Evaluation of the Ethanol-Diesel Spray Interaction during Ignition in a Dual-Fuel DICI Engine Using an Experimentally Validated CFD Model 2021-01-0521

The ignition dynamics of an ethanol-diesel direct injection compression ignition engine is investigated based on 3D RANS simulations. Experimental results of a previous test campaign on a single-cylinder research engine equipped with two direct injectors are used to validate the CFD model. Four reference engine conditions are considered, including split and overlapped injections of ethanol and diesel at low and high load. Combustion driven by the separate direct injection of pure ethanol and diesel as pilot fuel is simulated with AVL Fire and AVL Tabkin adopting the flamelet generated manifold combustion model. The in-cylinder pressure and apparent rate of heat release traces computed in the simulations are found to be consistent with the corresponding experimental results. The influence of several simulation input parameters on ethanol combustion characteristics is evaluated, highlighting a high sensitivity to the initial in-cylinder temperature and a limited impact of the swirl number. The spatial and temporal interaction between ethanol and diesel sprays during ignition is investigated based on simulation results of in-cylinder flow features. Under the engine conditions considered in this study, ethanol ignition is found to originate within the spray plumes adjacent to the burning diesel sprays and to subsequently propagate towards the other ethanol sprays. The peak sequence identified in the ARoHR traces of experiments and simulations corresponds to the ignition sequence of the ethanol sprays. The coupling between experimental and simulation results allowed to achieve a detailed understanding of the ignition dynamics of an ethanol-diesel DICI engine. The validated simulation model will enable the performance evaluation of alternative hardware configurations of the dual-injector system.