Characterization of Diesel Engine Generator Operating at Different

Compression Ratio Fuelled with Palm Oil Biodiesel

Belyamin Belyamin1,a, Alias Mohd. Noor2,b, Mohanad Hamzah Hussein3,c, and Mazlan Said4,d

1 Transportation Research Alliance, Universiti Teknologi Malaysia, 81300 UTM Skudai,

Johor, Malaysia 2 Mechanical Engineering Department, Politeknik Negeri Jakarta, Depok 16425, Indonesia

3Mechanical Engineering Faculty, Universiti Teknologi Malaysia, 81300 UTM Skudai,

Johor, Malaysia

a belyamin@utm.my,

a belyamin@yahoo.com,

balias@fkm.mail.utm.my,

cmohanadhamazah@yahoo.com ,

d mazlan-s@utm.my

Keywords: Palm oil methyl ester, variable compression ratio, four stroke, direct injection

Abstract. Experiment to determine exhaust gas emission and combustion characteristics of a

compression ignition generator was carried out. The experiment used single cylinder four strokes

direct injection engine which was fuelled with diesel and palm oil methyl ester of B2 (blends 2%

palm oil methyl ester with 98% diesel on a volume basis), B5, B7 and B10. The experiment was

conducted at a fixed engine speed of 3000 rpm and 50% load with variety compression ratios of

16:1, 18:1, and 20:1and 22:1. Optimum compression ratio, influence of compression ratio on

specific fuel consumption and thermal efficiency were examined. Palm oil methyl ester produce

better output when the engine operate with variable compression ratio. Specific fuel consumption

decrease, NOx increase and thermal efficiency increase when optimum compression ratio of engine

is operated.

Introduction

There is a global increase in the investigation on the application of alternative fuel sources for

daily use, such as biodiesel and alcohol. This is due to the fact that petroleum products are

becoming very scarce and expensive and also the price of petroleum products is always on the high

side. There is also an awareness of air pollution caused by the extensive use of conventional fuel in

an internal-combustion engine.

In the past two decades, vegetable oil such as mahua oil, sun flower, seed oil, waste cooking oil,

and palm oil have been used as a substitute to diesel in an internal-combustion engine [1, 2, 3].

These papers study the performance and emission characteristic of generator fueled with biodiesel

or its blend. It shows that biodiesel can substitute fossil fuel in an internal-combustion engine with

or without engine modification. It is also economical and competitive compare to pure diesel. When

the fuel is waste palm oil, no engine modification is required.

In addition, biodiesel has lower sulphur, aromatics contents, and net carbon dioxide (CO2)

emission [4]. It has better lubricity and biodegradability and less toxic relative to fossil diesel [5].

Bio diesel can be used readily since it can be mixed at any proportion with diesel. This enables it to

be applied immediately in diesel power generator without much modification. Considering exhaust

emissions, the use of bio diesel results in lower emissions of unburnt hydrocarbons, carbon

monoxide, smoke and particulate matter beside some increase in emissions of NOx [6]. A number of

researchers have investigated vegetable oil-based fuels [2, 3, 7, and 8]. Vegetable oil can be safely

burnt for a short period of time in a diesel engine [3]. However, the use of raw vegetable oil for

extended period of time may result in severe engine deposits, piston ring sticking, injectors choking,

and thickening of the lubricating oil.

This experiment is to determine exhaust gas emission and combustion characteristics of a

compression ignition generator using B2, B5, B7 and B10.

Applied Mechanics and Materials Vol. 388 (2013) pp 241-245Online available since 2013/Aug/30 at www.scientific.net© (2013) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMM.388.241

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Methodology

Experiment to examine combustion characteristic and exhaust gas emission was conducted on a

four stroke single-cylinder diesel engine generator for variety CR (Compression ratio) and fuel such

as diesel fuel, D, and biodiesel formulation, B2, B5, B7 and B10.

Diesel fuel was combusted in diesel generator Yanmar l70N6-MTRIYJ of standard compresion

ratio 20. Power generated was loaded by set of lamps. Electric current and voltage of the lamps were

measured to determine power. This method is an alternative way to determine power by measuring

electrical power instead of mechanical power. In mechanical power, the power is observed by

torque measurement. Besides, fuel consumed was measured by determining time taken by diesel

generator to consume certain amount of fuel. The rotation of the engine was also monitored. The

exhaust gases emissions such as NOx, CO, CO2 and exhaust smoke density was measured by using

the emission analyzer. After combustion of pure Diesel fuel, The experiment was repeated using

fuel of biodiesel formulation of 2% biodiesel and 97% diesel (B2), B5, B7, and B10.

The experiments were repeated for different compression ratio. Variety of CR is achieved by

changing the cylinder head gasket thickness. CR increase when gasket thickness is reduced.

All these results were discussed to determine the effect of changing the CR and fuel formulation.

Result and Discussion

Specific Fuel Consumption. Fuel consumption, FC, is calculated by Equation 1.

FC = V / t. (1)

Specific Fuel Consumption is then calculated by Equation 2

SFC = FC/ P. (2)

The variation of Specific Fuel Consumption (SFC) with Compression Ratio (CR) is given in Fig. 1.

It can be observed that the SFC is a clear indication of efficiency with which the engine develops

power. The smaller SFC indicates the more effective use of fuel to generate power. For all fuels

tested, the SFC have optimum value at CR 20. This is due to increase of temperature in combustion

chamber, leading to complete combustion. It has been observed that the maximum SFC of B2

reduced by 0.96% at CR 20 relative to CR 22. At CR 18 and 16, SFC B5 and B7 have the highest

rise of SFC by 1.1%, 1.26% respectively. This indicates the CR 18 and 16 is not a proper

compression ratio to be used. This is because to be efficient in use of fuel is to use fuel in condition

with lower SFC. This happen in CR 20 to 22. B10 always have the higher value of SFC which mean

the worst one in term of fuel efficiency. At higher percentage of blends, the SFC increases due to

decrease in calorific value.

Thermal Efficiency. Thermal efficiency is calculated by Equation 3

�th = P/ Qin. (3)

Qin is calculated by Equation 4

Qin = m CV . (4)

The thermal efficiency (ɳth) of the engine is considered one of the most important criteria for

evaluating the performance of the engine. It indicates the combustion effectiveness of the engine.

242 Advances in Thermofluids

The �th is defined as the actual work per cycle divided by fuel chemical energy (fuel calorific

value). Fig. 2 shows the variation in �th with CR for blends fuel tested. The �th of biodiesel at all

blends was found to be lower than diesel for all CR monitored. This might be due to lower fuel heat

value and so higher fuel consumption of the bio diesel blends to produce the same power.

In this figure, it appears that the optimum �th of B2 occur at CR 20. This may be due to the fuel

calorific value and low SFC. At CR 18 and CR 16 the �th of B5, B7 reduce by 11%, 17%

respectively compare to CR 20, it was also observed that �th of biodiesel can follow the increase of

�th of biodiesel although the value is lower than that of diesel. Due to their low volatility and high

viscosity, biodiesel perform relatively better at higher compression ratios [9].

Exhaust Gas Emission

Nitrogen Oxide. The variation of Nitrogen Oxide (NOx) with respect to CR for different blends

and constant load is shown in Fig. 3. NOx emission for diesel and other blends increase when the

CR is increased. The augmentation in the biodiesel ratio in the fuel blend increased NOx emissions

by 1.07%, 1.12%, 1.16% and 1.18% for B2, B5, B7 and B10, respectively, the reason for higher

NOx emission for blends is higher peak temperatures. This figure shows an increase in NOx by 1.3%

at CR 22 while the NOx decreased by 17.7% and 30% at CR 18:1 and 16:1 respectively as compared

to the CR 20. The changes in NOx resemble up to some extent to exhaust temperature which is

related to an increase in CR.

Carbon Monoxide. Fig. 4 illustrate the variation of CO for variety fuel blends with respect to

CR. From this figure it seen that the specified blends produce less CO emission than diesel for every

CR at applied load, it might due to increase the cylinder temperature. Therefore engine temperature

Fig. 1. Variation of specific fuel consumption

with compression ratio for different fuel blends

Fig. 2. Variation of thermal efficiency with

compression ratio for different fuel blends

Fig. 3. Variation of Nitrogen Oxide with

compression ratio for different fuel blends

Fig. 4. Variation of Carbon Monoxide with

compression ratio for different fuel blends

Applied Mechanics and Materials Vol. 388 243

lead to better combustion process and might cause less CO emission. The CO decrease by 29.1%,

10.87%, 4.2% and 0.5% when the compression ratio increase from 20 to 22 for diesel,B2,B5,B7

and B10 respectively, This could be because biodiesel provide more oxygen to the combustion

chamber. This lead to the more complete combustion. The other reason is that the percentage of CO

decreases due to rising temperature in the combustion chamber. physical and chemical properties of

the fuel, air–fuel ratio, the effects of fuel viscosity on spray quality will be expected to cause CO

emission increase with vegetable oil fuels [10].

Carbon Dioxide. The variation of CO2 with CR is shown in Fig. 5. From this figure, it can be

observed that the CO2 emission when enhine operating with CR 22 increases by around 18% than

CR20. In decreasing CR, blends of fuel increase its CO2 emission by 4%, 4.5%, 8% and 11% for the

B2, B5, B7 and B10 respectively. This is due to the high oxygen content of blends. Higher amounts

of CO2 is an indication of complete combustion of fuel in the combustion chamber. It also relates to

the exhaust gas temperature. CO2 emissions of the fuel blends slightly increase by increasing the

load for specified compression ratios due to complete combustion.

Smoke Density. The variation of Smoke density emission with VCR at constant load is shown in

Fig. 6. In this figure, it was shown that the smoke density increased by 35% and 60% when the CR

decreased to 18 and 16 respectively. At lower CR the temperature is lower. Incomplete combustion

in the combustion chamber then lead to more smoke exhausted from the engine. The smoke

decreased when the blends percentage is increased. These figures show that the smoke was reduced

significantly by around 9%, 12%, 17% and 22% for B2, B5, B7 and B10 than diesel. In addition, it

was found that the maximum reductions were around 20% at CR 22 for all fuel blends than CR20,

this is due to the increase of inside temperature of the combustion chamber and because palm oil

contains more oxygen which improves the combustion process. At the end this will decrease the

smoke. The Smoke is emitted from diesel engines because of the incomplete combustion in the

combustion chamber.

Conclusion

An experimental was conducted on direct injection diesel engine generator evaluate the

performance, combustion and exhaust emission at different blends and compression ratio. Bio diesel

blend can replace pure diesel oil although its heating value is relative lower. Biodiesel replacement

to pure diesel reduce CO emission and increase CO2. It indicates better combustion performance.

Optimum CR to provide optimum SFC and Thermal efficiency is 20 and above

Fig. 5. Variation of Carbon Oxide with

compression ratio for different fuel blends

Fig. 6. Variation of Smoke density with

compression ratio for different fuel blends

244 Advances in Thermofluids

Acknowledgment

The authors are grateful to the Ministry of Higher Education and Universiti Teknologi Malaysia for

grant GUP project under Vot Q.J130000.2609.00J35 and Q.J130000.2444.00G54.

Nomenclature

B2 blend of 2% biodiesel and 98% diesel

B5 blend of 5% biodiesel and 95% diesel

B7 blend of 7% biodiesel and 93% diesel

B10 blend of 10% biodiesel and 90% diesel

CO carbon monoxide

CO2 carbon dioxide

CR compression ratio

CV Calorific Value of fuel

D 100% diesel

FC Fuel consumption

m mass flow rate of fuel

NOx nitrogen oxides

O2 oxygen

P Power generated

Qin Heat input

t time taken to consume the fuel

SBFC specific brake fuel consumption

VCR variable compression ratio

V volume of fuel used

ɳth brake thermal efficiency

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Applied Mechanics and Materials Vol. 388 245

Advances in Thermofluids 10.4028/www.scientific.net/AMM.388 Characterization of Diesel Engine Generator Operating at Different Compression Ratio Fuelled with

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