Modeling the Effect of Swirl on Turbulence Intensity and Burn Rate in S.I. Engines and Comparison with Experiment

An Engine Simulation Model was used to study the effect of in-cylinder swirl level on turbulence intensity and burn rate while holding the inducted kinetic energy constant. Experimental measurements of burn rate for three different swirl levels were obtained and compared with model predictions. The turbulence model used previously did not include wall shear effects and showed little enhancement of turbulence due to swirl, causing small changes in predicted burn rate when the swirl level was changed. An improved turbulence model is proposed which includes production of turbulence due to wall shear effects.

Turbulence intensity predictions from the improved model resulted in excellent agreement between the measured and predicted burn rates as swirl level was changed. In addition, the model was used to predict the effect of swirl levels on ISFC. Results showed that ISFC changes were overall small for the range of swirl levels considered.