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. In this work we explore the potential of partial fuel stratification (PFS) to control the combustion timing by altering the kinetic rates of autoignition. The PFS was produced by a double direct injection (DDI) process using a GDI fuel injector, with 70 – 80% of the fuel being directly injected early in the intake stroke (start of injection = 60° aTDC intake) and the remainder being injected during the compression stroke (200 – 325° aTDC intake, 160 – 35° bTDC compression). The amount of mixture stratification was varied by changing the late-DI timing and/or late-DI fuel fraction. Experiments were conducted in a single-cylinder LTGC research engine at 1200 rpm, for intake pressures from 1.0 – 2.0 bar absolute, using a research-grade E10 gasoline (RD5-87) designed to be representative of regular-grade market gasolines. The results show that DDI-PFS is very effective for combustion-timing control. By varying the late-DI timing, CA50 could be adjusted as much a 8.5° CA, from near the misfire limit (overly retarded CA50) to well beyond the acceptable knock/ringing limit (overly advanced CA50). Similar injection-timing control of CA50 is demonstrated for all intake pressures from 2.0 bar down to 1.0 bar, and for compression ratios of both 14:1 and 16:1. NOx and soot emissions remained low for all conditions studied. In addition to combustion-timing control, DDI-PFS is found to improve robustness and stability at selected conditions.