2. Performance Characteristics of Biodiesel Mixtures In A Variable Compression Ratio
Engine with Cr 17
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Cite this Article: Biju Cherian Abraham and Chindhu Prasad,
Performance Characteristics of Biodiesel Mixtures In A Variable Compression
Ratio Engine with Cr 17. International Journal of Mechanical Engineering
and Technology, 6(8), 2015, pp. 96-104.
http://www.iaeme.com/currentissue.asp?JType=IJMET&VType=6&IType=8
_______________________________________________________________
1. INTRODUCTION
The large increase in industrialization and motorization in recent years has resulted in
great demand for petroleum products. Energy demands increases as the combustion of
fossil fuels increases and fossil fuels are limited, research is directed towards
alternative fuels. The increase in crude oil import affects the country’s economy and
its development. The acid rain, global warming and health hazards are the results of ill
effects of increased polluted gases like SOx, CO and particulate matter in atmosphere.
The most modern scientific studies are researching on nature friendly inventions and
to preserve nature for future life. Biodiesel is an alternative fuel similar to
conventional or ‘fossil’ diesel. Today’s diesel engines require a clean burning with a
stable fuel that performs well under the variety of operating conditions. Biodiesel is
the only alternative fuel that can be used directly in any existing unmodified diesel
engine. Because it has similar properties to diesel fuel, biodiesel can be blended at any
ratio with diesel fuel.
The present study focuses on the effect bio diesel blend s at various compression
ratios in a compression ignition engine. A.Javidialesaadi and S. Raeissi investigates
the pre-treatment step of biodiesel production from acid oils. In this work the effects
of methanol-to-oil ratio, the amount of catalyst and time on the progress of the
reaction are studied. Evangelos studied the exhaust emissions of diesel engines
operating under transient conditions with biodiesel fuel blends. Irrespective of driving
cycle type, the NOx emission penalty and the PM benefit with biodiesel seem to
increase for more aggressive cycles/driving patterns. Moreover, biodiesels produced
from unsaturated feedstocks tend to increase the NOx emission liability, such
correlation has been established for the emitted PM, HC or CO. Hifjur Raheman
studied Combustion characteristics and emissions of a compression ignition engine
using emulsified jatropha biodiesel blend. With increasing percentage of water,
ignition delay was longer at higher engine loads. Reductions in emission were
observed for the emulsified fuel compared to JB10. Emulsified biodiesel can be
recommended for use in place of biodiesel. Jincheng Huang studied the performances
and emissions of a diesel engine is carried out using two different biodiesels derived
from Chinese pistache oil and jatropha oil compared with pure diesel. The results
shows brake thermal efficiencies of the engine run by the biodiesels are comparable to
that run by pure diesel, with some increases of fuel consumptions. It is found that the
emissions are reduced to some extent when using the biodiesels. Also the engine
performance and emissions by Chinese pistache are similar to that run by jatropha
biodiesel.
2. EXPERIMENT
Biodiesel is produced from pure jatropha and rubber seed oil. These feedstock are
purchased from local market. The biodiesel production is done by trasesterification
method. Methanol and sodium hydroxide is used for this process. The experiment
compare the characteristics of pure diesel (100%), J20 ( 20% jatropha + 80% Diesel),
3. Biju Cherian Abraham and Chindhu Prasad
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JR20 (10% jatropha + 10% rubber seed + 80% Diesel). The characteristics include
both the performance and emission. The test is conducted at a compression ratio of 17
in a VCR engine.
Table 1 Properties of Fuel
Properties Jatropha oil
Jatropha
biodiesel
Rubber seed
oil biodiesel
Rubber
seed oil
Diesel
Density, g/ml 0.920 0.865 0.837 0.91 0.841
Viscosity @
400
C, cSt
3.5 5.2 3.12 7.64 4.5
Calorific Value,
MJ/kg
39.7 39.2 38.20 37.5 42.0
Flash point, 0
C 240 175 128 65 50
Cloud point, 0
C 16 13 5 5.2 9
Experiments were initially carried out on the engine using diesel as fuel in order to
provide base line data. Initially the engine was started using diesel fuel and allowed to
run for few minutes until to reach steady state; the base line data were taken. Load
was varied from zero loads to full load condition using an eddy current dynamometer
and Emissions and fuel consumption reading were recorded. The engine was started
with biodiesel blends as fuels e the supply either by using a two way valve or a
premixing tank. Once the engine reaches steady state, the emission and fuel
consumption were taken. The same procedure is carried from zero to full load
condition. Similarly same procedures were carried for other fuels to be tested.
Figure 1 Experimental set up
The experimental test set up as shown in “Fig 1” consists of four stroke, constant
speed and single cylinder diesel engine. The engine is water cooled. The test was
conducted in a computerized variable compression ratio multi fuel engine test rig
developed by Legion Brothers. Extensive range of experiment can be done this test
rig. The compression variable from 5:1 to 10:1 for petrol and 14:1 to 20:1 for diesel. It
consists of spark plug, ignition coil, diesel injector, diesel pump and carburetor. It has
facility to export the data to Microsoft excel. A standard air tank is fitted with a
Differential pressure sensor for measuring the Actual volume of air drawn into the
cylinder. The thermocouple and necessary signal conditioner for the measurement of
temperature at various points are suitably provided. The loading of the engine is
4. Performance Characteristics of Biodiesel Mixtures In A Variable Compression Ratio
Engine with Cr 17
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controlled by the computer, hence precise loading is achieved. The test rig is provided
with Eddy Current Dynamometer.
Figure 2 Test Engine, DAQ and Dynamometer
Experiments System has a lot of capabilities such as calculate Actual volume of air,
Calculate Volumetric Efficiency, Calculate specific fuel consumption (SFC),
Calculate brake Thermal Efficiency, Calculate Brake power, Heat Balance chart,
Brake power , Calculate mechanical efficiency, Calculate Frictional Power, Calculate
indicated Power, mechanical efficiency , PV and P-θ diagrams, Estimated End of
Combustion Angle, Gross IMEP, Maximum Heat Release Rate, Maximum Heat
Release rate crank angle, Maximum pressure rise rate, Maximum pressure rise rate
crank angle, Maximum pressure, Maximum pressure crank angle, Calculate Start of
Combustion, Ignition delay, ignition duration can be studied. Measurement of
temperature at different points are Inlet water temperature in calorimeter (range 0-
3000
C), Outlet water temperature in calorimeter (range 0-3000
C), Inlet exhaust gas
temperature in calorimeter (range 0-15000
C), Outlet exhaust gas temperature in
calorimeter (range 0-15000
C), Inlet water temperature to engine (range 0-3000
C) and
Outlet water temperature from the engine cylinder (range 0-3000
C). ‘K ’type
temperature sensor is used for the purpose.
Windows based powerful software for real time data measurement, auto zoom
graphs, analog and digital display of data in the computer, store indefinite no of
graphs for analysis. Facilities to export data to Microsoft excel. The data acquisition
software is developed by legion brothers. The following table shows the specifications
of various components.
5. Biju Cherian Abraham and Chindhu Prasad
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Table 2 Specification
Engine Dynamometer
Make Legion Brothers
Type:
Make (Selectable
by the client)
PowerMagCompression Ratio 5: 1 to 20:1
No of cylinders Single
Cooling Water Cooling Air
Fuel Diesel Load
Measurement
method
Strain Gauge
Speed 1400-1500 RPM
HP 3 to 5HP Max Speed 3000 rev/m
Starting Manual Crank start HP 5 HP
Lubrication Forced Coupling Type Direct
3. RESULTS AND DESCUSSION
3.1. Engine performance
The combustion analysis tests are presented at various loads with a speed of 1500
rpm. The cetane number (CN) of biodiesel derived from the jatropha is 54 and Rubber
seed is 51 which is slightly higher than diesel which has the value of 49.
Figure 3 Pressure vs Crank Angle
Ignition delay is an important combustion parameter in diesel engine as it affects
start of combustion, rate of heat release and peak pressure which depends on its
cetane number. The maximum cylinder gas pressure was found to be 53.48 Bar, 43.40
Bar, 45.03 Bar at 0 Kg and 64.68 Bar, 58.87 Bar, 57.86 Bar at 9 Kg for D100, J20 and
JR20 respectively. At all engine loads, combustion starts earlier for biodiesel than for
diesel. This is due to a short ignition delay and advanced injection timing for biodiesel
(because of a higher bulk modulus and higher density of biodiesel). In spite of the
slightly higher viscosity and lower volatility of biodiesel, the ignition delay seems to
be lower for biodiesel than for diesel. The reason may be that a complex and rapid
pre-flame chemical reaction takes place at high temperatures. As a result of the high
cylinder temperature existing during fuel injection, biodiesel may undergo thermal
cracking and lighter compounds are produced, which might have ignited earlier to
0
20
40
60
-500 0 500
PRESSURE
CRANK ANGLE
PRESSURE VS CRANK ANGLE
AT 0 Kg
JR20
J20
D100 0
20
40
60
80
-500 0 500
PRESSURE
CRANK ANGLE
PRESSURE VS CRANK ANGLE
AT 9Kg
JR20
J20
D100
6. Performance Characteristics of Biodiesel Mixtures In A Variable Compression Ratio
Engine with Cr 17
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result in a shorter ignition delay. At lower engine speed the variation is low as
compared to higher loads. As the engine load decreases, the residual gas temperature
and wall temperature decreases, which result in lower charge temperature at injection
time and lengthening the ignition delay.
Figure 4 BR TH Efficiency Figure 5 SFC
The variation of brake thermal efficiency of the engine for J20 and JR20 biodiesel
is shown in “Fig 4” and compared with the brake thermal efficiency obtained with
diesel. At lower brake powers the BTE of biodiesel blend and biodiesel mixtures are
same as that of diesel fuel. The reasons for this improvement of Brake thermal
efficiency is better combustion and better lubricating property of biodiesel. “Fig 6”
compares the specific fuel consumption of diesel and various bio blends. It was
observed that the specific fuel consumptions of the diesel as well as the blends were
decreased with increasing load up to 80% load and then increases. Due to lower
calorific value of biodiesel, for the same power output B20 needed more fuel flow
than diesel as shown, which is also reported by many researchers. At maximum
power, the fuel flow rate of J20 was about 2% higher than diesel.
From the figure it is clear that for jatropha biodiesel blend the volumetric
efficiency is very low. The volumetric efficiency of the diesel engine mainly depends
upon the combustion chamber temperature. The increase in the chamber temperature
increases the intake air temperature and consequently reduces the mass of air drawn in
each cycle thereby decreasing the volumetric efficiency. Biodiesel mixture has higher
volumetric efficiency when compared to biodiesel.
Figure 6 Vol. Efficiency Figure 7 Mech. Efficiency
0
5
10
15
20
25
30
35
0 2 4
BR.TH.EFF.
B. P.
B. P. VS BR. TH. EFFICIENCY
JR20
J20
D100 0
0.1
0.2
0.3
0.4
0.5
0.6
0 2 4
S.F.C.
B.P.
B. P. VS S. F. C.
JR20
J20
D100
80
82
84
86
88
90
0 2 4
VOL.EFF.
B. P.
B. P. VS VOL. EFFICIENCY
JR20
J20
D100 0
10
20
30
40
50
60
70
0 2 4
MECH.EFF.
B. P.
BP VS MECH. EFFICIENCY
JR20
j20
D100
7. Biju Cherian Abraham and Chindhu Prasad
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The variations of mechanical efficiency with compression ratio for various blends
are shown in Figure 7. It has been observed that the mechanical efficiency of the
blends is less which may be due to difference in fuel properties such as viscosity and
density. The mechanical efficiency of the fuel blends is in general very close to that of
diesel.
3.2. Emission
By using this analyzer Carbon monoxide (CO), Hydrocarbon (HC), Nitrogen
oxides (NOx), Carbon dioxide (CO2) and Oxygen (O2) were measured for different
blends biodiesel with standard diesel and analyzed for different loads. Fig 8 shows the
variation of carbon monoxide with changing the load conditions. Generally CO
emissions are affected by start of injection timing, injection pressure, physical and
chemical properties of the fuel used, engine load, speed and improper air fuel mixing.
J20 and JR20 produced lower CO than diesel. Biodiesel contains 10–11% oxygen
content which promotes more complete combustion resulting lower CO emissions.
However, effects of biodiesel on CO emissions vary significantly among vehicles,
engine technology, test cycle, and the feed stocks used to produce the biodiesel.
Figure 8 CO% Figure 9 HC
The variation of hydrocarbon emission with different loads for different blends is
given in Fig.9. The fuel viscosity, fuel spray quality and characteristics also the
incomplete combustion affects the HC emission. At higher loads curve became too
steeper due to the rich fuel air mixture. It is seen that unburnt hydrocarbon emission
increases with that of load for all prepared test fuels. From figure it is understood that
biodiesel produces less HC emission in comparison to that of diesel because of better
combustion of the test fuel and its blend due to presence of oxygen.
Figure 10 NOX Figure 11 CO2%
0
0.05
0.1
0.15
0 2 4
CO%
B.P.
B. P. Vs CO%
JR20
J20
D100 0
10
20
30
40
0 2 4
HCppm
B.P.
B. P. VS HC ppm
JR20
J20
D100
0
100
200
300
0 2 4
NOx
B.P.
B. P. Vs NOx
JR20
J20
D100
0
2
4
6
0 2 4
CO2%
B.P.
B. P. Vs CO2%
JR20
J20
D100
8. Performance Characteristics of Biodiesel Mixtures In A Variable Compression Ratio
Engine with Cr 17
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The production of NOX is significantly influenced by the in-cylinder gas
temperature, availability of oxygen and residence time. The variation of nitrogen
oxide with respect to load for both fuels and their blends are as shown in the graph.
The present test results show that NOX emission increases almost linearly with
increase in engine load which is because of higher cylinder pressure and temperature
at higher loads. Due to higher oxygen content the J20 has highest rate of NOx
production. Proper oxygen content and appropriate temperature is necessary for
complete combustion.
The variation of carbon dioxide emission with different compression ratios are
shown in “Fig 11”. Due to lower calorific value of biodiesel more fuel was needed to
produce the same power and also due to fuel-borne oxygen in biodiesel, more carbon
was oxidized to CO2 than partial oxidation of carbon to CO. JR20 has the highest
level of CO2 emission as shown above. Table shows the values of CO2 emission for
all the fuels at the corresponding brake power.
4. CONCLUSION
The pressure developed in the engine is higher for the diesel as compared to the
biodiesel blends in all loads. The cetane number of the biodiesel is higher than the
diesel, which leads to a higher ignition delay for diesel. Ignition delay for all fuels
decreases as the engine load increases because the gas temperature inside the cylinder
is higher at high engine loads, which reduces the physical ignition delay.
BTE curve shows similar characteristics in lower loads and in higher loads the
biodiesel shows better performance. This may be due to better combustion of
biodiesels and lubricating property.
For biodiesel mixture it can be see that SFC is much higher than that of diesel at
lower BP and closer to diesel at higher brake power due to increased fuel efficiency.
Volumetric efficiency is low for the biodiesel as compared to the diesel. The
biodiesels are oxygen rich fuels, so the requirement of air reduces even under low
volumetric efficiency. The mechanical efficiency is higher for the Biodiesel fuel. As
compared to diesel, fuel blends have improved quality of spray, high reaction activity
in the fuel rich zone and heat loss due to lower flame temperature may be the reason
for increase in efficiency.
CO and HC emission are lower for both J20 and biodiesel mixtures when
compared to diesel due to complete combustion of fuel. The curves are steeper in
higher loads due to rich mixture combustion. The trend can be attributed to the higher
oxygen content of Jatropha biodiesel and biodiesel mixtures due to which complete
combustion takes place inside the cylinder.
It is observed that the CO2 emission of biodiesel is much higher value due to the
complete combustion of fuel.
NOx emission is more for J20 than diesel due to increase in oxygen content
because biodiesel contain many mono-unsaturated and poly-unsaturated fatty acids.
The exhaust temperature is higher for the jatropha biodiesel, which results higher
NOx values.
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