Assessment of the Effects of Intake Temperature and Injector Structure on the Combustion Characteristics of Direct-Injection Spark-Ignition Methanol Engines

In this article, to address the issues of slower droplet evaporation and fuel mixing inhomogeneity caused by the high latent heat of vaporization of methanol, the effects of the number of nozzle holes and spray cone angle (θ_sca) on the combustion characteristics of a direct-injection spark-ignition methanol engine are numerically investigated at different intake temperatures (T_int) under constant injection pressures. In the results, it is indicated that the maximum-indicated thermal efficiency (ITE) is 48.01% at 8 holes and a T_int of 328 K. Although the ITE at 298 K with 8 holes is 1.42% lower than 328 K, NOx emissions and ringing intensity (RI) are reduced by 90.46% and 90.61%, respectively. Simultaneously, emissions of CO, hydrocarbon (HC), Soot, unburned methanol, and formaldehyde remain at a low level. Second, there exists an optimal θ_sca at different holes, thus obtaining the best fuel economy and emissions. The maximum ITE is 48.1% at 8 holes and a θ_sca of 26°. Finally, under the same energy input and parameter, compared with the diesel engine of the optimal start of injection, the ITE of the optimized methanol engine is increased by 1.65%, and the RI, NOx, HC, CO, and Soot emissions are reduced by 98.58%, 77.85%, 99.35%, 85.71%, and 78.38%, respectively.