tdP

S

(1)

Experimental and theoretical values of Spray tip penetration for Diesel

Chamber pressure, bar

1 2 3 4 5

Diesel 14.28 14.85 15.25 15.57 15.83

Biodiesel

(JOME)

14.83 15.1 15.64 15.93 16.15

Experimental values of spray cone angle (θ)

SPRAY CONE ANGLE

When the chamber pressure is low the fuel droplets have higherinitial velocity due to lower shear resistance from ambient chamber air density hence the fuel droplets travel faster alongthe axis than in the radial direction, therefore the cone angle ofthe test fuels are lowest at chamber pressure of 1 bar. The spray cone angle for diesel is lower than biodiesel because it

travels faster along the axis rather than the radial direction.

Sauter mean diameter (SMD)

• The quality of the atomization of a liquid spray can be estimated on the medium diameter of the droplets.

• A determined medium diameter represents the equivalent diameter that characterizes the entire group of droplets of the spray.

• Medium diameter is that which defines the characteristics of a population of drops presents in a sample.

Sauter mean diameter (SMD)…

• Elkotb [10] suggested a SMD correlation involving variations in viscosity, density and surface tension.

• Ejim et al [11] suggested that SMD correlation by Elkotb was also applicable to biodiesel which is given by the equation

SMD = 6156 ѵ0.385σ0.737ρf

0.737ρg0.06∆p-0.54 (µm)

σ - Surface tension, N/mѵ - Kinematic viscosity, m2secρf - Density of fuel, Kg/m3

ρg - Density of chamber gas (air), kg/m3

∆P - Difference between injection pressure and chamber pressure (bar)

Estimated SMD for JOME and diesel for various Chamber pressures.

SMD variation

• With injection pressure kept constant at 230 bar, JOME has greater SMD when compared to diesel.

• When the ambient air pressure in the chamber is increased from 1,2,3,4 and 5 bar, SMD also increases.

• The physical properties of liquid fuel that affect its atomization in the process of combustion are viscosity, density and surface tension.

SMD variation …

• The higher viscosity, surface tension and density are responsible for larger values of SMD for JOME.

• The viscosity is regarded to have highest contribution to the change in SMD.

• High viscosity suppresses the instabilities required for the fuel jet to break and thus delays atomization.

• An increase in fuel density adversely affects atomization whereas high surface tension opposes the formation of droplets from liquid fuel.

Spray volume

To understand fuel-air mixing, the spray volume is estimated.

Fuel spray is assumed to consist of a cone and half a sphere, thus

spray volume is described by the correlation suggested by

Delacourt et al. [12] which is given by323

))2/tan(1(

))2/tan(21(

2tan)(

3

1)(

tStV

Spray volume …

Spray volume … With the increase of ambient density, spray

volume is decreased remarkably due to the increased spray angle.

High ambient density supplies strengthened resistance to fuel spray

inhibits spray development in axial direction, which results in a wide spray angle.

droplet velocity which was high initially, retards near the tip of the spray leading to reduction in spray volume.

Conclusions The experimental setup has been developed to

study the spray characteristics of diesel and bio diesel in a constant volume chamber.

From the images - spray angle , spray length and SMD were calculated.

The experimental results shows that as the chamber pressure is increased, the spray

cone angle and Sauter Mean Diameter (SMD) increased for JOME

but the spray tip penetration and spray volume decreased.

Conclusions ….

When compared to diesel, JOME gives longer spray tip penetration and larger SMD due to the higher density, viscosity and surface tension of the fuel.

From the results we can see that the values obtained for diesel and bio diesel are not exactly the same but the values still lie within the permissible limits.

Therefore diesel can be completely replaced with biodiesel but it will reduce the performance of the engine.

Effect of injection pressure(180 to 230 bar)

• Spray penetration length increases for biodiesel with increase in injection pressure.

• Reason: increase in fuel viscosity prevented the breaking of spray jet, resulting in an increase in the size of the spray droplets.

• Viscosity and surface tension are higher for biodiesel

• Spray angle increases with increase in injection pressure for biodiesel.

CONCLUSION….

Overall, biodiesel, especially for the blends with a small portion of biodiesel, is technically feasible as an alternative fuel in CI engines with no or minor modifications to engine.

For environmental and economic reasons, their popularity may soon grow.

However, more researches and development in biodiesel resources and engine design are needed.

THANK YOU