Gas-wall heat flux analysis on PCI combustion by using the one-dimensional model (Effect of change in heat loss under transient operation)

Abstract

Premixed Compression Ignition (PCI) engine has a potential to improve transient performance as well as exhaust emissions. In this paper, a one-dimensional engine model combined with a heat transfer model is used to analyze heat flux between in-cylinder gas and cylinder wall under steady-state operation and transient characteristics of heat loss and torque under transient operation. PCI combustion is initiated by spontaneous multi-point ignition, generating high in-cylinder pressure. According to Woschni equation, heat transfer coefficient is high under high in-cylinder pressure condition. In addition, the rapid combustion near the top dead center which can be seen under PCI combustion causes high in-cylinder gas temperature. Consequently, the temperature difference between in-cylinder gas and cylinder wall is large under PCI combustion. These phenomena which can be seen under PCI combustion induce a higher heat flux than diesel combustion. The analysis results of transient operation show that a slight difference in the ignition delay due to wall surface temperature has a small effect on the combustion characteristics under PCI combustion and it contributes to the improvement of convergence performance. The present results suggest that transient performance of torque will be improved by applying PCI combustion.