Gasoline DICI Engine Operation in the LTC Regime Using Triple- Pulse Injection 2012-01-1131

An investigation of high speed direct injection (DI) compression ignition (CI) engine combustion fueled with gasoline injected using a triple-pulse strategy in the low temperature combustion (LTC) regime is presented. This work aims to extend the operation ranges for a light-duty diesel engine, operating on gasoline, that have been identified in previous work via extended controllability of the injection process. The single-cylinder engine (SCE) was operated at full load (16 bar IMEP, 2500 rev/min) and computational simulations of the in-cylinder processes were performed using a multi-dimensional CFD code, KIVA-ERC-Chemkin, that features improved sub-models and the Chemkin library. The oxidation chemistry of the fuel was calculated using a reduced mechanism for primary reference fuel combustion chosen to match ignition characteristics of the gasoline fuel used for the SCE experiments.

With constraints on a minimum allowable combustion efficiency, maximum allowable noise level (pressure rise rate) and maximum allowable NO_x and soot emissions, engine operation ranges were identified as functions of injection timings and the fuel split ratio (i.e., fraction of total fuel injected in each pulse) with triple-pulse injections. Parametric variation of the engine operating ranges were also investigated with respect to initial (i.e., intake) gas temperature, exhaust gas recirculation ratio, intake boost pressure and injection system rail pressure. Following the modeling, engine experiments were performed under conditions identified through analysis of the numerical results in order to confirm the effectiveness of gasoline direct injection compression ignition (GDICI or GCI) operation with triple-pulse injections at full load.

Based on both computational and experimental results, the role of each pulse in GDICI operation was identified in terms of combustion stability, engine performance and emissions. While maintaining similar emissions characteristics to that of the double-pulse injection cases (~0.1 g/kg-f of NO_x and PM, and ~173 g/kW-hr of ISFC), the extension of operable conditions using a triple-pulse injection strategy was successfully achieved.