Reduction of exhaust emissions was investigated in a modern diesel engine equipped with advanced diesel after treatment system using a Gas-to-Liquid (GTL) fuel, a cleaner burning alternative diesel fuel. This fuel has near zero sulfur and aromatics and high cetane number.
Some specially prepared GTL fuel samples were used to study the effects of GTL fuel distillation characteristics on exhaust emissions before engine modification. Test results indicated that distillation range of GTL fuels has a significant impact on engine out PM. High cetane number also improved HC and CO emissions, while these fuel properties have little effect on NOx emissions. From these results, it was found that low distillation range and high cetane number GTL fuel can provide a favorable potential in NOx/PM emissions trade-off. In order to improve the tail-pipe emissions in the latest diesel engine system, the engine modifications were carried out for the most favorable GTL fuel sample. The amount of EGR, the injection timing and exhaust port injection for catalyst were calibrated to reduce NOx while maintaining the fuel consumption. In the vehicle emission test, it was found that the optimizations of both the engine and GTL fuel enabled the potential to reduce NOx/PM emissions.
Furthermore, the engine hardware specifications, such as compression ratio and injection nozzle, were explored for the future diesel engine utilizing GTL fuels. The investigation results indicated that low compression ratio and high flow rate injection nozzle were beneficial in further reduction of emissions and improvement of engine output power.