受爆震限制,氢气发动机的压缩比普遍低于柴油发动机,因此克服高压缩比下爆震燃烧限制对氢气发动机的应用具有重要意义。本研究通过数值模拟,研究了高压缩比条件下喷射策略结合点火时刻对缸内直喷氢气发动机爆震的抑制潜力。结果表明:压缩比为15时,随着喷射压力的增大,爆震强度(KI)先减小后增大;喷射压力为6 MPa时,KI最小,此时火花塞附近氢气分布更为富集,混合气较易点燃,火焰核心更为稳定;爆震强度随着喷射正时的变化呈非线性,当喷射正时为-100°时,缸内混合气分布更均匀,燃烧重心(CA50)更接近上止点,KI降到最低;仅通过调整喷射压力或喷射正时,最低KI值均未能降至1 MPa以下,需要延迟点火提前角以降低KI值。
Due to the knock limitations, the compression ratio of hydrogen engines is generally lower than that of diesel engines. Overcoming the knock combustion constraints under high compression ratios is hence essential for the application of hydrogen engines. The numerical simulation was employed to investigate the potential of injection strategies combined with ignition timing to suppress knock in a direct-injection hydrogen engine under high compression ratio conditions.The results indicate that the knock intensity (KI) first decreases and then increases with rising injection pressure at a compression ratio of 15. The minimum KI occurs at an injection pressure of 6 MPa, where hydrogen distribution near the spark plug becomes more concentrated, promoting easier mixture ignition and the mixture forming a more stable flame kernel. The variation of knock intensity with injection timing is nonlinear. At -100°ATDC, the in-cylinder mixture distribution becomes more homogeneous, the combustion phasing (CA50) moves closer to top dead center (TDC), and KI reaches its lowest value. However, the lowest achievable KI values obtained by adjusting either injection pressure or injection timing alone still exceed 1 MPa. Therefore, delaying the ignition advance timing is necessary to further mitigate knock.