Three-dimensional computation of the effects of the swirl ratio in direct-injection diesel engines on NO{sub}x and soot emissions

摘要

Three-dimensional computation has been applied to analyze combustion and emission characteristics in direct-injection diesel engines. A computational code called TurboKIVA was used to investigate the effects of the swirl ratio, one of the fundamental factors related to combustion control, on combustion characteristics and NO{sub}x and soot emissions. The code was first modified to calculate soot formation and oxidation and the precise behavior of fuel drops on the combustion chamber wall. As a result of improving calculation accuracy, good agreement was obtained between the measured and predicted pressure, heat release rate and NO{sub}x and soot emissions. Using this modified version of TurboKIVA, the effects of the swirl ratio on NO{sub}x and soot emissions were investigated. The computational results showed that soot emissions were reduced with a higher swirl ratio. However, a further increase in the swirl ratio produced greater soot emissions. A careful examination of the fuel spray formation and air-fuel mixing process revealed the reasons for the increased soot emissions. Based on these results, this paper describes the effects of the swirl ratio on combustion characteristics and NO{sub}x and soot emissions and the mechanism of soot formation and oxidation in DI diesel engines.