PCCI Control Authority of a Modern Diesel Engine Outfitted with Flexible Intake Valve Actuation

Premixed charge compression ignition (PCCI), an advanced mode combustion strategy, promises to simultaneously deliver the fuel efficiency of diesel combustion and the ultra-low NO_x emissions that usually require advanced exhaust aftertreatment. A flexible, computationally efficient, whole engine simulation model for a 2007 6.7-liter diesel engine with exhaust gas recirculation (EGR), variable-geometry turbo-charging (VGT), and common rail fuel injection was validated after extensive experimentation. This model was used to develop strategies for highly fuel-efficient, ultra-low NO_x emission PCCI. The primary aim of this modeling investigation is to determine the PCCI control authority present on a modern diesel engine outfitted with both conventional actuators (multi-pulse fuel injectors, an EGR valve, and VGT) and flexible intake valve closure modulation (IVCM) which dictates the effective compression ratio (ECR). The results indicate that early fuel injection coupled with ECR reduction and modest amounts of EGR yield a well-timed PCCI exhibiting 70%+ reductions in NO_x with no fuel consumption penalty over a significant portion of the engine operating range.