Numerical study of knock occurrence in an internal combustion engine using VVT strategy and different compression ratios

The adoption of high compression ratios when designing an internal combustion engine is often used to improve thermal efficiency. However, compression ratio cannot be enhanced indefinitely since elevated pressures and temperatures inside the combustion chamber may cause knock. In view of this issue, it is important to have an accurate knowledge about the conditions in which the probability of knock occurrence is high to preserve engine integrity and achieve the best performance. In addition, if numerical tools are available for this type of analysis, time and experimentation costs can be avoided. Based on this idea, this paper presents a numerical tridimensional study of knock occurrence in a spark ignition three-cylinder engine operating with different compression ratios and late intake valve closing. By means of this analysis, it was possible to represent the knock phenomenon and evaluate its main causes, as well as investigate flow patterns, mixture formation, and combustion process, besides the effect of spark advance on knock occurrence.