Investigation of the Effect of Injection and Control Strategies on Combustion Instability in Reactivity Controlled Compression Ignition (RCCI) Engines

This paper uses detailed CFD modeling with the KIVA-CHEMKIN code to investigate the influence of injection timing, combustion phasing and operating conditions on combustion instability. Using detailed computational fluid dynamics (CFD) simulations, a large design of experiments (DOE) is performed with small perturbations in the intake and fueling conditions. A response surface model (RSM) is then fit to the DOE results to predict cycle-to-cycle combustion instability. Injection timing had significant tradeoffs between engine efficiency, emissions and combustion instability. Near TDC injection timing can significantly reduce combustion instability, but the emissions and efficiency drop to close to conventional diesel combustion (CDC) levels. The fuel split between the two DI injections has very little effect on combustion instability. Increasing EGR rate, while making adjustments to maintain combustion phasing, can significantly reduce PPRR variation until the engine is on the verge of misfiring. Combustion phasing has a very large impact on combustion instability. More advanced phasing is much more stable, but produces high peak pressure rise rates, higher NOx levels, and can be less efficient due to increased heat transfer losses. The results of this study identify operating parameters that can significantly improve the combustion stability of dual-fuel RCCI engines.