The effects of increasing FAME biodiesel content on combustion characteristics and HC emissions in high-EGR low temperature combustion

An experimental study was performed on a single-cylinder high-speed direct-injection diesel research engine to determine the effects of increasing biodiesel content on the combustion characteristics and HC emissions during high-EGR low temperature combustion operation. Two test points, a moderately dilute low-load condition and a high-EGR medium-load condition, were examined at a constant speed of 1500 rpm with a fixed input fuel energy content and start of injection timing. The results show the two operating conditions to have very different sensitivities to the fuel’s biodiesel content and, as a result, to demonstrate contrasting behaviour with respect to the variation of HC emissions with blend composition. For the low load, medium dilution case, ignition delay, combustion phasing and combustion duration are essentially independent of biofuel content while HC emissions are reduced with respect to the base diesel. For the high-EGR, medium load condition, ignition delay is reduced and combustion phasing advances with increasing levels of biofuel content. HC emissions increase with increasing biofuel content. Crank-angle aligned HC measurements indicate the significance of the piston/wall crevice volume as an HC source in high-EGR LTC.