3-D CFD combustion and knocking prediction in pre-chamber gas engines

Simple, fast running 3-D CFD models were developed in this work for layout of modern pre-chamber natural gas engines and were validated against experiments on a single cylinder research engine. The Charge Motion Design (CMD) process predicts burn durations without a combustion model was calibrated based on measurements from two engines. The 3-D CFD gas exchange simulations were run to calculate the scavenging and the mixture formation considering the shape of the PC. A prescribed heat release combustion model, which can calculate the 3-D flame front propagation for given input of heat release rate without any calibration, was used in this work. Three representative cycles from the measurements were simulated to account for cyclic fluctuations. The heat transfer from the simulations correlated well with the thermocouple measurements in the PC body. A single-scalar NOx model based on tabulated data was programmed and validated against measurements. A 3-D CFD auto-ignition model was developed based on the simplified knock integral approach with dependency on the pressure, temperature, equilibrium ratio and the rest-gas content. The constants of the integral were calibrated to the Saudi Aramco 2.0 detailed chemistry mechanism. The simulation could predict the knock onset and showed correlation to the knock intensity. To transfer the results of the burn duration prediction from the CMD process to the non-predictive combustion model, a method to generate the heat release curves and to determine the cycle to cycle variations based on a statistical analysis was developed