Exploring energy utilization of the methanol/dimethyl ether dual-fuel engine under the methanol reforming strategy: A comparison of different low-temperature combustion modes

Numerous studies have explored methanol and dimethyl ether (DME) as alternative engine fuels to enhance thermal efficiency and lower emissions. In this study, based on methanol reforming, a new potential strategy for the realization of the methanol/DME dual-fuel compression-ignition engine by fueling only methanol is proposed. The methanol/DME dual-fuel engine under three low-temperature combustion modes (i.e., reactivity controlled compression ignition (RCCI), reverse-reactivity controlled compression ignition (R-RCCI), and homogenous charged compression ignition (HCCI)) is computationally optimized, and the methanol reforming ratio is considered. The results demonstrate that the R-RCCI mode displays enhanced performance in both combustion efficiency and emissions, achieving an equivalent indicated specific fuel consumption (EISFC) of 152.3 g/kWh and nitrogen oxide (NOx) emissions far below the Euro VI regulatory threshold. A double injection of methanol with a minor secondary injection in the R-RCCI mode facilitates more pronounced stratified combustion, and the ringing intensity (RI) can be well controlled. The mode-specific optimal DME energy ratio was determined, approximately 40 % for RCCI and R-RCCI, and around 14 % for HCCI. The demand for the DME energy ratio can be realized by the onboard methanol reforming system, which demonstrates the feasibility of the combination of the fuel reforming strategy with low-temperature combustion modes.