Combustion Characteristics of Biological Fuel in Diesel Engine

This paper presents the results of an experimental work carried out to evaluate the combustion and emission characteristics of ordinary coconut oil (COIL) blended fuel on unmodified indirect injection (IDI) diesel engine. Diesel fuel (DF2) was used for comparison purposes. The test results on coconut oil blended fuel showed that the addition of up to 30% coconut oil with DF2 has significantly increased brake power and net heat release rate with a net reduction in exhaust emissions such as HC, NOx, CO, smoke and poly-cyclic aromatic hydrocarbons (PAH). This means that COIL blended fuel has similar ignition quality as DF2, and indeed better combustion. However, COIL blended fuel increases specific fuel consumption due to higher specific density of coconut oil. When more than 30% of coconut oil is added (40% - 50%), the brake power produced and the net heat release rate are slightly less due to low internal energy, but better combustion still takes place. The carbon deposits on the injector were similar to those observed when the engine was running on diesel fuel. The engine did not have any initial starting and combustion noise problems when functioning on COIL blended fuels at an operating temperature of about 25 °C. These experiments have contributed to technical validation of the future use of coconut oil blended fuel in Malaysia, where the ambient temperature is between 23 °C to 33 °C. This program has given optimistic information to pave the direction for further research on coconut oil based fuel for diesel engine.