Computational investigation of a methanol compression ignition engine assisted by a glow plug

Abstract

This work explores the feasibility of pure methanol combustion in a light-duty diesel engine assisted by a glow plug (GP). The simulations represented a mild engine load with an indicated mean effective pressure of 7 bar. An extensive computational study was conducted, and the successful operation of the pure methanol compression ignition engine was demonstrated. The effects of the GP position, spray umbrella angle, the relative angle (RA) between the glow plug and jet trajectory, and the injection strategy on the engine performance were evaluated. The autoignition of methanol-air mixture was found to primarily occur at an equivalence ratio between 0.2 and 0.4. However, an even richer mixture accompanied the lower temperature due to intense heat absorption of evaporation, significantly prolonging the ignition delay. Therefore, to improve the ignition and combustion heat release processes, RA was optimized to adequately control the mixture distribution around the GP. At each position of the GP, the optimum RA differed due to the complex flow and air-fuel mixing within the combustion chamber, which became smaller (from 12.5° to 5°) when the GP was moved anticlockwise from the intake port to the exhaust port regions. Furthermore, a split injection strategy was proposed to ensure the successful ignition of the methanol jets. The engine performance exhibited a high sensitivity to the pilot and main injection timings. A small pilot mass fraction of no higher than 20% was recommended to mitigate fuel jet-GP interaction and fuel impingement in the squish region.