In-Cylinder Pressure Characteristics of a Cl Engine Using Blends of Diesel Fuel and Methyl Esters of Beef Tallow’ Yusuf Ali, Milford A. Hanna and Joseph E. Borg2 STUDENT MEMBER MEMBER ABSTRACT A Cummins N14-410 diesel engine was operated on twelve fuels produced by blending methyl tailowate, methyl soyate and ethanol with No.2 diesel fuel. Engine in- cylinder pressure data were used to evaluate engine performance. Peak cylinder pressures for each fuel blend at all engine speeds were lower than peak pressure for diesel fuel with the exception of the 80 % diesel, 13 % methyl tallowate, and 7 % ethanol; and the 80 % diesel, 6.5 % methyl tallowate, 6.5 % methyl soyate and 7 % ethanol blends. The indicated mean effective pressure (IMEP) values for ail fuel blends were less than for diesel fuel. The differences in lMEP values correlated with differences in power output of the engine. Similarly, maximum rates of pressure rise for most fuel blends were less than for diesel fuel. It was concluded that the fuel blends used in this study would have no detrimental long term effects on engine performance, engine wear and knock. KEYWORDS: Methyl tallowate, methyl soyate, biodiesel, ethanol, Cummins engine, peak pressure, indicated mean effective pressure, rate of pressure change. ‘Journal Series Number 11072 of the University of Nebraska Agricultural Research Division. ‘The authors are: Yusuf Ali, Graduate Research Assistant, Milford A. Hanna, Professor and Director, Industrial Agricultural Products Center, and Joseph E. Borg, Graduate Research Assistant, Department of Bological Systems Engineering, University of Nebraska-Lincoln, Lincoln, NE 68583-0726.
Transcript
In-Cylinder Pressure Characteristics of a Cl Engine Using Blends of Diesel Fuel and Methyl Esters of Beef Tallow’
Yusuf Ali, Milford A. Hanna and Joseph E. Borg2 STUDENT MEMBER
MEMBER
ABSTRACT
A Cummins N14-410 diesel engine was operated on twelve fuels produced by
blending methyl tailowate, methyl soyate and ethanol with No.2 diesel fuel. Engine in-
cylinder pressure data were used to evaluate engine performance. Peak cylinder
pressures for each fuel blend at all engine speeds were lower than peak pressure for
diesel fuel with the exception of the 80 % diesel, 13 % methyl tallowate, and 7 % ethanol;
and the 80 % diesel, 6.5 % methyl tallowate, 6.5 % methyl soyate and 7 % ethanol blends.
The indicated mean effective pressure (IMEP) values for ail fuel blends were less than for
diesel fuel. The differences in lMEP values correlated with differences in power output of
the engine. Similarly, maximum rates of pressure rise for most fuel blends were less than
for diesel fuel. It was concluded that the fuel blends used in this study would have no
detrimental long term effects on engine performance, engine wear and knock.
KEYWORDS: Methyl tallowate, methyl soyate, biodiesel, ethanol, Cummins engine, peak pressure, indicated mean effective pressure, rate of pressure change.
‘Journal Series Number 11072 of the University of Nebraska Agricultural Research Division.
‘The authors are: Yusuf Ali, Graduate Research Assistant, Milford A. Hanna, Professor and Director, Industrial Agricultural Products Center, and Joseph E. Borg, Graduate Research Assistant, Department of Bological Systems Engineering, University of Nebraska-Lincoln, Lincoln, NE 68583-0726.
INTRODUCTION
Interest in cleaner burning fuel is growing worldwide and reduction in exhaust
emissions from the internal combustion (IC) engine is of utmost importance. It is widely
recognized that alternative diesel fuels produced from vegetable oils and animal fats can
reduce the exhaust emissions from compression ignition (Cl) engines without significantly
affecting engine performance (Ali et al., 1995a). Schumacher et al. (1993) reported a
reduction in -NOx emissions when a diesel engine was fueled with 10 to 40 % (v/v)
soydiesel and diesel blends as compared to 100 % diesel or 100 % soydiesel. They also
reported a reduction in engine exhaust opacity with increasing soydiesel in the soydiesel
and diesel fuel blend.
Ali et al. (1995a) reported no difference in power output with different blends of
diesel fuel, methyl tallowate, methyl soyate and ethanol. Further, CO, CO,, O2 and NOx
emissions were not affected by the blends used, but hydrocarbon (HC) emissions were
significantly lower with an 80:13:7 % (v/v) blend of diesekmethyl tallowate:ethanol; the
recommended blend for minimum emissions as compared with No.2 diesel fuel.
Pollutant emissions reduction from diesel engines requires detailed knowledge of
the combustion process. However, the complex nature of the combustion process in a
diesel engine makes it difficult to understand the events occurring in the combustion
chamber which determine the emissions of exhaust gases including CO, CO,, HC and
NO,. Several studies have reported on the effects of fuel and engine parameters on diesel
exhaust emissions. Kittleson et al. (1988) conducted in-cylinder and exhaust soot mass
measurement on a single-cylinder conversion of a 4-cylinder, direct injection (DI) diesel
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engine using a sampling system which allowed dumping, diluting, quenching and collecting
the entire contents of the cylinder on a time scale of about 1 ms. Soot mass was observed
shortly after top dead center (ATDC) which reached a peak between 15 and 30” crank
angle (CA) ATDC. After reaching its peak value, soot concentration decreased with
increasing CA and approached exhaust levels by 40 - 60 “CA ATDC. They concluded that
0, availability, late in the cycle, was a critical factor in determining exhaust soot
concentrations.
Barbella et al. (1989) studied the formation and oxidation of soot, light and heavy
hydrocarbons, CO, CO,, and NO, during the combustion cycle of a DI diesel engine. They
observed that the concentrations of heavy hydrocarbons decreased during the early stages
of the combustion cycle. Maximum soot formation occurred during the diffusion burning
phase in as little as 10 “CA ATDC reaching a concentration of 1.3 mg/NL, after that the
soot formation decreased slowly in 40 “CA ATDC up to 0.05 mg/NL in the exhaust.
To understand the complete combustion process and events occurring in the
combustion chamber in-cylinder pressure data must be analyzed. This project was
undertaken to determine cylinder pressure, rate of pressure change and their respective
locations on selected biofuels and diesel blends using a Cummins N14-410 diesel engine.
MATERIALS AND METHODS
Engine and Instrumentation: A 1991 Cummins Nl4-410 DI diesel engine was used in
this research. Specifications of the engine are presented in Table 1.
The engine was coupled to an Eaton 522 kW dynamatic eddy current dry gap
dynamometer (EATON Power Transmission Systems, Eaton Corp., Kenosha, WI) with a
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DANA 1810 coupler. Engine torque was measured with a load cell and Daytronic system
IO integrator (Day-tronic Corp., Miamisburg, OH), and speed was measured using a 60
tooth sprocket and magnetic pickup attached to the dynamometer. Engine torque and
speed were controlled with an Eaton Dynamatic dynamometer controller in conjunction
with a Jordan controls throttle controller.
In-cylinder pressure measurement were made using an AVL QH32C quartz
pressure transducer connected to a KISTLER Model 5004 Dual Mode Charge Amplifier.
The pressure transducer was located in the head of cylinder No.1 close to the center of the
cylinder. Crank angle was measured using a Gurley Precision Instruments Model 8225
3600-CDSD-KZ rotary shaft encoder. The optical shaft encoder was mounted to the front
of the engine and connected to the crank shaft with a flexible coupler. The encoder was
connected to a Super-Flow Corp. SF-1815 Engine Cycle Analyzer Power Supply that
supplied both power and signal conditioning for the crank angle and top dead center
signals. The charge amplifier and power supply outputs were connected to a SuperFlow
Corp. DAB 500 high speed data acquisition board placed in a 66 MHZ 80486 based PC.
The data were collected using a ECA911 SuperFlow Corp. software package.
Specifications for pressure transducer, charge amplifier and shaft encoder are presented
in Table 2.
Fuels : Blends of high sulfur (0.24 Oh) No.2 diesel fuel, methyl tallowate, methyl soyate and
fuel ethanol were made and tested. Specific blend compositions are given in Table 3.
The methyl tallowate and methyl soyate were produced by Proctor and Gamble Co. of
Kansas City, KS and purchased from lnterchem, Inc. of Kansas City, MO. Physical
properties of methyl tallowate, methyl soyate and their blends with diesel fuel and ethanol
were reported by Ali et al. (1995b).
Testing Procedure : The charge amplifier and the SuperFlow power supply were turned
on two hours before collecting data to allow the instruments to stabilize. The engine was
started and warmed-up, at low idle, long enough to establish recommended oil pressure
and was checked for any fuel, oil, water and air leaks. The speed was then increased to
1600 rev/min and sufficient load was applied to raise the coolant temperature to 71 “C.
After completion of the warm-up procedure, the intake and exhaust restrictions were set
at rated engine speed (1800 rev/min) and full load, and from then on were not adjusted.
The test procedure consisted of an eight mode steady state emissions test sequence
followed by four full load test points at different speeds to complete the torque and power
map. Table 4 presents the speeds and loads used for the different tests. The testing was
done in the Nebraska Power Laboratory at the University of Nebraska-Lincoln.
The engine was run at each speeds and load combination for a minimum of 6 min
and data were collected during the last 2 min of operation. Pressure data were collected
for all 12 speed and load combinations. For this paper only data taken while the engine
was at its maximum constant load at a given speed were used. The data points were
taken at engine speeds of 1100,1200,1400,1600, 1800 and 1900 rev/min and full loads.
Data were collected over 450 engine cycles at each point and averaged.
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RESULTS AND DISCUSSION
In-cylinder pressure and change in pressure with respect to crank angle were
determined and analyzed for different fuel blends. The crank angle at which peak pressure
developed inside the cylinder was determined for each fuel blend and was compared with
No.2 diesel fuel in terms of peak pressure magnitude and crank angle location. Factors
that affect peak pressure include compression ratio, load or volumetric efficiency, and
influences of combustion chamber design on combustion duration and heat transfer. So
do fuel specific heat, energy content, and quality. Abnormal phenomena which affect
maximum cylinder pressure are knock and partial burn.
The purpose of an engine is to generate internal pressure which can be used to do
work. Therefore, high pressures are desirable. However, excessively high and erratic
pressures are a source of potential damage and should be avoided. Knowledge of the
limits of pressure and maximum rate of pressure change can be used to determine if fuels,
other than diesel fuel, can cause engine damage or failure.
Pressure vs Crank Angle : This relationship gives a gross indication of engine
performance. It answers questions related to engine knock, the location of peak pressure;
and the value of the peak pressure.
The values of peak pressure developed in the engine and the crank angle location
at peak pressure (LPP) for the fuel blends at different engine speeds are presented in
Table 5. Representative graphs showing the maximum and minimum pressure with
respect to crank angle for peak torque and rated speed are shown in Figs. 7 and 2.
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It was observed (Table 5) that in-cylinder peak pressure increased as engine speed
increased from 1100 to 1200 rev/min and decreased as the speed was increased further.
Maximum peak pressure was developed at 1200 rev/min, the engine speed at which peak
torque was produced. LPP also decreased with increasing engine speed (Table 5). LPP
at 1100 rev/min was in the range of 10.5 to 11 “CA ATDC for all fuel blends and was
reduced to 3 to 5 “CA ATDC as engine speed increased to 1900 rev/min. The pressure
curve shapes for all fuel blends at all engine speeds were similar to that of No.2 diesel
fuel, which had peak pressures of 15 and 14 MPa at peak torque and rated speed,
respectively.
At 1200 rev/min engine speed, the peak pressure for 80:20,70:30 and 60:40% (v/v)
blends of diesel:methyl tallowate were all within 2% of that for No.2 diesel fuel. The LPP
for the 80:20, 70:30 and 60:40 “/“(v/v) blends of diesel:methyl tallowate were 10.6, 10.8
and 10.8 “CA ATDC, respectively, as compared to 10.4 “CA ATDC for No.2 diesel fuel.
Replacing the methyl tallowate in the above blends with fuel ethanol and methyl soyate
reduced the peak pressure by as much as 6.5%. Reductions in peak pressure were
consistent with the reductions in the energy contents of the blends as compared to No.2
diesel fuel (Ali et al., 1995a). Ali et al. (1995b) also reported a significant reduction in
power output when diesel and methyl tallowate were blended with ethanol. LPP with these
blends were not markedly affected. A comparison of peak pressure, developed at peak
torque conditions, for No.2 diesel fuel showed an 8.86 % drop in peak pressure for the
65:35 % (v/v) methyl tallowate:ethanoI blend and a 6.93 % drop in peak pressure when 50
% of the methyl tallowate was replaced with methyl soyate. The LPP’s of these blends
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were 10.2 and 10.4 “CA ATE, respectively.
At rated engine speed of 1800 rev/min, the peak pressures for 80:20, 70:30 and
60:40% (v/v) diesehmethyl tallowate blends were within 1% of that for No.2 diesel fuet.
The LPP for the 80:20 and 70:30 blends was 7.0 “CA ATDC; the same as observed for
No.2 diesel fuel. The LPP for the 60:40 blend was 7.6 “CA ATDC. When the methyl
tallowate was replaced by fuel ethanol and methyl soyate the peak pressure was reduced
by as much as 3.85% except in the cases of the 80:13:7% (v/v) blend of diesel:methyl
tallowate:ethanol and the 80:6.5:6.5:7% (v/v) blend of diesel:methyl tallowate:methyl
soyate:ethanol, in which the peak pressure was increased by 0.55% and 4.87%,
respectively. LPP’s for all fuel blends were not significantly different from that for No.2
diesel fuel. The increase in peak pressure with the 80:6.5:6.5:7 % (v/v) blend of
diesehmethyl tallowate:methyl soyate:ethanol was expected as the energy content of this
blend was more than that of the 80:13:7 % (v/v) blend as reported by Ali et al. (1995b).
A comparison of No.2 diesel fuel with a 65:35 % (v/v) methyl tallowate:ethanol blend and
a 32.5:32.5:35 % (v/v) methyl tallowate:methyl soyate:ethanol showed that for both fuels
peak power dropped by 9.89 % and LPP increased to 9.2 “CA ATDC as compared to 7.2
“CA ATDC for No.2 diesel fuel.
Similar trends were observed at all other engine speeds. Looking at the magnitude
of the peak pressures for the blends as compared to No. 2 diesel fuel, it was concluded
that since the peak pressures were less than that for No.2 diesel fuel, there should have
been no effect on engine durability. In two cases, i.e. with the 80:13:7 % (v/v) blend of
diesel:methyl tallowate:ethanol and the 80:6.5:6,5:7 % (v/v) blend of dieselmethyl
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tallowate:methyl soyate:ethanol, the peak pressures were higher than No.2 diesel fuel, but
the magnitudes of the increases were too small to cause any problem related to knock,
combustion or partial burn with engine performance.
Indicated Mean Effective Pressure: The indicated mean effective pressures (IMEP) of
the cycles, calculated using SuperFlow Software, are presented in Table 6. IMEP is
defined as the indicated average constant pressure exerted on the piston during the
expansion stroke which will produce the same amount of work as the actual pressure
during the compression and expansion strokes. Since the IMEP is related to the power
output of the engine, differences in the IMEP can be compared with differences in power
output at a given engine speed.
At 1200 rev/min engine speed, the IMEP values for the 80:20, 70:30 and 60:40%
(v/v) blends of dieseLmethyl tallowate were within 2.5% of that for No.2 diesel fuel. These
results were consistent with the peak pressure results with the same blends. The
reduction in IMEP values was as much as 4.28% when part of the methyl tallowate was
replaced with ethanol and methyl soyate. A comparison of IMEP values at peak torque
conditions for No.2 diesel fuel, the 65135% (v/v) blend of methyl tallowate:ethanol andthe
32.5:32.5:35% (v/v) blend of methyl tallowate:methyl soyate:ethanol showed 11.5% and
9.15% drops in JMEP values, respectively.
At rated speed of 1800 rev/min, the IMEP values for the 80:20, 70:30 and 60:40%
(v/v) blends were all within 1% of that for No.2 diesel fuel. Once again when methyl
tallowate was replaced by fuel ethanol and methyl soyate, the reduction in IMEP was as
much as 4.5%. Ali et al. (1995c) reported that for each 10 % replacement of diesel fuel
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with methyl tallowate:ethanol there was a 1 .l % reduction in power output at rated engine
speed. The reductions in the IMEP values correlated well with power reductions reported
by Ali et al. (1995c), except for the 80 % blend which showed a 1.07% IMEP decrease
instead of an expected 2.2 % decrease. A comparison of No.2 diesel fuel with 65:35%
(v/v) methyl tallowate:ethanol and 32X1:32.5:35% methyl tallowate:methyl soyate:ethanol
showed that the IMEP values decreased by 16.6 and 15.2%, respectively.
Derivative of Pressure with respect to Crank Angle : This analysis, which is simply the
derivative of the pressures shown in Fig. 1, indicates how rapidly pressure changes and
helps identify potentially damaging combustion conditions. After correlating the observed
value of the maximum rate of pressure rise with the engine hardware, an engine
manufacturer can establish a limiting maximum value which will ensure acceptable engine
life.
The values of the peak rate of change of pressure in the engine and their crank
angle locations for all fuel blends at different engine speeds are presented in Table 7.
Representative graphs showing the development of change in pressure with CA for engine
speed at peak torque and rated speed are shown in Figs. 3 and 4, respectively. The points
in the combustion strokes at which the derivatives were equal to zero in Figs. 3 and 4
correspond to the points of maximum pressure indicated in Figs. 1 and 2, respectively.
Table 7 shows that in-cylinder pressure change was maximum at an engine speed
of 1100 rev/min and decreased as engine speed was increased to 1200 rev/min and then
increased as engine speed was further increased to 1600 rev/min, the speed at which
maximum power was produced. Further increasing engine speed again decreased the
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peak value of pressure change. The location of maximum pressure change with CA also
shifted from 0.0 to 0.4 “CA ATDC to 13 to 13.6 “CA BTDC. The shapes of all pressure
change curves were the same as that for No.2 diesel fuel. No.2 diesel fuel had a peak
changes of pressure of 361 kPa, 385 kPa, and 374 kPa at engine speeds of 1200 and
1600 rev/min and at rated engine speed of 1800 rev/min, respectively. The locations
shifted from 0.2 “CA ATDC to 13.6 “CA BTDC and 13.8 “CA BTDC at the above engine
speeds, respectively.
At 1200 rev/min engine speed, peak values of change in pressure with crank angle
for the 80:20,70:30 and 60:40% (v/v) blends of diesel:methyl tallowate were within 2% of
that for No.2 diesel fuel. The location of these points were 0.2 “CA ATDC, 11.2 “CA
before top dead center (BTDC) and 2.4 “CA BTDC for 80:20, 70:30 and 60:40 blends,
respectively. When the methyl tallowate was replaced by fuel ethanol and methyl soyate,
the peak values of change in pressure with CA increased by as much as 3.88% without
significantly affecting their locations. A comparison of No.2 diesel with 65:35 % (v/v)
methyl tallowate:ethanol and 32.5:32.5:35 % (v/v) blend of methyl tallowate:methyl
soyate:ethanol showed increases in peak values of change in pressure with CA of 3.88
and 2.22 %, respectively, and changes in location to 0.0 “CA TDC for both blends.
At an engine speed of 1600 rev/min, where peak power was produced, the peak
value of change in pressure was maximum within the operating range of 1200 to 1800
rev/min. The peak values of change in pressure for 80:20, 70:30 and 60:40% (v/v) blends
of diesel:methyl tallowate were within 1.55% of that for No.2 diesel fuel. Their locations
were more or less the same as that for diesel fuel. When methyl tallowate was replaced
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by fuel ethanol and methyl soyate the reduction in peak values was as much as to 6.75%.
Their locations were the same as that for diesel fuel. A comparison of No.2 diesel fuel with
the 65:35 % (v/v) blend of methyl tallowate:ethanoI and the 32.5:32.5:35 % (v/v) blend of
methyl tallowate:methyl soyate:ethanoI showed that there was an 11.4 % decrease in the
peak value of change in pressure with CA for both blends. Once again, the locations of
the peak value for both blends were 13.6 “CA BTDC, the same as for diesel fuel.
At rated engine speed of 1800 rev/min, the peak values of change in pressure with
CA for the 80:20, 70:30 and 60:40 % (v/v) blends of diesel:methyl tallowate were within
1.5% of that of No.2 diesel fuel. The locations of the peak changes in pressure were
shifted to 14.6, 14.4 and 14.0 “CA BTDC, respectively as compared to 13.8 “CA BTDC for
No.2 diesel fuel. When methyl tallowate was replaced by fuel ethanol and methyl soyate,
the values of change in pressure with CA decreased by as much as 5.88%. The locations
of the peak change in pressure for all three fuel blends were around 14.2 “CA BTDC. A
comparison of No.2 diesel with 65:35 % (v/v) methyl tallowate:ethanoI and 32.5:32.5:35%
(v/v) methyl tallowate:methyl soyate:ethanol showed that there was 12.3 % decrease in
peak value of change in pressure with CA for both blends. The location of the peak
change in pressure for both blends was 14 “CA BTDC.
Looking at the performance of the engine in terms of peak value change in pressure
with CA, it can be concluded that there were minor differences in the peak values. In most
cases, the peak value of change in pressure were less than that for No.2 diesel fuel.
These small differences in the rate of change in pressure should have no long term effect
on engine performance, engine wear and knock.
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CONCLUSIONS
Engine cycle analysis was conducted to analyze in-cylinder pressure data to
estimate peak cylinder pressure and rate of change of pressure. Peak cylinder pressures
for each fuel blend at all engine speeds were lower than the peak pressure with No.2
diesel fuel except at 1800 rev/min engine speed with the 80:13:7 % (v/v) blend of
diesel:methyl tallowate:ethanol and 80:6.5:6.5:7 % (v/v) blend of diesel:methyl
tallowate:methyl soyate:ethanol. These points peak pressures were 0.55 and 4.87 %
higher than diesel fuel. These increases were not high enough to cause any cylinder and
piston damage, due to over pressure conditions. Indicated mean effective pressures
(IMEP) for all fuel blends and engine speeds were less than the IMEP for No.2 diesel fuel.
The differences in IMEP values corresponded with differences in power output of the
engine. The maximum rate of pressure rise for most fuel blends were less than the
maximum rate of pressure rise for No.2 diesel fuel. In some cases, the maximum rate of
pressure rise was higher than diesel fuel but it was never more than 5 %. The location of
the maximum pressure rise was close to the location of maximum pressure rise for No.2
diesel fuel.
ACKNOWLEDGMENTS
The authors gratefully acknowledge the contributions of Kevin G. Johnson, Lab
Technician, Nebraska Power Laboratory, University of Nebraska-Lincoln for engine
operation, data collection and analysis and Dr. Louis Leviticus, Professor of Biological
Systems Engineering and Engineer-in-Charge of test and development, Nebraska Power
Lab, University of Nebraska-Lincoln for making the power testing laboratory available.
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REFERENCES
Ali, Y., Eskridge, K.M. and Hanna, M.A. 1995a. Testing of alternative diesel fuel from tallow and soybean oil in Cummins Nl4-410 diesel engine. Bioresource Technology (accepted).
Ali, Y., Hanna, M.A. and Cuppett, S.L. 1995b. Fuel properties of tallow and soybean oil ester. JAOCS (accepted).
Ali, Y., Hanna, M.A. and Borg, J.E. 1995c. Optimization of diesel:methyl tallowate:ethanol blend for reducing emissions from diesel engine. Bioresource Technology (accepted).
Barbella, R. Bertoli, C. Ciajolo, A. D’Anna, A. and Masi, S. 1989. In-cylinder sampling of high molecular weight hydrocarbons from a 0.1. light duty diesel engine. SAE paper No. 890437. Society of Automotive Engineers, Warrendale, PA.
Kittelson, D.B., Pipho, M.J., Ambs, J.L. and Luo, L. 1988. In-cylinder measurements of soot production in a direct injection diesel engine. SAE paper No. 880344. Society of Automotive Engineers, Warrendale, PA.
Schumacher, LG., Borgeft, S.C. and Hires, W.G., Spurfing, C., Humphrey, J.K. and Fink, J. 1993. Fueling diesel engines with esterified soybean oil - project update. ASAE paper No. MC93- 10 1. American Society of Agticdturai Engineers, St. Joseph, MI 49085.
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‘able 1. Engine Specificati ns.
Specifications Cummins N14-410 diesel engine
6 cylinder, Q-stroke, direct injection Type of engine
