Evaluation of non-premixed combustion and fuel spray models for in-cylinder diesel engine simulation

Computational Fluid Dynamics (CFD) study of light-duty automotive diesel engines affords invaluable insights into in-cylinder conditions and processes, which greatly expands on the very limited detail provided by engine-out measurements of exhaust emissions. For the simulation to be successful, accuracy and robustness of the physical sub-models are crucial. The purpose of this feasibility study is to appraise the non-premixed combustion and fuel spray CFD sub-models for in-cylinder diesel engine simulation on a FLUENT 6.3.26 platform. Simulation results are compared against data from parallel experimental test-bed studies in terms of pressure traces, heat release curves and tailpipe values of NOx and soot levels. Heat release rate and pressure trace from the computations are found to be within a reasonable error limit of 10%. Simulated heat released plots are able to capture the general trend of premixed and mixing-controlled diesel combustion phases. Ignition delay period for the main combustion event is well predicted, although the calculated ignition delay period for pilot combustion is 7–10° crank angle degrees earlier for all the test cases. The variations for exhaust soot and NO when the timing of start of injection is changed are reproduced successfully. CFD modelling, when used in conjunction with experimental studies is proven to be particularly effective in elucidating physical details of in-cylinder processes.