Optimizing hydrogen knock limit in SI engines: Role of methanol blends and injection pressure

Hydrogen addition is a promising way to enhance the SI engine combustion, however the occurrence of combustion limit its practical use, especially at higher hydrogen share. This study focus on combining methanol blending and liquid fuel injection strategy to optimize the hydrogen knock limit. Methanol volume ratios of 20%, 35%, and 50%, along with injection pressures of 80, 110, and 140 bar, are considered. The outcome showed that methanol addition and higher injection pressures reduced the cylinder pressure, heat release rate and combustion temperature because of methanol charge cooling and wall or piston surface impingement at higher injection pressure. These effects mitigated the end-gas autoignition and allowed higher hydrogen flow rate. The hydrogen knock limit increased from 14 LPM at baseline case to 20 LPM for M50 blend at 140 bar injection pressure, corresponding to a 42.8% improvement. Although methanol blending and higher injection pressure lowered BTE and BMEP, hydrogen addition recovered the performance and combustion characteristics. Methanol blending and higher injection pressure reduced the CO 2 and NO x emissions and increased the CO emission, while hydrogen showed an opposite emission trend. The findings exhibits that methanol blending and injection pressure variation can be adopted as a calibration parameters to increase hydrogen substitution and mitigate the combustion knock.