Simulation Study of Super Knock in Turbocharged Direct Injection Engine with Ethanol-Gasoline Blends

The process of low-speed pre-ignition(LSPI)caused by the oil droplets suspending in the combustion chamber was simulated by the method of injecting a certain amount of oil droplets directly into the chamber at the top dead center of compression stroke. After verifying the feasibility of calculation models and methods, the processes of LSPI and super knock induced by oil droplets were simulated numerically with different operating conditions and different ethanol blending rates(volume fraction)of ethanol-gasoline blends in a downsized turbocharged direct injection(DI)engine. The results demonstrate that super knock occurs in the engine cylinder with 10% or 20% ethanol(E10, E20)blending rates fuels. When ethanol blending rates is up to 30%(E30), although the LSPI phenomenon occurs and subsequently leads to a regular knocking combustion, the pressure rise amplitude is obviously reduced and the super knock does not appear. With speed up to 1 600 r/min, LSPI but no any knock occurs in engine cylinder. As blending rates are higher than 50%(E50), no LSPI happens in the cylinder under different operating conditions. There must be a LSPI phenomenon before super knock happens in the downsized turbocharged DI engine with ethanol-gasoline blends, but the LSPI phenomenon does not necessarily lead to a super knock process. © 2020, Editorial Office of the Transaction of CSICE. All right reserved.