The Effects of Intake Flow Swirl on the Combustion Characteristics of Hydrogen Fueled HCCI Engines

This paper describes the effects of the initial intake flow swirl on the combustion process of hydrogen-air homogeneous mixtures in HCCI engines. CFD KIVA3 code incorporated with detailed chemical kinetics was employed. The effects on the development and extent of non-uniformities in velocity, pressure, and temperature within the cylinder charge were investigated. Moreover, the effects of the initial flow swirl ratio values on the onset of autoignition and its timing, combustion duration, NOx emissions, and the onset of knock were evaluated. It is shown that an increase in the initial flow swirl ratio or speed lengthens the delay period for autoignition and extends the combustion period while reducing NOx emissions. There are optimum values of the initial swirl ratio and engine speed for a certain set of engine operating conditions that can achieve high thermal efficiencies and low NOx emissions while reducing the tendency to knock.