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Mixtures of low concentrations of 3-pentanone in iso-octane are used widely in an attempt to obtain quantitative measurements of fuel equivalence ratio in direct-injection, spark-ignition engines. Despite similar boiling temperatures and heats of vaporization, 3-pentanone has been found to evaporate from the mixture more rapidly than the iso-octane. Thus, the signal detected by the planar laser-induced fluorescence (PLIF) diagnostic cannot accurately represent fuel distribution during spray evaporation and air-fuel mixing in an engine. Using an evaporation chamber, we demonstrate the non-steady PLIF signal of the iso-octane/3-pentanone mixture during steady evaporation. Significant improvement in the consistency of the PLIF signal during evaporation is achieved by adding a heavier ketone (3-hexanone) tracer to compensate for the early depletion of the 3-pentanone.

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.