Detailed chemical kinetic simulations of homogeneous charge compression ignition engine transients

Abstract

A fast, full-cycle homogeneous charge compression ignition (HCCI) simulator that uses detailed fuel chemistry for the primary reference fuel PRF90 (1036 species and 4238 reactions) is presented and used to study transient engine performance. The numerical predictions are compared with measured data from a single-cylinder HCCI engine that uses residual gas trapping. In particular, the response of the engine to changes in fuelling rate, speed, and phasing of the exhaust valve event is studied. The experimental results are obtained using a Mazda port fuel injected 2.3 l four-cylinder engine that is modified to run in a single-cylinder mode and to allow HCCI operation. The simulator combines a standard cycle simulation software package for the gas exchange processes with a two-zone model of the trapped charge; the combustion in the cylinder is modelled using a detailed chemical kinetics mechanism. To minimize the demand for computational resources, a specialized numerical solver is used that exploits sparsity of the system and allows the simulator to run in 7–8 min per cycle on a desktop computer. The numerical and experimental results are compared. The model predictions for the transient time constants and the changes in gross indicated mean effective pressure (GIMEP) during/after a step change in equivalence ratio, φ, and speed are consistent with experimental data and are accurate enough to be useful for HCCI engine design. The model predictions for the changes in CA50 (the crank angle at which 50 per cent of the cumulative heat release occurs) during transients are less reliable. Ways by which the fidelity of the HCCI transient model predictions could be improved are outlined.