Combustion characteristics of methanol engine applying TJI-HPDI with optimized pre-chamber nozzle structure under different injection and spark strategy

Methanol fuel faces challenges in achieving mixing controlled combustion (MCC) due to its low cetane number. This study proposes utilizing turbulent jet ignition to facilitate methanol MCC under high-pressure direct injection mode, namely TJI-HPDI. Three coordination schemes were developed numerically based on the projection angles between hot jets and main methanol spray plumes axis: opposing (Base design), opposing staggered (Design 1), and circumferential staggered interference (Design 2). Varied orifice diameters was employed to regulate jet energy and velocity. The results indicated that Design 2-BSB (Big-Small-Big orifice) scheme exhibited superior combustion and emission performance. Furthermore, the impact of start of main injection timing (SOI) on ignition and combustion characteristics was investigated under this scheme. An SOI of −12 °CA after top dead center (TDC), creating a 7 °CA interval between spark and SOI timing, achieved optimal ITE by minimizing the duration of CA10-CA50 and optimization methanol mixture distribution around hot jets. Additionally, pre-chamber (PC) spark ignition timing (ST) effects were also explored, with the optimal timing at −8 °CA ATDC. ST has minimal impact on heat release rate (HRR), because high-energy jets could ensure rapid and stable combustion. Moreover, the combustion stability of TJI-HPDI was demonstrated, underscoring the importance in understanding and optimizing TJI-HPDI ignition processes.