Combination of Combustion Concept and Fuel Property for Ultra-Clean DI Diesel

Experimental investigations were previously conducted with a direct-injection diesel engine with the aim of reducing exhaust emissions, especially nitrogen oxides (NOx) and particulate matter (PM). As a result of that work, a combustion concept, called Modulated Kinetics (MK) combustion, was developed that reduces NOx and smoke simultaneously through low-temperature combustion and premixed combustion to achieve a cleaner diesel engine. In subsequent work, it was found that applying a low compression ratio was effective in expanding the MK combustion region on the high-load side. The MK concept was then combined with an exhaust after-treatment system and applied to a test vehicle. The results indicated the attainment of ULEV emission levels, albeit in laboratory evaluations.

In the present work, the combination of the MK combustion concept and certain fuel properties has been experimentally investigated with the aim of reducing exhaust emissions further. The results indicated that the use of a high cetane number gas-to-liquid (GTL) fuel with a lower compression ratio provides a sufficiently long ignition delay to accomplish MK combustion. The effect on a simultaneous reduction of NOx and smoke was confirmed. The results also indicated that the use of GTL fuel can reduce the total hydrocarbon level substantially under a cold condition because of its good ignition characteristics, with a high cetane number and high levels of paraffin compounds. As a result, one possible approach to the attainment of SULEV emission levels was found.