The impact of ignition delay and further fuel properties on combustion and emissions in a compression ignition engine

Better understanding of combustion and formation of exhaust gas pollutants of fuels is needed in order to meet stringent regulation standards of a diesel engine. The cetane number is one of the most-cited indicators of diesel fuel quality. This paper presents experimental studies with a wide range of fuels to investigate the effect of cetane number on combustion and exhaust emissions (CO, NOx, PM, particle number size distribution). The fuel ignitability was controlled in two different ways: naturally, by using seven fuels (Dearomatised Hydrotreated Stream, Hydrotreated Non-Dearomatised Stream, Soy Methyl Ester, Rapeseed Methyl Ester, Heavy Paraffinic Stream, C10-C14 Paraffins, and C14-C17 Paraffins) with different cetane numbers, and through the use of an ignition improver blended into a single base fuel (Hydrotreated Non-Dearomatised Stream (NDH)) to change the ignition chemistry of the fuel while keeping physical properties unchanged. The tests were performed in naturally-aspirated single-cylinder DI diesel engine at 1200 rpm and 600 bar injection pressure at 4 bar and 6 bar IMEP. The engine tests were carried out at constant fuel injection timing and constant start of combustion timing. A strong positive correlation was found between ignition delay and CO emissions. The effect of physical and chemical properties of the fuel on NOx and particulate emissions became more dominant at higher load. Overall the results showed that changes in the fuel physical properties and molecular structure, in particular, the incorporation of oxygen, impacted on combustion and emissions through various routes in addition to the effects of ignition delay only.