Effects of GTL fuel properties on DI diesel combustion

Reduction of vehicle exhaust emissions is an important contributor to improved air quality. At the same time demand is growing for new transportation fuels that can enhance security and diversity of energy supply. Gas to Liquids (GTL) Fuel has generated much interest from governments and automotive manufacturers. It is a liquid fuel derived from natural gas, and its properties - sulphur free, low polyaromatics and high cetane number - make it desirable for future clean light-duty diesel engines. In this paper, the effects of distillation characteristics and cetane number of experimental GTL test fuels on direct injection (Dl) diesel combustion and exhaust emissions were investigated, together with their spray behaviour and mixing characteristics. The test results show that the lower distillation test fuels produce the largest reductions in smoke and PM emissions even at high cetane numbers. This is linked to the enhanced air/fuel mixing of the lighter fuel in a shorter time. The high ignitability and short ignition delay resulting from the high cetane number of all the GTL samples proved effective for reduction of unburnt emissions and combustion noise. Some experimental results are also presented when a modern high speed Dl diesel passenger car is run on neat GTL fuel and conventional diesel fuel. As the test results show, some benefits of GTL have been confirmed in exhaust emissions.