A Comparative Study on the Effects of Ignition Timing on Combustion, Knock and Emissions in an Alcohol-Gasoline Fueled DISI Engine

This study experimentally investigates the influence of ignition timing on combustion characteristics, knock behavior, and emissions in a direct-injection spark-ignition (DISI) engine fueled with gasoline (G100) and 30 vol.% alcohol–gasoline blends (E30 and ISB30). Full-load experiments were conducted at 3000, 4000, and 5000 rpm with ±5°CA spark timing variations. Ignition timing was identified as the dominant parameter controlling combustion phasing and knock intensity. Spark advancement shifted peak cylinder pressure toward top dead center, increased the maximum pressure rise rate (Rmax), and intensified knock tendency. Under advanced ignition at 4000 rpm with G100, the knock peak value (KPV) reached 6.26 bar, indicating severe knock conditions. In contrast, spark retard shifted combustion toward the expansion stroke, reducing peak pressure and IMEP while significantly lowering knock intensity and maintaining stable operation. Fuel-dependent sensitivities were observed: G100 exhibited higher knock susceptibility under advanced timing, whereas ISB30 produced steeper pressure gradients at elevated speeds. E30 demonstrated smoother heat release development and improved combustion stability. Retarded ignition timing reduced NO and CO2 emissions for all fuels. Soot formation was primarily governed by fuel oxygen content, with alcohol blends substantially suppressing soot compared to gasoline, independent of ignition timing. Overall, the results indicate that combining high-alcohol blends with moderated ignition timing provides an effective strategy for mitigating knock and reducing emissions under full-load DISI engine operation.