Modeling the Effects of Variable Intake Valve Timing on Diesel HCCI Combustion at Varying Load, Speed and Boost Pressures

Abstract

It is well known that homogeneous charge compression ignition (HCCI) operated engines have the potential to provide the efficiency of a typical diesel engine, but with very low NOx and Particulate Matter (PM) emissions. One of the main challenges with this type of engine, however, is that it can be difficult to control the combustion event, especially at high loads. The development of Variable Valve Timing (VVT) technology may offer an important advantage in the ability to control HCCI combustion. This work investigates the potential of using late intake valve closure times to delay auto-ignition and to expand the HCCI operation range through proper combustion control. A multi-dimensional KIVA/Chemkin model is used in conjunction with detailed chemical kinetics, based on an available n-heptane mechanism. The model is used to evaluate the effectiveness of late intake valve times as load, speed, and boost pressure conditions are varied. Furthermore, a larger understanding of diesel HCCI combustion is sought by investigating the major parameters affecting combustion control under these various operating conditions.