Super-knock suppression for highly turbocharged spark ignition engines using the fuel of propane or methanol

Abstract

Super-knock is the main obstacle to improve power density and fuel efficiency of highly boosted gasoline engines. Previous investigations show that pre-ignition and detonation are the two key combustion processes of super-knock. The former is the inducement and the latter is the root reason of how super-knock could damage engines dramatically. Lots of studies have been conducted for suppressing super-knock through eliminating pre-ignition. Using a rapid compression machine, this study explores the stoichiometric propane or methanol mixture to suppress super-knock by eliminating detonation. Under the same pressure at the end of compression, the same fuel energy density and the same charged fresh air, the peak pressure of propane mixture could be reduced dramatically and the pressure oscillation could be eliminated, when compared to iso-octane mixture. The combustion could be transferred from detonation to flame propagation. For methanol mixture, the combustion process could be transferred from detonation to weak auto-ignition with low peak pressure and negligible pressure oscillation. These indicate that both propane and methanol mixture could suppress detonation and thus suppress super-knock effectively, even if pre-ignition occurs. It could be an effective and practical control strategy to protect modern highly turbocharged spark ignition engines.