An Investigation of Different Ported Fuel Injection Strategies and Thermal Stratification in HCCI Engines Using Chemiluminescence Imaging 2010-01-0163

The purpose of this study was to gain a better understanding of the effects of port fuel injection strategies and thermal stratification on the HCCI combustion processes. Experiments were conducted in a single-cylinder HCCI engine modified with windows in the combustion chamber for optical access. 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.

The experimental data consisting of the in-cylinder pressure, heat release rate, chemiluminescence images all indicate that the different port fuel injection strategies result in different charge distributions in the combustion chamber, and thus affect the auto-ignition timing, chemiluminescence intensity, and combustion processes. Under higher intake temperature conditions, the injection strategies have less effect on the combustion processes due to improved mixing. The intake temperature is a more important factor affect in a mixture and combustion process. Fuel injection duration the intake stroke and the intake valve opening phase (-300 °ATDC) results in a more homogeneous charge mixture, which is beneficial to combustion and fuel economy. With changing coolant temperature and intake temperature, the in-cylinder temperature distribution will be altered leading to different combustion processes. Enhanced thermal stratification has the potential for smoothing pressure-rise rates. At low loads, increased thermal stratification is worse because more quenching maybe occur at the cooler regions in the cylinder. Therefore, less thermal stratification and higher in-cylinder temperature are better for low load operation.