Multi-dimensional modelling of spray, in-cylinder air motion and fuel-air mixing in a direct-injection engine

In this work, three-dimensional fuel-air mixing inside a conventional spark ignition engine cylinder is simulated under direct injection conditions. The motivation is to explore retrofitting of conventional engines for direct injection to take advantage of low emissions and high thermal efficiency of the direct injection concept. Fuel-air mixing is studied at different loads by developing and applying a model based on the Lagrangian-drop and Eulerian-fluid (LDEF) procedure for modelling the two-phase flow. The Taylor Analogy Breakup (TAB) model for modelling the hollow cone spray and appropriate models for droplet impingement, drag and evaporation are used. Moving boundary algorithm and two-way interaction between both phases are implemented. Fuel injection timing and quantity is varied with load. Results show that near-stoichiometric fuel-air ratio region is observed at different locations depending on the load. The model developed serves to predict the fuel-air mixing spatially and temporally, and hence is a useful tool in design and optimization of direct injection engines with regards to injector and spark plug locations. Simulations over a range of speed and load indicate the need for a novel ignition strategy involving dual spark plugs and also provide guidelines in deciding spark plug locations.