Dual-fuel diesel engine combustion with hydrogen, gasoline and ethanol as fumigants: Effect of diesel injection timing

Premixed compression ignition (CI) combustion has attracted increasing research effort recently due to its potential to achieve both high thermal efficiency and low emissions. Dual-fuel strategies for enabling premixed CI have been a focus using a low reactivity fumigant and direct diesel injection to control ignition. Alternative fuels like hydrogen and ethanol have been used as fumigants in the past but typically with diesel injection systems that did not allow the same degree of control or mixing enabled by modern common rail systems. In this work we experimentally investigated hydrogen, ethanol and gasoline as fumigants and examined three levels of fumigant energy fraction (FEF) using gasoline over a large direct diesel injection timing range with a single cylinder diesel engine. It was found that the operable diesel injection timing range at constant FEF was dependent on the fumigant's propensity for autoignition. Peak indicated gross cycle efficiency occurred with advanced diesel injection timing and aligned well with combustion phasing near TDC as we found in an earlier work. The use of hydrogen as a fumigant resulted in very low HC emissions compared with ethanol and gasoline, establishing that they mainly result from incomplete combustion of the fumigated fuel. Hydrogen emissions were independent of diesel injection timing and HC emissions were strongly linked to combustion phasing, giving further indication that squish and crevice flows are responsible for partially burned species from fumigation combustion.