Computational Fluid Dynamics (CFD) modeling of gasoline Direct Injection Spark Ignition (DISI) combustion under normal operating conditions has been discussed in detail using both the detailed chemistry mechanisms and flamelet models (e.g., G-Equation). However, little work has discussed the capability of the existing models to capture DISI combustion under cold-start conditions. Accurate prediction of cold-start behavior involves the efficient use of multiple models: spray modeling to capture the split injection strategies, ignition modeling to capture the effects of the retarded spark timings, combustion modeling to accurately capture the flame travel, and turbulence modeling to capture the effect of decaying turbulent kinetic energy. The retarded spark help generate high heat flux in the exhaust for faster catalyst light-off during cold start; however, the adverse effect is reduced turbulent flame speed due to decaying turbulent kinetic energy. Accordingly, developing an understanding of the turbulence-chemistry interactions is imperative for accurate modeling of combustion under cold start conditions. In the current paper, cold start conditions are validated using both a detailed chemistry model and the G-Equation model. The flame front travel is captured on a Borghi-Peters Diagram to find that the flame travels through corrugated, wrinkled and laminar regimes. The capability of these combustion models in these regimes are to be studied in detail to understand the accuracy in capturing the turbulence-chemistry interactions. The scope of the current paper is limited to the study of model behavior in the laminar regime, which will be shown to be important for DISI cold-start. The detailed chemistry model, with a toluene reference fuel (TRF) mechanism validated for gasoline flame speeds, is found to significantly under-predict the laminar flame speeds because of numerical viscosity effects and discrepancy in capturing molecular diffusion. The cause and effects of such an under-prediction and ways of improvements are presented. 


Challenges of Using Detailed Chemistry Model for Modeling Disi Cold-Start Combustion

Division / Sponsors: 
Internal Combustion Engine Division (ICED)

Paper Proceedings: https://asmedigitalcollection.asme.org/ICEF/ICEF2020/volume/84034

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