Transient RCCI Operation in a Light-Duty Multi-Cylinder Engine

Reactivity Controlled Compression Ignition (RCCI) is an engine combustion strategy that utilizes in-cylinder fuel blending to produce low NO_x and PM emissions, while maintaining high thermal efficiency. Previous RCCI steady-state performance studies provided a fundamental understanding of the RCCI combustion process in steady-state, single-cylinder and multi-cylinder engine tests. The current study investigates RCCI and conventional diesel combustion (CDC) operation in a light-duty multi-cylinder engine over transient operating conditions. In this study, a high-bandwidth, transient-capable engine test cell was used and multi-cylinder engine RCCI combustion is compared to CDC over a step load change from 1 to 4 bar BMEP at 1,500 rev/min. The engine experiments consisted of in-cylinder fuel blending using port fuel-injection (PFI) of gasoline and early-cycle, direct-injection (DI) of ultra-low sulfur diesel (ULSD) for the RCCI tests and used the same ULSD for the CDC tests. Over the step load change, both combustion modes were compared for combustion performance and emissions using fast response HC, NO and PM instrumentation. Similar intake pressures were used for both combustion modes to explore the robustness of the RCCI combustion strategy using real-world operating conditions with production viable hardware. It was found that the engine was able to operate with RCCI combustion with lower engine-out PM and NO but increased HC and CO emissions than CDC over the specified transient engine operating conditions using either open- or closed-loop feedback control of the combustion phasing.