Combustion Timing Modeling and Control Framework for Biodiesel/Diesel Blends During Pre-Mixed Combustion

Strict emissions constraints and interest in increasing engine efficiency are causing growing attention on advanced combustion strategies such as premixed charge compression ignition (PCCI) which can drastically lower particulate matter, and nitrogen oxide emissions. Control of PCCI requires an understanding of the underlying dynamics that govern the combustion process and can be challenging since there is no direct trigger for beginning the combustion process. In addition, the timing of the actual start of combustion (SOC) is affected by the in-cylinder conditions (such as temperature and pressure) as well as the fuel being utilized. This paper focuses on the development of a control-oriented physics-based model which predicts the SOC for diesel and biodiesel to within ±2°CA. Validation efforts demonstrate the effectiveness of the model in capturing SOC for multiple fuels and point to the strong role of in-cylinder oxygen content in influencing the SOC. A control framework which controls SOC through regulation of in-cylinder conditions is shown to be effective in controlling combustion phasing for both diesel and biodiesel in PCCI.