Experimental Investigation of Light-Medium Load Operating Sensitivity in a Gasoline Compression Ignition (GCI) Light-Duty Diesel Engine 2013-01-0896

The light-medium load operating range (4-7 bar net IMEP) presents many challenges for advanced low temperature combustion strategies utilizing low cetane fuels (specifically, 87-octane gasoline) in light-duty, high-speed engines. The overly lean overall air-fuel ratio (Φ≺0.4) sometimes requires unrealistically high inlet temperatures and/or high inlet boost conditions to initiate autoignition at engine speeds in excess of 1500 RPM. The objective of this work is to identify and quantify the effects of variation in input parameters on overall engine operation. Input parameters including inlet temperature, inlet pressure, injection timing/duration, injection pressure, and engine speed were varied in a ~0.5L single-cylinder engine based on a production General Motors 1.9L 4-cylinder high-speed diesel engine.

With constraints of combustion efficiency, noise level (pressure rise rate) and emissions, engine operation sensitivity due to changes in inlet temperature between 50-90C was first examined for fixed fueling rates. This experiment was then repeated at different inlet pressures and engine speeds. Finally, constant load experiments were performed in which perturbations in injection strategies (timing, duration, and pressure) were executed to assess overall system sensitivity. These experiments revealed primary and secondary effects with respect to changes in engine operation. In addition, an assessment of combustion robustness was made as well.

Based on the results, we conclude that input parameters can be effectively manipulated to maintain low NOx emissions ≺0.6 g/kg-fuel with good combustion stability (COV of IMEP ≺3%) over a wide inlet temperature range. Further optimization (with respect to combustion efficiency and CO/UHC emissions) was realized with additional adjustment of these input parameters. Interestingly, gross ISFC remained relatively unaffected by changes in input parameters (185-190 g/kWh). This last observation leads to the assessment that GCI combustion can provide robust, high-fuel-efficiency, low-emissions light-medium load operation in a light-duty engine application.