There is a growing consensus that there will not be a single alternative to fossil fuels, but rather different fuels, fuel feedstocks, engine types and operating strategies. For stationary diesel engines, straight vegetable oils are an interesting alternative to fossil diesel, because of their potential for lower life cycle greenhouse gas emissions. Using animal fats is also compelling, as it does not imply the cultivation of oil-bearing seeds and related emissions, not to mention the ‘food versus fuel’ debate.
The aim of the present work is to correlate engine performance and durability with the properties (composition) of these alternative fuels, to provide a basis from which standards can be formulated for the properties of oils and fats to be used as engine fuel.
Tests on different oils and fats are reported. Rapeseed oil, palm oil and animal fat were analyzed for their physical and chemical properties (viscosity, composition, unsaturation, degradation parameters) and were used in a turbocharged truck diesel engine. Tests were done at a range of engine speeds and torque settings and in-cylinder pressure, emissions and specific fuel consumption were determined. The engine performance on the different fuels is compared to diesel fuel and related to the properties of the oils and fats.
Concerning emissions, NOx emissions were found to decrease, consistent with the lower rate of heat release. This, combined with higher HC emissions, can probably be explained through less effective atomization due to the higher viscosity of the oils and fat, even though a preheating temperature of 70°C was used. On the other hand, soot emissions were found to decrease.