CFD-Guided Combustion Strategy Development for a Higher Reactivity Gasoline in a Light-Duty Gasoline Compression Ignition Engine 2017-01-0740

The current study utilized 3-D computational fluid dynamics (CFD) combustion analysis to guide the development of a viable full load range combustion strategy in a light-duty gasoline compression ignition (GCI) engine. A higher reactivity gasoline that has a research octane number (RON) of 70 was used for the combustion strategy development. The engine has a geometric compression ratio of 14.5 with a piston bowl designed to accommodate different combustion strategies and injector spray patterns. Detailed combustion optimization was focused on 6 and 18 bar gross indicated mean effective pressure (IMEPg) at 1500 rpm through a Design of Experiments approach. Two different strategies were investigated: (a) a late triggering fuel injection with a wide spray angle (combustion strategy #1); and (b) an early triggering fuel injection with a narrow spray angle (combustion strategy #2). Combustion strategy #1 preferred a higher swirl ratio, while a lower swirl ratio was more desired for combustion strategy #2. At 6 bar IMEPg, high efficiency clean GCI operation can be achieved using both strategies. When increasing the engine load to 18 bar IMEPg, combustion strategy #2 was limited by excessive pressure rise rate. In contrast, by carefully balancing between premixed combustion and mixing-controlled combustion, combustion strategy #1 led to fuel-efficient mixed-mode combustion operation. By utilizing this combustion strategy, full load operation at 24 bar IMEPg was achieved while meeting all the performance requirements. Both combustion strategies favored a larger number of nozzle holes. Combustion strategy #1 generally showed a stronger preference towards higher injection pressure.