Effect of Olefin Content in Gasoline on Knock Characteristics and HCHO Emission in Lean Burn Spark Ignition Engine

In transportation sector, higher engine thermal efficiency is currently required to solve the energy crisis and environmental problems. In spark ignition (SI) engine, lean-burn strategy is the promising approach to improve thermal efficiency and lower emissions. Olefins are the attractive component for gasoline additives, because they are more reactive and have advantage in lean limit extension. However, owing to lower research octane number (RON), it is expected to exhibit the drawback to reducing the anti-knock performance. The experiments were performed using a single-cylinder engine for 6 fuel types including gasoline blends which have difference in RON varying between 90.4 and 100.2. The results showed that adding olefin content to the premium gasoline provided unfavorable effect on auto-ignition as the auto-ignition happened at unburned gas temperature of 808 K which was 52 K lower at excess air of 2.0. Thus, it reduced anti-knock performance. Additional oxygenated fuels such as ethanol and ETBE helped improve the anti-knock performance by 4.9% and 5.7% respectively. S5H+1-hexene fuel was found to be highest reactivity which would have high possibility of knocking. HCHO emission increased linearly with decreasing RON at lean burn condition which was expected to undergo low-temperature reaction processes.