Effects of Fuel Property Changes on Heavy-Duty HCCI Combustion

Homogeneous charge compression ignition (HCCI) offers the potential for significant improvements in efficiency with a substantial reduction in emissions. However, achieving heavy-duty (HD) HCCI engine operation at practical loads and speeds presents numerous technical challenges. Successful expansion of the HCCI operating range to include the full range of load and speed must be accomplished while maintaining proper combustion phasing, control of maximum cylinder pressure and pressure rise rates, and low emissions of NOx and particulate matter (PM). Significant progress in this endeavour has been made through a collaborative research effort between Caterpillar and ExxonMobil. This paper evaluates fuel effects on HCCI engine operating range and emissions. Test fuels were developed in the gasoline and diesel boiling range covering a broad range of ignition quality, fuel chemistry, and volatility. All fuels were evaluated in a Caterpillar 3401E Single Cylinder Oil Test Engine (SCOTE) under HCCI conditions. Exhaust emissions and engine performance were measured as a function of key engine variables, including engine speed, amount of exhaust gas recirculation (EGR), and fuel injection timing. The results show that the proper combination of fuel quality and engine conditions can achieve heavy-duty HCCI operation over a broad load range while realizing significant emission reductions. At the 12:1 engine compression ratio (CR) tested, it was found that fuels with ignitability intermediate between current gasoline and diesel fuels provided the maximum high load operability.