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Green Fuels and their impact on the performance and the
exhaust gases in Diesel Engines
J. TRIANDAFYLLISProfessor in the Department of Vehicle
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Contents1. Introduction.2. Effects on engine performance (these
notes are based on bibliography source 3).
3. Measurements of two cars with diesel engines at the Karel de Grote- Hogeschool.
4. Bibliography.
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1. IntroductionTHE SIGNIFICANCE OF PLANT OILS AS
BIO-FUELS. Bio-fuels are oils derived from plants, such as
sunflower oil, cottonseed oil, and safflower oil. Bio-fuels can be utilized in mixtures with diesel
oil to improve the quality of the vehicle exhaust gases, and thus, to improve the air quality.
The air quality can be improved because the bio-fuels when are burnt, do not produce PAH (polyaromatic hydrocarbons), unburnt hydrocarbons, and products of sulphur.
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2. Effects on Engine Performance
2.1 Heating Value Since a bio-fuel is mixed
with diesel, from now on, let us refer to it as biodiesel.
The most important property of a fuel is its lower heating value (LHV), because it affects the quality of combustion, and thus, the production of power.
The lower heating value of all biodiesels is lower than that of diesel.
FUEL Lower Heating ValuekJ/kg
Number 2 diesel
43357
Sunflower oil methylester
38565
Cottonseed oil
methylester
38926
Frying oil ethylester
37225
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Production of Biodiesel
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2. Effects on Engine Performance2.2 Fuel economy Fuel consumption can be calculated from
the carbon dioxide emissions and an analysis of the fuel carbon content.
It is more accurate to combine CO2 emission measurements with a gravimetric measurement of fuel consumption.
From tests it was found that biodiesel and mixtures of biodiesel with diesel exhibit a fuel economy proportional to their lower heating value.
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2. Effects on Engine PerformanceCycle Biodiesel
% 1988 DDC 6V-92TA (mpg)
1981 DDC 8V-71 (mpg)
CBD Stock 0 3,69 3,59 CBD Stock 20 3,68 3,63 CBD 1,5̊Timing change 20 3,54 3,59 CBD Catalyst 20 3,35 3,18 CBD Timing + Catalyst 20 3,26 3,30
Arterial Stock 0 4,67 3,92 Arterial Stock 20 4,72 3,1 Arterial 1,5T̊iming change 20 4,89 3,93 Arterial Catalyst 20 4,64 3,40 Arterial Timing + Catalyst 20 4,56 3,84
Composite Stock 0 3,70 3,66 Composite Stock 20 3,63 3,52 Composite 1,5T̊iming change 20 3,50 3,63 Composite Catalyst 20 3,34 3,21 Composite Timing + Catalyst 20 3,33 3,43
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2. Effects on Engine Performance
2.3 Torque and Acceleration The torque is related to the energy level of
the fuel. Studies have shown torque reductions for
biodiesel and biodiesel mixtures. Acceleration is also reduced for biodiesel
and biodiesel mixtures. Therefore, horsepower is also reduced.
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2. Effects on Engine Performance Peak torque is not significantly
affected up to 35% biodiesel.% Biodiesel Peak torque, ft-lb
(1200 RPM) 0 1283 0 1279 0 1278 0 1286 20 1275 35 1270 65 1256 100 1210
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2. Effects on Engine Performance2.4.1 Durability studies Engines run with biodiesel mixtures
experience problems caused by 1. The appearance of coke deposits on the
valves caused by low volatility fuel at light loads.
2. Plugged filters and injectors by unreacted mono-, di-, and triglycerides, free fatty acids, methanol and glycerol found in raw plant oils.
3. Pump failure caused by deteriorating seals.
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2. Effects on Engine Performance2.4.2 Elastomer compatibility Many of the problems encountered in the
durability studies are traced to the incompatibility of biodiesels with certain elastomers.
Methylesters cause the swelling of trilobutyldilene and nitrile rubber, a material that is commonly used in automotive seals and gaskets.
Fluorine containing elastomers do not swell at the presence of biodiesels.
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2. Effects on Engine Performance2.4.3 Biodiesel lubricity Fuel lubricity is important because in
many fuel pumps the moving parts are actually lubricated by the diesel fuel itself.
From tests it was shown that soybean and rapeseed oil methylesters have superior lubricity when compared to low sulfur diesels.
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2. Effects on Engine Performance2.5 Emissions Diesel engines are regulated for smoke opacity, total
nitrogen oxides (NOx), total particulate matter less than 10 μm (PM-10 or PM), carbon monoxide (CO), and total hydrocarbon (THC).
The useful diesel engine life is 290.000 miles. The diesel engines must meet the emissions criteria throughout their useful life.
Aldehydes and poly-aromatic hydrocarbons (PAH) are not currently regulated. They may be regulated in the future in order to minimize the amount of toxins in the air.
The quantity of CO and THC derived from diesel engines is generally small. For this reason biodiesel fuels are considered for their impact upon PM and NOx .
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2. Effects on Engine Performance2.5.1 Emissions in two-stroke engines For two-stroke engines without timing
changes or exhaust catalyst, the use of biodiesels cause the following changes in the emissions
1. NOx increases 2. PM, CO and THC decrease3. The soot (solid carbon fraction of PM)
decreases.
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2. Effects on Engine Performance
2.5.1Emissions in two-stroke engines(cont.)As the Oxygen content in the Biodiesel mixture increases, the NOx increases and the PM decreases.
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2. Effects on Engine Performance2.5.1 Emissions in two-stroke
engines (cont.)From dynamometer and chassis tests on two-stroke engines, it was found that
The PM emissions depend on engine wear because worn engines slip oil past the rings to the air intake ports.
The NOx emissions are independent of engine type, injector technology, and wear.
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2. Effects on Engine Performance2.5.1 Emissions in two-stroke engines
(cont.) Retarding the injection timing from 1-4o of older engines
run with soy biodiesel, the emissions of NOx were decreased to the level of the engine run with only diesel. At the same time, the PM emissions increased since the NOx were decreased.
This can be theoretically corrected by the presence of an oxidation catalyst. In practice the catalyst does not “capture” the liquid oil droplets and soot and cannot oxidize them.
The general conclusion is that biodiesel increases NOx and decreases hydrocarbons and CO. PM emissions decrease or stay constant for worn engines.
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2. Effects on Engine Performance2.5.2 Emissions in four stroke-engines
Tests showed a similar behavior on emissions between four- and two-stroke engines.
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2. Effects on Engine Performance2.5.2 Emissions in four stroke-engines (cont.)
However, the NOx emissions rise much slower with increasing oxygen content than in the two-stroke engines. This can be explained from the fact that modern four-stroke engines have sophisticated electronic controls that vary the fuel injection timing and other engine parameters to minimize emissions.
The PM emissions decrease more rapidly in four-stroke than in two-stroke engines. This can be attributed to the fact that four-stroke engines are more efficiently lubricated and thus, have lower liquid oil emissions, typically 30% lower than in the two-stroke.
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2. Effects on Engine Performance2.5.2 Emissions in four stroke-engines
(cont.) The use of an oxidation catalyst yields enhanced
PM emissions reduction. The presence of such catalyst and the use of a biodiesel mixture can reduce the PM emissions by 50%.
One can reduce the NOx emissions by increasing the cetane number or decreasing the aromatics.
Retarding the injection timing produced similar results, except that the NOx emissions were smaller. At the same time the PM emissions increased.
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2. Effects on Engine Performance2.6 Smoke opacity Tests showed that in two-stroke engines
the use of biodiesels did not reduce smoke opacity.
However, the combination of an oxidation catalyst and biodiesel produced a significant reduction in smoke opacity, especially in the lugging mode (lugging: engine at low speed under high load).
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2. Effects on Engine Performance2.7Air toxins The use of biodiesels increases the
emission of liquid oil droplets from the lube oil or from the fuel.
There is a decrease of PAH emissions and in the mutagenic activity of the diesel exhaust with the use of biodiesels.
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3. Measurements at the Karel de Grote-Hogeschool and at TEI of Thessaloniki3.1 Introduction
Measurements were made by the staff of Professor M. Pecqueur on two cars in the Combustion Laboratory in the Department of Industrial Sciences and Technology of the Karel de Grote-Hogeschool, Hoboken, Belgium. Similar measurements were done by the staff of Professor John Triandafyllis in the Department of Vehicles at TEI of Thessaloniki on one car. The cars were run under full load at 30, 50, 90 and 120 km/h speeds.
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Bio-fuels used
Two bio-fuels were chosen to be converted chemically to bio-diesels:
Cottonseed oil, which was produced in Macedonia, Greece.
Used cooking oils which were collected in the city of Antwerp, Belgium.
The conversion to bio-diesels was accomplished by Professor Serge Tavernier in the Department of Industrial Sciences and Technology of the Karel de Grote-Hogeschool, Hoboken, Belgium.
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3. Investigation goals
Performance of the diesel engines run with the bio-diesel mixtures as compared to their performance run only with diesel.
Two fuel temperatures were used, at 20oC and at 40oC in order to investigate the effect of the fuel temperature.
The engines were run at two different values of injection timing, -5o and +5o in order to investigate the effect of the injection timing upon NOx and soot in the exhaust gases.
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Investigation goals
TO COMPARE THE EMISSIONS OF PM, NOx AND CO2 BETWEEN DIRECT AND INDIRECT IGNITION ENGINES FUELED BY THE SAME METHYLESTER MIXTURES.
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TEST VEHICLESCharacteristics VOLVO V70 FORD
TRANSIT FORD
ESCORT Injection diesel direct direct indirect
Engine size, liters 2.5 2.5 1.6 Max Power (kw)
at RPM 103
at 4000 74
at 4000 40
at 4800 Compression
ratio 20.5:1 18.3:1 21.5:1
Turbocharged Yes No No EGR Yes Yes No
Engine management
system
ECU No No
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TEST CONDITIONS IN THE DYNAMOMETER
VOLVO FORD TRANSIENT
FORD ESCORT
Second gear
27 kw at 1780 RPM
26 kw at 1930 RPM
15 kw at 1867 RPM
Third gear
28 kw at 1900 RPM
27 kw at 2050 RPM
15.6 kw at 2091 RPM
Fourth gear
41 kw at 3430 RPM
28 kw at 2730 RPM
20.2 kw at 2749 RPM
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TEST EQUIPMENTEquipment Greek lab. Belgian lab.
Chassis dynamometer
Cartec AHS Prueftechnik
Prefilter Signal 351X Own design Gas Analyzer Andros 6800 Hermann HGA 500 Smoke Meter Bosch Opacimeter
RTM 430 SPX Dieseltune DX 230 Digital Smoke
meter
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PerformanceVOLVO diesel engine
FUEL TEMP. 20C 40C
ENGINE POWER, kW
TORQUE, Nm RPM
ENGINE POWER, kW
MAX.TORQUE, Nm RPM
DIESEL 47 130 3486 46 125 3484 B10COTTON 47 131 3445 48 133 3475 B50COTTON 49 130 3567 48 136 3378 B100COTTON 49 132 3499 49 132 3500 DIESEL 46 125 3484 46 125 3484 B10FR.OIL 49 138 3364 49 138 3364 B50FR.OIL 48 131 3502 48 131 3502 B100FR.OIL 48 134 3444 48 134 3444
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PerformanceFORD diesel engine
FUEL TEMP. 40C
IGNITION TIMING -5o +5o
ENGINE POWER, kW
TORQUE, Nm RPM
ENGINE POWER, kW
MAX.TORQUE, Nm RPM
DIESEL 36 136 2563 38 129 2829 B10FR.OIL 40 149 2515 36 125 2786 B50FR.OIL 40 150 2498 35 118 2862 B100FR.OIL 38 146 2519 37 128 2793
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Effect of fuel temperature
EFFECT OF FUEL TEMP.
050
100150200250300350400450500
0 50 100 150
SPEED, km/h
SOO
T, m
g/m
3
40C-B100COTTON
20C-B100COTTON
40C-B10COTTON
20C-B10COTTON
EFFECT OF FUEL TEMP.
0 100 200 300 400 500 600 700 800 900
1000
0 20 40 60 80 100 120 140 SPEED, km/h
NOx, ppm
20C- B100COTTON 40C- B100COTTON 20C-B10COTTON
40C-B10COTTON
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Effect of injection timing
EFFECT OF INJECTION TIMING at 30 km/h
0200400600800
1000
NOx,
ppm
-55FactoryValue
EFFECT OF INJECTION TIMING at 30 km/h
050
100150
SOO
T, m
g/m
3
-55FactoryValue
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Effect of bio-diesel content
NOx vs. SPEEDFUEL TEMP. 40C
0100200300400500600700800900
1000
0 50 100 150
SPEED, km/h
NO
x, pp
m
DIESELB10COTTONB20COTTONB30COTTONB40COTTONB50COTTONB100COTTON
SOOT vs. SPEEDFUEL TEMP. 40C
0100200300400500600700
0 50 100 150
SPEED, km/h
SOO
T, m
g/m
3 DIESEL
B10COTTON
B20COTTON
B30COTTON
B40COTTON
B50COTTON
B100COTTON
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Conclusions The conversion of the pure cottonseed oil and of the
used cooking oil into bio-diesel produced fuel that at 40oc exhibited excellent properties, especially in the value of their viscosity that approached that of diesel. With the mixtures of these two bio-diesels with diesel as fuel, both cars ran smoothly, even at 100% bio-diesel.
The chassis measurements at full load showed a 10% increase in engine power when run with the mixtures of bio-diesel.
The fuel temperature change did not affect the power measurements. There was a small increase in the soot and NOx values when the fuel temperature increased.
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Conclusions With increasing bio-diesel content the soot values
dramatically decrease as compared to pure diesel as a fuel; the soot value was measured at 601 mg/m3 with diesel as a fuel as compared to 174,45 mg/m3 with B100 cottonseed bio-diesel.
The injection timing was changed from its factory value by 5o , delaying it and advancing it. There was an increase in soot and a decrease in the NOx values with advanced timing as compared to delayed timing.
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TEST RESULTSPM comparison
0
100
200
300
400
500
600
Volvo 27Kw at 1780 RPM Escort 15Kw at 1867RPM
Volvo 28Kw at 1900 RPM Escort 15,6Kw at 2091RPM
Volvo 41 Kw at 3430 RPM Escort 20,2Kw at2749 RPM
mg/m³
Escort Diesel Volvo Diesel Escort B10 cotton Volvo B10 Cotton Escort B20 cottonVolvo B20 cotton Escort B30 Cotton Volvo B30 cotton Escort B40 cotton Volvo B40 CottonEscort B50 Cotton Volvo B50 cotton Escort B100 Cotton Volvo B100 Cotton
PM comparison
0
50
100
150
200
250
Transit 26Kw at 1930 RPM Escort 15Kw at 1867RPM
Transit 27Kw at 2050 RPM Escort 15,6Kw at2091 RPM
Transit 28 Kw at 2730 RPM Escort 20,2Kw at2749 RPM
mg/m³
Escort Diesel Transit Diesel Escort B10 cotton Transit B10 Cotton Escort B30 Cotton Transit B30 cotton Escort B50 Cotton Transit B50 cottonEscort B100 Cotton Transit B100 Cotton
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TEST RESULTSNOX comparison
0
100
200
300
400
500
600
700
800
900
1000
Volvo 27Kw at 1780 RPM Escort 15Kw at 1867RPM
Volvo 28Kw at 1900 RPM Escort 15,6Kw at 2091RPM
Volvo 41 Kw at 3430 RPM Escort 20,2Kw at2749 RPM
PPM
Escort Diesel Volvo Diesel Escort B10 cotton Volvo B10 Cotton Escort B20 cottonVolvo B20 cotton Escort B30 Cotton Volvo B30 cotton Escort B40 cotton Volvo B40 CottonEscort B50 Cotton Volvo B50 cotton Escort B100 Cotton Volvo B100 Cotton
NOX comparison
0
100
200
300
400
500
600
700
800
Transit 26Kw at 1930 RPM Escort 15Kw at 1867RPM
Transit 27Kw at 2050 RPM Escort 15,6Kw at2091 RPM
Transit 28 Kw at 2730 RPM Escort 20,2Kw at2749 RPM
PPM
Escort Diesel Transit Diesel Escort B10 Cotton Transit B10 CottonEscort B30 Cotton Transit B30 Cotton Escort B50 Cotton Transit B50 CottonEscort B100 Cotton Transit B100 Cotton
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TEST RESULTSCO2 comparison
9,500
10,000
10,500
11,000
11,500
12,000
12,500
Volvo 27Kw at 1780 RPM Escort 15Kw at 1867RPM
Volvo 28Kw at 1900 RPM Escort 15,6Kw at2091 RPM
Volvo 41 Kw at 3430 RPM Escort 20,2Kw at2749 RPM
Vol%
Escort Diesel Volvo Diesel Escort B10 cotton Volvo B10 Cotton Escort B20 cottonVolvo B20 cotton Escort B30 Cotton Volvo B30 cotton Escort B40 cotton Volvo B40 CottonEscort B50 Cotton Volvo B50 cotton Escort B100 Cotton Volvo B100 Cotton
CO2 comparison
0,000
2,000
4,000
6,000
8,000
10,000
12,000
14,000
Transit 26Kw at 1930 RPM Escort 15Kw at 1867RPM
Transit 27Kw at 2050 RPM Escort 15,6Kw at2091 RPM
Transit 28 Kw at 2730 RPM Escort 20,2Kw at2749 RPM
Vol%
Escort Diesel Transit Diesel Escort B10 Cotton Transit B10 CottonEscort B30 Cotton Transit B30 Cotton Escort B50 Cotton Transit B50 CottonEscort B100 Cotton Transit B100 Cotton
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CONCLUSIONS PM emissions are consistently lower for all biodiesel
blends as compared to neat diesel. This decrease is more pronounced at lower power levels.
NOX emissions are consistently higher for all biodiesel blends as compared to neat diesel. This increase is more pronounced at higher power levels. NOX emissions increase in the Volvo and Ford Transit, but they do not vary appreciably in the Ford Escort.
CO2 emissions with all blends are consistently lower in the VOLVO engine, increase in the FORD ESCORT and do not vary appreciably in the FORD TRANSIT engine when compared to neat diesel, except at the fourth gear.
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DIRECT vs. INDIRECT With regards to lower NOX emissions in the Ford Escort
it should be noted that the combustion temperature in an IDI engine is lower than in a DI engine due to higher heat losses in the area of the prechamber, and therefore NOX emissions are reduced.
Other reasons for explaining the data differences are the presence of an ECU management system in the VOLVO, the EGR system for the recirculation of the exhaust gases in the VOLVO and FORD TRANSIT engines and the absence of an ECU or EGR system in the Greek FORD ESCORT.
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