Premixed charge compression ignition (PCCI), an advanced mode combustion strategy, promises to simultaneously deliver the fuel efficiency of diesel combustion and the ultralow NO x emissions that usually require advanced exhaust aftertreatment. A flexible, computationally efficient, and whole engine simulation model for a 2007 6.7 l diesel engine with exhaust gas recirculation (EGR), variable geometry turbocharging (VGT), and common rail fuel injection was validated after extensive experimentation. This model was used to develop strategies for highly fuel-efficient and ultralow 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 (multipulse fuel injectors, EGR valve, and VGT) and flexible intake valve closure modulation, which dictates the effective compression ratio. 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.