Potential of Synthetic Fuels in Future Combustion Systems for HSDI Diesel Engines 2006-01-0232

In view of limited crude oil resources, alternative fuels for internal combustion engines are currently being intensively researched. Synthetic fuels from natural gas offer a promising interim option before the development of CO₂-neutral fuels. Up to a certain degree, these fuels can be tailored to the demands of modern engines, thus allowing a concurrent optimization of both the engine and the fuel.

This paper summarizes investigations of a Gas-To-Liquid (GTL) diesel fuel in a modern, post-EURO 4 compliant diesel engine. The focus of the investigations was on power output, emissions performance and fuel economy, as well as acoustic performance, in comparison to a commercial EU diesel fuel. The engine investigations were accompanied by injection laboratory studies in order to assist in the performance analyses.

The research effort revealed that GTL diesel fuel operation provided significant advantages with regard to the PM/NO_X emissions trade-off, when compared with the EU diesel, for a given hardware configuration and under identical operating conditions. This was found to be particularly the case at low and medium engine loads. HC and CO emissions for lowest NO_X emission levels were also improved while maintaining a favorable fuel consumption level and ensuring a robust and stable combustion process. Furthermore, it was demonstrated that for the chosen test engine, a pilot injection at full load at 2000 rpm has a positive effect. Scope exists for additional improvements through optimized engine software calibration (charge cooling, EGR, boosting) and an optimized hardware specification. The analysis of the hydraulic investigations revealed that the chemical composition of the fuel is the major factor influencing the emissions, rather than any difference in the hydraulic performance of the injection system.