MODELING AND ANALYSIS OF
PERFORMANCE, COMBUSTION AND
EMMISSION CHARACTERISTICS OF
JATROPHA METHYL ESTER BLEND
DIESEL FOR CI ENGINE WITH
VARIABLE COMPRESSION RATIO
S. Abinav Viswanath and V. Dinesh
Department of Mechanical Engineering, St. Joseph’s College of Engineering, Jeppiar Nagar, Old Mahabalipuram Road, Chennai, Tamil Nadu – 600119 , India.
abinav91@gmail.com. S. Arivazhagan and N. Vinayagam
Faculty of Mechanical Engineering, St. Joseph’s College of Engineering, Jeppiar Nagar, Old Mahabalipuram Road, Chennai, Tamil Nadu – 600119, India.
vins7075@gmail.com.
Abstract
An experimental study was conducted on a four stroke single cylinder compression ignition engine to determine the performance, combustion and exhaust emission characteristics under different compression ratio using an alternate fuel. The raw oil from the jatropha seed was subjected to transesterification process and is supplied to the engine as jatropha methyl ester (JME) blended with diesel. The blends used in our paper are 10%, 20% and 30%. We found that the performance of the engine under VCR is maximum at 20% blend for CR18. The fuel consumption is also found to be increased with, a higher proportion of jatropha curcas oil in the blend. But BSFC is low at 20% JME-D. Emission was found to be optimum at CR18 for all blends of the methyl ester. At high engine load, the peak cylinder pressure was found to be higher for 20% JME-D under compression ratio 18. Using STAR CD software, three dimensional simulations are deployed and the results generated are compared against the experimental output.
Keywords: Compression ratio, Compression ignition, Performance, Combustion, Emission, Jatropha blend,
CFD, VCR, alternate fuel .
1.Introduction
With the development of the economy, the importance of IC engines is increasing which is obvious. But the problems of oil shortages and emissions have become a key constraint for the development of IC engine. The researches worldwide show that oil resources are declining and they will be more difficult and expensive to recover. This enhances the development and use of biodiesel. Energy from biodiesel is one of the opportunities that could cover the future energy demands.
preferable to other energy crops. The fuel properties of biodiesel such as kinematic viscosity and specific gravity are found within the limits of BIS standards.
The oil is gained from the jatropha seeds. Then a process named transesterification is carried out on the oil.
Vegetable oil + Methanol Methyl ester + Glycerine (1)
The transesterification process is done using methanol with sodium hydroxide as the catalyst. This results in less viscous jatropha oil ie, methyl ester which is a biodiesel. The other product formed is glycerol which eventually leads to the formation of soap.
The specific gravity of most oils and their methyl esters is higher than that of diesel fuel. This is due to the large molecular mass and chemical structures of vegetable oils (Pramanik, 2002, Grab ski and McCormick, 1998). However, this helps in countering their low heating values in terms of brake specific fuel consumption. The specific gravity of a methyl ester depends on its molecular weight, free fatty acid content, water content and temperature (Saeid et al., 2008). Specific gravity data is essential in modeling combustion process in internal combustions engines and also in evaluating the thermal efficiency of the fuel. The viscosity of typical vegetable oils is 15-20 times higher than that of diesel fuel. The viscosity of biodiesel is slightly greater than that of petro diesel but approximately an order of magnitude less than that of the parent vegetable oil or fat (Dunn R.O. and Knothe G., 2001). This results in fuel flow problems when vegetable oils are used in diesel engines. Viscosity is directly related to the iodine value of a vegetable oil, in that the higher the iodine value the higher the viscosity.
The present research is aimed at exploring technical feasibility of jatropha oil in direct injection compression ignition engine without any substantial hardware modifications. In this work the methyl ester of jatropha oil was investigated for its performance as a diesel engine fuel.Fuel properties of mineral diesel, jatropha biodiesel and jatropha oil were evaluated. Three blends were obtained by mixing diesel and esterified jatropha in the following proportions by volume : 90% diesel +10% esterified jatropha, 80% diesel + 20% esterified jatropha, and 70% diesel + 30% esterified jatropha. Performance parameters like brake thermal efficiency, specific fuel consumption, and brake power were determined. Exhaust emissions like CO2, CO, NOx and smoke have been evaluated.
Over the past decade, CFD modeling was improved to simulate 3D flows, mixture formation, burning and pollutant formation for direct injection engines. In the engine development process, CFD modeling of direct injection engine is used to analyze the interaction between the fuel and the motion of the intake air inside the combustion chamber. In the last years, due to an intense world request, a lot of simulation models have been developed using CFD code. Combustion is described by a single step global chemical reaction. Combustion research is more extensive, diverse and interdisciplinary due to powerful modeling tool like CFD. In CI engine the incylinder multiphase fluid dynamics like fuel spray, chemical reaction kinetics influences the combustion. In past, the diesel ignition and combustion process has been modeled with several diverse models: The eddy dissipation model and its derivatives, extensions of the coherent flame model like PDF time scale models, the RIF model. Recent investigations reported the development of new and trustworthy models for combustion. The combustion model needs to consider scale fluctuations, inhomogeneities in the flow field, wall effects and turbulence level. Amongst, kε, RNG kε and twoscale models of different version were compared. To take account of flow features that are relevant to compressibility and turbulence, the RNG kε demonstrates considerable accuracy, when compared with experimental data. The recognized submodels for CI DI diesel combustion includes spray, droplet break up and collision, combustion and wall interaction. The combustion model gives the quantity of fuel atomized, vaporized and burned. Several studies performed with different CFD codes and methods to investigate spray pattern details of diesel injection and its effects on combustion process. Further, microscale phenomena of spray break up and collision having impact on overall modeling of combustion. The different break up models considering wave instabilities KH and RT mechanism predicted realistic spray.
Nomenclature:
BP Brake power BTE Brake thermal efficiency
CA Crank angle HRR Heat release rate
CO Carbon monoxide HC Hydro carbon
CO2 Carbon dioxide NOx Nitrogen oxides
CPmax Cylinder pressure maximum O2 Oxygen
CR Compression ratio BSFC Brake specific fuel consumption CFD Computational Fluid Dynamics
2. Experimental Setup and procedure
Figure 1 Experimental Setup
The performance, combustion and emission tests were carried out on a four stroke, single cylinder, naturally aspirated, water cooled Kirloskar diesel engine having a power capacity of 3.5 kW. It is connected to an Eddy current dynamometer for loading. Temperature and pressure sensors are installed at the necessary locations in the test setup. The temperature sensors measure temperatures at inlet & outlet of water jacket; calorimeter water and calorimeter exhaust gas. It is also provided with pressure sensors to measure combustion pressure inside cylinder and also to measure the fuel line pressure during injection. An encoder is used to measure the crank angle. The signals from these sensors are interfaced with a computer to an engine indicator to display P–V and fuel injection pressure vs. crank angle plots. The provision is also made for the measurement of volumetric fuel flow. The built in program in the system calculates indicated power, brake power, thermal efficiency, volumetric efficiency and heat balance. The software package is fully configurable and averaged P–V plot and liquid fuel injection pressure diagram can be obtained for various operating conditions. A Qrotech 401 exhaust gas analyzer is used to measure 5 emissions in the engine exhaust. The emissions measured are CO, CO2, O2, HC and NOX.
Table 1- Engine Specifications
Engine
Kirloskar TV1, single cylinder, 4 stroke, water cooled constant speed diesel engine
Rated Power 5.2 KW
Speed 1500 rpm
Bore 87.5 mm
Stroke 110 mm
Dynamometer Arm Length 185 mm
Compression ratio 17.5:1
Crank angle sensor Kubler, pulses per revolution : 360
Cylinder Volume 0.661 litre
Intake valve opens 4.5° BTDC
Inlet valve closes 35.5° ABDC
Exhaust valve opens 35.5° BBDC
Exhaust valve closes 4.5° ATDC
Original fuel injection 18° BTDC
Temperature sensor RTD, Digital PT 100
Table 2- Exhaust emission analyser specifications
Exhaust emission analyser
Model Qrotech 401
No. of emissions measured 5
Range CO: 0 – 9.9 %
CO2: 0 – 20 %
HC: 0 – 9999 ppm O2: 0 – 25 %
Table 3 - Diesel properties
PROPERTIES UNITS DIESEL JME-D
(10%)
JME-D (20%)
JME-D
(30%) JME
CALORIFIC
VALUE kJ/kg 42490 42310 42112 41951 40695
DENSITY (at
40 °C ) Kg/m3 840 842 844 847 863
KINEMATIC VISCOSITY (at 40°C)
C.st. 4.59 4.71 4.83 4.95 5.80
SPECIFIC
GRAVITY 0.84 0.842 0.844 0.847 0.863
The procedure followed during the experiments is given below:
(a) Initially engine was run with neat JME-D 10% blend for the compression ratio of 18 (normal value). Engine was run from no load to 75% of full load condition with an increment of 25% of load in each run.
(b) Once the steady state was reached the parameters such as fuel consumption rate, brake power and the exhaust emissions CO2, CO, O2 NOX and HC were measured.
(c) Performance parameters and the emissions were recorded.
(d) Then the compression ratio was adjusted to 16 by losing the 6 Allen bolt nut provided for clamping the tilt block of the cylinder. Then loosen the nut on the adjuster and rotate the adjuster so that compression ratio can be decreased to 16 which can be indicated by the movement of the CR indicator and the marking is noted. Now after the readings are taken the CR indicator is adjusted to compression ratio 18. Then the same procedure is repeated for 20% and 30% blend. In the present study performance, combustion and emission parameters at different operating loads were discussed.
3. Results and discussion
3.1 Performance Characteristics
3.1.1 Brake Thermal Efficiency (BTE)
Figure 2 shows the relation between the BTE and loads for the JME-D blends of 10%, 20% and 30% with the compression ratio 16. It can be noted that the brake thermal efficiency is high for 20% blend compared to the other blends. This is because of the optimum viscosity of the fuel. While the efficiency is low for 30%, the efficiency for 10% blend is comparatively nearer to the maximum. This can be attributed to reduction in heat loss and increase in power with increase in load.
Figure 2 Load vs. brake thermal efficiency under CR 16
Figure 3 Load vs. brake thermal efficiency under CR 18
3.1.2 Brake specific fuel consumption (BSFC)
Figure 4 shows the variation of fuel consumption with respect to load for 16% blend. It can be inferred from the graph that specific fuel consumption for 20% blend is less. While the BSFC for 10% is nearer to the maximum, the 30% blend shows higher specific fuel consumption.
Figure 4 Load vs. brake specific fuel consumption under CR 16
Figure 5 Load vs. brake specific fuel consumption under CR 18
3.2 Combustion Characteristics
3.2.1 Net heat release rate (NHR)
Figure 6 net heat release rate Vs Crank angle
3.2.2 Max cylinder pressure (CPmax)
Figure 7 shows the variation of cylinder pressure for the compression ratio 16 and compression ratio 18. As the compression ratio decreases the delay period increases due to the reduction in auto ignition temperature. Here also the cylinder pressure is maximum for 20% blend due to the higher cetane number. If the cetane no. increases the delay period becomes less and there is smooth engine operation.For jatropha 20% blend cylinder pressure is 70.73 bar which is the maximum cylinder pressure due to the fact that the total volume of the cylinder is maximum in CR18.
Figure 7 cylinder pressure vs crank angle
3.3. Emission Characteristics
3.3.1. Carbon monoxide (CO)
Figure 8 shows how the carbon monoxide emission varies with load for CR18. The emission for 30% is maximum. Poor mixing, incomplete mixing,less oxygen contentwill be the source for CO emission. The emission for 20% blend is the lowest compared to the three blends. This is due to the fact that oxygen content is more for 20% blend compared to others.
and also due to incomplete combustion. Not only is CO considered an undesirable emission ,but it also represent lost chemical energy. So 20% blend with compression ratio 18 yeilds less emission.
Figure 10 Load vs carbon monoxide under CR 16
Figure 11 Load vs carbon monoxide under CR 18
3.3.2. Carbon dioxide (CO2)
Figure 10 shows CO2 variation for various blends under the compression ratio 16. It can be inferred that the
carbon-di-oxide emission that for 20% blend emission is maximum. This is due to the fact that the oxygen content is more for 20% blend compared to other blends. High oxygen content leads to complete combustion which ultimately results in the CO2 emission.
Figure 12 Load vs. carbon dioxide under CR 16
Figure 13 Load vs carbon dioxide under CR 18
3.3.3. Hydrocarbons (CPmax)
Figure 12 graph shows the variation of hydro carbon for the compression ratio 16. As mentioned ealier it can be found that the emission is maximum for 30% blend. While for 10% blend emission is low and for 20% blend it is nearly equal to 30% blend. This can be attributed to the fact that there is incomplete combustion in 30% blend,low compression ratio and hence the emission is high.
Figure 8 Load vs. hydrocarbon under CR 16
Figure 9 Load vs. Hydrocarbon under CR 18
3.3.4. Oxides of nitrogen (NOX)
Figure 14 shows the variation of oxides of nitrogen with respect to load for compression ratio 16. It can be clearly understood from the graph that the nitrogen oxide emission is maximum for 20% blend due to high exhaust gas temperature. The emission of nitrogen di oxide increases with increase in the concentration of jatropha metyl ester in the blend. But here we can see that the emission is minimum for 30% blend. This is due to the fact that the engine is not modified. Engine modifications have to be done for blends having JME concentration more than 30%.
Figure 14 Load vs nitrous oxide under CR 16
Figure 15 Load vs nitrous oxide under CR 18
4. CFD Validation
4.1. Modelling and Meshing:
Figure 16 Modelling &meshing of combustion chamber in Gambit
4.2. Input for Analysis:
4.2.1. General Inputs:
Inlet valve is selected as pressure inlet while exhaust valve is selected as velocity outlet. Injector position is placed between 2 valves, as per the dimensions of the combustion chamber. Inclination of injector is given as 15 degrees. Time was specified in angles and speed was set to 1500 rpm with initial position of 0 degree.. Boundary conditions: wall type was specified for default boundary region i.e the combustion chamber, while pressure for inlet and velocity type for outlet as shown in figure 17. The start and end of ignition was set at 345 and 370 degree respectively. Emission models for NOX and soot were turned on. The inlet and exhaust had
stagnation pressures of 2 bar, while the inlet air was at a temperature of 303K i.e 27°C. The reaction chosen was
C12H26 + 18.5 O2 →12CO2 + 13H2O (2)
Figure 17 Boundary condition on combustion cylinderz
4.2.2. Models Applied:
of ignition, end of the ignition, start of combustion, end of combustion and the injection pressure and velocity are specified as mentioned already.
4.3.1. Maximum Cylinder Pressure:
The maximum pressure developed inside the cylinder is determined by the quantity of fuel vaporized during the ignition delay and occurs during combustion. Figure 18 clearly shows the pressure distribution inside the cylinder. It can be seen that the pressure increases gradually and is maximum at the bottom. The maximum pressure that the cylinder can withhold is 0.6545E+07. While Figure 19 and Figure 20 depicts the temperature distribution and velocity magnitude distribution within the cylinder respectively.
Figure 18 pressure development in the combustion chamber
Figure 19 temperature distributions in the combustion chamber
Figure 20 velocity magnitude in the combustion chamber
4.4. Validation:
Table 4. Comparison of Theoretical and Experimental data COMPRESSION RATIO THEORETICAL VALUE(BAR) EXPERIMENTAL
VALUE(BAR) ERROR (%)
CR 18 70.73 65.45 7.46
5. Conclusion
There are many different alternative fuel options being developed right now. For those who would like to make a change right now, many of the options are already available and would be suitable for day to day life. But for those of you who would like to stay in the mainstream, the future is looking promising with many alternatives that are inexpensive, efficient, and are environment friendly. By making the right choices and further developing these technologies we have to power to save the planet.
o The jatropha tree is indigenous to India, grow even in draught prone area and abundantly in all
parts of India.
o After Transesterification of jatropha oil, kinematic viscosity and specific gravity are reduced
and calorific value is increased.
o The BTE is higher for B20 fuels which is approximately higher than other blends.
o The BSFC for pure biodiesel is higher than the diesel fuels, how ever in B20 fuel, BSFC is
lower than the diesel fuels and other blends
o NOx Emission is higher for pure biodiesel and is lower for B20 fuel, compared to diesel fuel. o The UBHC, and CO are significantly reduced with biodiesel and its Blends
o Based on the engine performance and emission test, 20% blends of methyl esters with diesel
fuel will better performance and lower emission characteristics compared.
o From the combustion characteristics it is found that the maximum cylinder pressure and net
heat release rate are maximum for 20% JME-D blend for CR 18.
o Using STAR CD software the theoretical and experimental cylinder pressure is validated and
is found to have an error 7.46%.
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