Combustion-Timing Control of Low-Temperature Gasoline Combustion (LTGC) Engines by Using Double Direct-Injections to Control Kinetic Rates 2019-01-1156

Low-temperature gasoline combustion (LTGC) engines can provide high efficiencies and extremely low NOx and particulate emissions, but controlling the combustion timing remains a challenge. This paper explores the potential of Partial Fuel Stratification (PFS) to provide fast control of CA50 in an LTGC engine. Two different compression ratios are used (CR=16:1 and 14:1) that provide high efficiencies and are compatible with mixed-mode SI-LTGC engines. The fuel used is a research grade E10 gasoline (RON 92, MON 85) representative of a regular-grade market gasoline found in the United States. The fuel was supplied with a gasoline-type direct injector (GDI) mounted centrally in the cylinder. To create the PFS, the GDI injector was pulsed twice each engine cycle. First, an injection early in the intake stroke delivered the majority of the fuel (70 - 80%), establishing the minimum equivalence ratio in the charge. Then, a second injection supplied the remainder of the fuel (20 - 30%) at a variable timing during the compression stroke, from 200° to 330°CA (0°CA = TDC-intake, 360°CA = TDC-compression) to provide controlled stratification. For both CRs, second DI timing sweeps were performed for a range of intake pressures from highly boosted to naturally aspirated conditions, allowing the CA50 control authority at each condition to be determined. By varying the late-DI timing, CA50 could be adjusted as much a 12°CA, from near the misfire limit (overly retarded CA50 with COV-IMEPg > 3%) to well beyond the acceptable knock/ringing limit (overly advanced CA50 with RI > 5 MW/m²). For different conditions, the amount of DI timing retard and CA50 advancement was limited by either engine knock, combustion instabilities, or high NOx emissions (NOx > 0.27 g/kWh). For most conditions, approximately 6-8°CA of CA50 control was possible with good stability and acceptable NOx emissions.