A Comprehensive Knock Model for Application in Gas Engines

A predictive knock model that utilizes a phenomenological modeling approach has been developed for predicting the onset of knock in gas engines. Several physical models have been developed and incorporated into WAVE, a comprehensive engine simulation code, including 1) a spatially resolved end gas thermodynamics model; 2) a model for calculating the chemical reaction rates of the reactants in the unburned zone; and 3) a model for approximating the heat transfer between the two-zone combustion model and end gas reaction model.

The established predictive knock model has been demonstrated and validated against experimental data. A WAVE simulation model of the Caterpillar G3508 engine was created and used to predict engine knock over a range of fuels, spark timing and compression ratios. The computational results are compared to test data which were obtained from G3508 detonation timing test. Overall, good correlation was achieved between measured data by Caterpillar and data predicted by WAVE. Finally, a parametric study was performed to evaluate the effects of compression ratio on engine knock performance. Based on the parametric study performed, the knock limited compression ratio can be identified for the G3508 engine under a specified operating condition.