Effects of Fuel Injection Method on Energy Efficiency and Emissions of SI Engine Fed with a Hydrogen-Rich Reformate
Various potential alternative fuels for internal combustion engines are studied nowadays to reduce dependency on fossil fuel. Hydrogen-rich reformate produced onboard as a result of fuel reforming in an internal combustion engine with a high-pressure thermochemical recuperation is a promising alternative gaseous fuel. This paper reports on the effects of the reformate fuel injection method on energy efficiency and combustion characteristics of a single-cylinder spark ignition (SI) engine with a high compression ratio (16:1) at steady-state conditions. A comparison between port (PFI) and direct (DI) reformate injection is performed. Engine performance and combustion parameters are evaluated and analyzed. For both injection strategies, a similar relatively high indicated efficiency (50%) is observed. This is a joint result of waste heat recovery and hydrogen combustion benefits. With the PFI method, the lower engine volumetric efficiency, due to hydrogen induction into the intake manifold, results in maximal power output limitation and to abnormal combustion. Contrary, DI strategy enables achieving maximal engine power. The heat release rate with the reformate DI is significantly higher compared to PFI for the same excess air ratio. The higher in-cylinder turbulence and stratification induced by direct injection process compared to the premixed charge PFI counterpart, resulting in a faster fuel burning. The available exhaust enthalpy of the PFI method is not sufficient to sustain the complete methanol conversion in the endothermic steam reforming reaction. An advanced spark timing and the lower engine compression ratio can be applied to increase the available exhaust enthalpy. A direct-injection of hydrogen-rich reformate shows a high potential of further efficiency improvement; though additional research on reformate injection strategy, engine compression ratio, and combustion processes optimization is essential.