Characterisation of ignition delay period for a compression ignition engine operating on blended mixtures of diesel and gasoline

The widely different autoignition characteristics of diesel and gasoline has been exploited in blends of varying proportion here to investigate the influence on ignition delay (ID) and in turn, charge preparation, heat release and injection timing requirements for the best combustion phasing in a compression ignition engine. Experimental studies have been carried out on a light-duty turbocharged direct-injection diesel engine with pump injection system to test diesel–gasoline fuel blends comprising up to 80%vol. gasoline. ID increases with the gasoline content of the blend, and generally gives rise to an increase in the premixed heat release. The duration of combustion is not markedly changed. Higher gasoline blends retarded the start of fuel injection by up to 3° crank angle (CA) due to changes in physical properties. The change in injection timing affected combustion phasing but not ID directly. The contribution of chemical delay to ID has been investigated using CHEMKIN. The increases in ID period and premixed combustion heat-release rate associated with higher gasoline blend fractions are found to be caused by the chemical delay. Physical delay is less dependent on blend proportions and more dependent on engine operating condition, which increases with higher engine speed and intake boost pressure.