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

Abstract

Abstract. This study experimentally investigates the effects of ignition timing on combustion behavior, knock propensity, 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 tests were conducted at 3000, 4000, and 5000 rpm with a ± 5 °CA variation in spark timing. Ignition timing was identified as the dominant parameter governing combustion phasing; advancing the spark timing shifted peak cylinder pressure closer to top dead center, increasing knock propensity by approximately 30%. Cycle-resolved analysis at 4000 rpm under advanced ignition revealed that G100 reached a maximum Knock Peak Value of 6.26 bar in a single cycle, indicating intermittent heavy knock. In contrast, retarded spark timing shifted combustion toward the expansion stroke, reducing peak pressure, indicated mean effective pressure (IMEP), and knock intensity, thereby maintaining all fuels within the knock-limited regime. G100 exhibited strong sensitivity to spark timing, whereas alcohol–gasoline blends produced steeper pressure gradients at medium and high engine speeds. In particular, at high engine speeds, E30 demonstrated a more controlled heat release and improved combustion stability. Although cycle-averaged knock intensities were similar, G100 displayed higher peak knock sensitivity. Retarding the ignition timing effectively reduced NO and CO2 emissions by up to 14.2% and 16.6%, respectively, across all tested engine speeds. Additionally, the oxygenated structure of alcohol blends significantly suppressed soot emissions compared to gasoline, regardless of ignition timing and engine speed. Overall, combining E30 or ISB30 with moderated spark timing provides an effective strategy for controlling knock and reducing emissions under full-load conditions.