Modelling of HCCI Engines: Comparison of Single-zone, Multi-zone and Test Data

This paper presents a modeling study of a gasoline HCCI engine using a single-zone and a multi-zone engine combustion models coupled with the CHEMKIN chemical kinetics solver for the closed part of the cycle. These combustion models are subsequently combined with a 1-D gas dynamics engine cycle simulation code which calculates the engine gas exchange to supply the boundary conditions for the in-cylinder simulation and also predicts engine performance. The simulated in-cylinder pressure history and charge composition at the time of exhaust valve opening are compared with the data from a parallel engine experimental project.

Although the single-zone model is useful for parameter studies by predicting the trend of auto-ignition timing variations as the result of the effect of engine operating conditions, the matching of simulated and test data is good perhaps only if the mixture and temperature distributions in the cylinder are uniform. The present work shows that for a gasoline direct injection engine, especially with negative valve overlapping for EGR trapping, it can neither accurately simulate the pressure rise rate nor correctly predict the auto-ignition timing. It is demonstrated that the heterogeneous mixtures with varied temperature distributions associated with different engine operating conditions tend to autoignite earlier as mixtures in high temperature zones ignite first and accelerate ignition process of the rest. The multi-zone model developed in the present study shows significant improvement over the single-zone model in terms of the agreement between the modeled results and test data. The combination of chemical kinetics combustion models and an external gas dynamics engine code in an iterative loop has demonstrated capability in assisting the study of engine performance under steady-state and also in transition of combustion mode conditions.