Low compression ratio diesel engines fueled with biodiesel by using spark-induced compression ignition

The objective of this study is to demonstrate a novel combustion system in which auto-ignition is induced by spark discharge into a pre-mixture formed during a long ignition delay time at a direct injection(DI) diesel engine with a low compression ratio. An experiment is conducted to investigate the potential of spark discharge on the auto-ignition process by changing the spark timing, injection timing, equivalence ratio, and fuel amount. The fuel used is lauric methyl ester, which is a fatty acid methyl ester that has relatively higher volatility and higher ignition quality than petro diesel fuel. The results obtained by single cylinder common-rail DI diesel engine show that with a volumetric efficiency of 34%, spark-induced compression ignition (SICI) combustion is observed. In this study, the auto-ignition timing is advanced by spark discharge and is controlled by the spark timing within 5 deg. CA. We also observed SICI combustion flame by constant volume combustion vessel using direct flame high-speed photography and OH radical chemiluminescence spectroscopy by means of the combination of an optical band-pass filter, an image intensifier and CCD camera. As a result, it was found that SICI occurs not by flame propagation due to spark ignition but by auto-ignition of pre-mixture formed by spray. It was also clear that the auto-ignition is induced by transportation of OH radical at spark plug with spray flow.