Abstract
A parametric study of automotive diesel combustion in a low-temperature, late-injection combustion regime is described. Injection pressure was varied from 600-1200 bar, swirl ratio from 1.44-7.12, and intake temperature from 30-110°C. In-cylinder pressure records, heat release analysis, spatially-integrated soot luminosity, and images of the spatial distribution of combustion luminosity are employed to study the influence of these parameters on the combustion and soot formation/oxidation processes. Load points of 3 and 6 bar gross IMEP at 1500 RPM and an O_2 concentration of 0.15 are considered. Increased injection pressure is found to enhance the early mixture formation process, resulting in increased peak apparent heat release, generally decreased soot luminosity, and modestly increased light-load soot oxidation rates. At lower injection pressures, more soot luminosity is observed from the squish volume. In contrast, variation of flow swirl impacts the latter half of the combustion process, and affects the initial combustion only slightly. An optimum Ricardo swirl ratio of roughly 3 is found for best moderate-load efficiency and soot oxidation. A marked reduction in early heat release rates and peak soot luminosity is observed with decreased intake temperature. Nevertheless, significant incylinder soot luminosity is observed even at the lowest intake temperatures, indicating that complete suppression of incylinder soot formation is difficult with the fuel injection and combustion system characteristics employed.
