The effect of in-cylinder flow and turbulence on HCCI operation

The effect of in-cylinder flow and turbulence on HCCI operation has been experimentally studied by changing the combustion chamber geometry and the swirl ratio. Four different levels of turbulence were achieved, by altering the swirl ratio both for a high turbulent square bowl-in-piston combustion chamber and for a low turbulent disc combustion chamber. The swirl ratio was altered by using different inlet port designs. The results showed that the combustion chamber geometry plays a large role in HCCI combustion. With the same operating conditions, the combustion duration for the square bowl-in-piston combustion chamber was much longer compared to the disc combustion chamber. On the other hand, a moderate change in swirl ratio proved to have only modest effect on the combustion process. With early combustion timing, the gross indicated efficiency was higher when the square bowl-in-piston combustion chamber. Although, with late combustion timing, the disc combustion chamber gave the highest efficiency. When the disc combustion was used, the indicated efficiency was rather unaffected by a change in swirl ratio. However, with the square bowl-in-piston combustion chamber a somewhat higher indicated efficiency was obtained with the low swirl ratio.