Modeling of a Methanol Fueled Direct-Injection Spark-Ignition Engine with Reformed-Exhaust Gas Recirculation

Methanol is a promising fuel for future spark-ignition engines. Its properties enable increased engine efficiency. Moreover, the ease with which methanol can be reformed, using waste exhaust heat, potentially offers a pathway to even higher efficiencies. The primary objective of this study was to build and validate a model for a methanol fueled direct-injection spark-ignition engine with on-board fuel reforming for future investigation and optimization. The second objective was to understand the combustion characteristics, energy losses and engine efficiency. The base engine model was developed and calibrated before adding a reformed-exhaust gas recirculation system (R-EGR). A newly developed laminar burning velocity correlation with universal dilution term was implemented into the model to predict the laminar burning velocity with the presence of hydrogen in the reforming products. At the same EGR ratio, there is a small increase in the engine efficiency with fuel reforming compared to conventional EGR. This is mainly due to the reduction of pumping work. For the R-EGR cases, around 60% of the increase in the brake efficiency is due to the reduction of pumping work. Although the increase in brake efficiency is very small, the maximum brake thermal efficiency for the R-EGR cases is higher than for the conventional EGR cases due to a significant increase in the dilution limit. With R-EGR dilution, the maximum brake thermal efficiency was found to increase by 6.9% relative to the baseline case.