Numerical Simulation of the Combustion Process of a High EGR, High Injection Pressure, Heavy Duty Diesel Engine

To comply with Stage IV emission standard for off-road engines, Kohler Engines has developed the 100kW rated KDI 3.4 liters diesel engine, equipped with DOC and SCR. Based on this engine, a research project in collaboration between Kohler Engines, Ricardo, Denso and Politecnico di Torino was carried out to exploit the potential of new technologies to meet the Stage IV and beyond emission standards.The prototype engine was equipped with a low pressure cooled EGR system, two stage turbocharger, high pressure fuel injection system capable of very high injection pressure and DOC+DPF aftertreatment system. Since the Stage IV emission standard sets a 0.4 g/kWh NOx limit for the steady state test cycle (NRSC), that includes full load operating conditions, the engine must be operated with very high EGR rates (above 30%) at very high load. As a consequence, the low air to fuel ratio and the risk of high soot emissions must be handled by means of high fuel injection pressure and proper injection patterns.In this context, the DIPulse multizone predictive combustion model developed by Gamma Technologies was extensively employed to support the engine calibration and the hardware selection processes. After populating the injection rate map starting from a limited set of measurements, the model was then calibrated to simulate the combustion process with extremely high injection pressures and EGR rates, achieving a very good correlation with the experimental data in terms of burn rates, engine performance parameters and NOx emissions. In this way a kind of “virtual test rig” was obtained, on which the effects of different injection patterns and hardware components could be analyzed, thus significantly shortening the hardware selection and calibration activities on the test bench to achieve the project targets.