An Investigation of Different Combustion Chamber Configuration, Intake Temperature, and Coolant Temperature in a HCCI Optical Engine 2011-01-1765

The influence of different combustion chamber configuration, intake temperature, and coolant temperature on HCCI combustion processes were investigated in a single-cylinder optical engine. Two-dimensional images of the chemiluminescence were captured using an intensified CCD camera in order to understand the spatial distribution of the combustion. N-heptane was used as the test fuel. Three combustion chamber geometries with different squish lip, salient, orthogonal, reentrant shape, referred as V-type, H-type, and A-type respectively, were used in this study. Intake temperature was set to 65°C and 95°C, while coolant temperature was set to 85°C. The experimental data consisting of the in-cylinder pressure, heat release rate, chemiluminescence images all indicated that the different combustion chamber geometries result in different turbulence intensity in the combustion chamber, and thus affect the auto-ignition timing, chemiluminescence intensity, and combustion processes. For the A-type combustion chamber, the high temperature autoignition occurred in the center of chamber, while autoignition location for the V-type combustion chamber was more dispersive and was closer to the chamber wall. Heat release rate and pressure rise rate was the highest and combustion duration was the shortest for the V-type combustion chamber among the three cases, while the A-type combustion chamber induced a higher turbulence intensity, which enhanced the temperature inhomogeneities in the piston bowl, leading to moderate pressure rise rate and heat release rate.