Methanol-gasoline DFSI (dual-fuel spark ignition) combustion with dual-injection for engine knock suppression

This paper presents an experimental study on the M-G DFSI (methanol-gasoline dual-fuel spark ignition) combustion for knock suppression in a gasoline engine with high compression ratio. M-G DFSI is organized using a port-injection of high oxygenated, high latent heat and high octane number fuel to suppress knock and a direct injection of high energy density and high volatility fuel to extend high load. The effects of methanol/gasoline ratio of DFSI (dual-fuel spark ignition) under stoichiometric condition on engine knock suppression were investigated. The comparative analysis of the fuel economy and combustion characteristics of the enriched gasoline combustion and Methanol-Gasoline DFSI were conducted. When the enriched gasoline mixture is at the equivalence air/fuel ratio (λ) of 0.8, the high load can be extended by 13.6% but the ISEC (indicated specific energy consumption) increases by 23.8%. On the contrary, when using M-G DFSI with 54% methanol, the high load can be extended by 11.7% and the ISEC decreases by 14.1%. Compared with gasoline enriched combustion, the ignition delay of DFSI with 54% methanol is about 1° CA longer, while the peak pressure (Pmax) and the maximum pressure rise rate (PRRmax) of the DFSI are 5.0 bar and 0.5 bar/°CA higher. In addition, the crank angle of 50% heat release (CA50), the crank angle of Pmax and the crank angle of PRRmax are about 3° CA earlier. This also the case as the mass fraction of methanol increases. It can be shown that Methanol-Gasoline DFSI is a potential combustion concept to suppress engine knock and extend the high load limit for high efficient utilization and alternative fuel practical application of gasoline engine.