Improving the NOX-CO2 Trade-Off of an HCCI Engine Using a Multi-Hole Injector
The combustion and emission performance of two high-pressure GDI-type injectors are compared in an automotive HCCI engine during low-load, stratified operation. One of these, an 8-hole injector with 70° spray angle, provides significant reduction in NOX emissions at a given fuel-to-CO2 conversion efficiency (i.e., an improved NOX-CO2 trade-off) compared to the other, a 53° swirl injector. In contrast, attempts to enhance the NOX-CO2 trade-off using alternate charge-stratification strategies such as split injection and high intake velocity are shown to be less successful. The 8-hole and swirl injectors are also compared using the optical techniques of Mie scattering (spray visualization), laser-induced fluorescence imaging (fuel distribution measurement), and direct combustion imaging. The resulting data suggest two possible explanations for the superior performance of the 8-hole injector.