Mixture formation and combustion characteristics of directly injected LPG spray

Abstract

It has been recognized that alternative fuels such as liquid petroleum gas (LPG) has less polluting combustion characteristics than diesel fuel. Direct-injection stratified-charge combustion LPG engines with spark-ignition can potentially replace conventional diesel engines by achieving a more efficient combustion with less pollution. However, there are many unknowns regarding LPG spray mixture formation and combustion in the engine cylinder thus making the development of high-efficiency LPG engines difficult. In this study, LPG was injected into a high pressure and temperature atmosphere inside a constant volume chamber to reproduce the stratification processes in the engine cylinder. The spray was made to hit an impingement wall with a similar profile as a piston bowl. Spray images were taken using the Schlieren and laser induced fluorescence (LIF) method to analyze spray penetration and evaporation characteristics. Combustion characteristics were examined visually by taking simultaneous images of the flame and OH radical formed during combustion. Numerical calculations using the KIVA-3 code was performed to predict mixture formation and combustion of LPG. The results showed that the LPG mixture moved along the impingement wall eventually reaching the spark plug location. The OH radical rose sharply and decreased gradually when combustion occurred vigorously. The predicted results from numerical calculations showed favorable agreement with measurements.