Large-Eddy Simulations of Diesel-Assisted Ignition of Methanol Spray Under Engine-Relevant Conditions

Abstract Methanol, a renewable low-carbon fuel with potential for future engines, faces combustion issues and therefore requires pilot diesel injection for reliable ignition. A large-eddy simulation of methanol/n-heptane dual direct injection was conducted under engine-like conditions. Liquid n-heptane was injected into the methanol spray to serve as an ignition source. The effects of injection angles and ambient temperatures on the dual-fuel combustion process were investigated. Results showed that a too small injection angle (θ) delayed the interaction between the n-heptane spray flame and the nonreacting methanol spray, thus prolonging the ignition process for methanol. In contrast, a too large θ suppressed the evaporation and early oxidization of n-heptane due to the direct injection into the low-temperature region before the onset of high-temperature combustion. An angle of 15 deg for θ could provide suitable combustion phase of methanol at a high temperature of 1100 K. Due to the ignition assistance from n-heptane, the ambient gas could be decreased to 950 K for successful ignition. However, ignition failure occurred at 900 K due to the early interaction before the formation of high-temperature combustion due to the suppression from cold methanol. By reducing the injection angle to 5 deg, the delay of the interaction can provide stable ignition with the assistance of n-heptane.