Exploring methanol and CNG as low-reactivity fuels in reactivity controlled compression ignition for single-cylinder diesel engines: An experimental based comparative analysis at full load condition

The present study aimed to assess comprehensively the relative advantages and shortcomings of methanol and CNG in RCCI combustion mode operated on a conventional diesel engine under identical operating conditions. The study has investigated the characteristics of peak pressure, combustion stability, emissions, maximum energy share and overall reactivity of methanol and CNG operation under multiple injection strategy at 5 different energy share levels. It was observed that the deteriorated stability of combustion with increasing participating ratio limits the maximum share of methanol to be 59 %. However, the study indicates that methanol achieves significantly greater NOx reductions, whereas CNG offers improved combustion stability and soot control, underscoring the complementary trade-offs between the methanol and CNG RCCI applications. Compared to CNG counterpart, methanol RCCI operation exhibited 1.6 times lower NOx emissions, while CNG demonstrates 62 % improved combustion stability and 33.33 % reduced soot emissions. The methanol operation further exhibited higher BTE by 3.55 % and 42 % lower CO emissions, whereas CNG operation achieved relatively 57 % lower UHC emissions, identifying the conflicting characteristics of the operations. The study also revealed that advanced injection timing effectively reduces CO, UHC, and soot emissions, whereas retarded injection timing strategy proved to be more effective in lowering NOx emissions.