Development of a mechanism-dynamic-selection turbulent premixed combustion model with application to gasoline engine combustion and emissions simulation

Abstract

In order to overcome the drawback (tuning reaction rate coefficients) of using a single mechanism in the chemical-kinetics-based turbulent premixed combustion modelling approach, a mechanism-dynamic-selection turbulent premixed combustion model has been developed, validated, and successfully applied to the combustion and emissions simulation of spark ignition gasoline engines. In this new model, based on the local thermal and turbulent conditions of any preheat cell, a certain chemical kinetic mechanism which can achieve the target ratio of turbulent flame speed to laminar flame speed is selected. To realise this goal, based on the laminar flame speed sensitivity analysis of an improved eTRF (ethanol toluene reference fuel) base chemical kinetic mechanism, a derived mechanism library has been generated. Based on enough experimental and DNS (direct numerical simulation) data of S T/S L, a mechanism selection database (mechanism as a function of Borghi-Peters coordinates) has been constructed and implemented into a CFD (computational fluid dynamics) code, also a classification scheme for identifying unburned, preheat, flame front, and burned zones of a combustion domain has been developed and implemented into the CFD code. The developed mechanism-dynamic-selection turbulent premixed combustion model has been validated using the combustion in a spherical constant volume and applied to the prediction of combustion and emissions of a spark ignition gasoline engine under transient cold start process. Validation results show that, without tuning any model parameters, the base mechanism, the derived mechanism library, the mechanism selection function, the classification scheme, as well as a simulation setup strategy for modelling engine transient cold start process, have good prediction performances and are practical for engine combustion and emissions simulation.