Knock Occurrence Prediction and Performance Optimization of a Natural Gas S.I. Engine

Abstract

Natural gas is used as alternative fuel in speak ignition engines in many countries to satisfy air quality standards. Gas engines can be operated in stoichiometric and lean burn condition with different combustion and emission details. In this study a natural gas spark-ignition engine at stoichiometric condition was optimized to avoid knock occurrence. Compression ratio and engine speed were optimized to obtain the lowest fuel consumption accompanied with high power and low emission. A quasi-dimensional two-zone combustion model was developed to simulate combustion and a knocking model was incorporated with main model to predict any auto-ignition that might occur. The model was validated by comparing with available experimental results. Performance parameters and exhaust emissions were also computed by using this model. It was found that using cooled EGR especially at high compression ratios has a key role in reducing NO emission.