A Dual-Fuel Model of Flame Initiation and Propagation for Modelling Heavy-Duty Engines with the G-Equation

We propose a novel dual-fuel combustion model for simulating heavy-duty engines with the G-Equation. Dual-Fuel combustion strategies in such engines features direct injection of a high-reactivity fuel into a lean, premixed chamber which has a high resistance to autoignition. Distinct combustion modes are present: the DI fuel auto-ignites following chemical ignition delay after spray vaporization and mixing; a reactive front is formed on its surroundings; it develops into a well-structured turbulent flame, which propagates within the premixed charge. Either direct chemistry or the flame-propagation approach (G- Equation), taken alone, do not produce accurate results. The proposed Dual-Fuel model decides what regions of the combustion chamber should be simulated with either approach, according to the local flame state; and acts as a “kernel” model for the G- Equation model. Direct chemistry is run in the regions where a premixed front is not present. The “kernel” front is identified using a fast, sparse Chemical Explosive Mode Analysis (CEMA), and a novel on-the- fly spontaneous flame speed formulation. The G=0 surface is initialized when the front is thick enough to be well-represented on the computational grid; it is then advanced using the G-Equation model with a multi-component flame speed. The model is validated against optical experiments which feature direct- injected Diesel and premixed natural gas. Good accuracy and reliability are seen identifying the flame initiation region, with little user input.