Effect of Charge Preparation Strategy on HCCI Combustion.

HCCI;Combustion;Internal Combustion Engine;Stratification;CFD;Negative Valve Overlap;Mechanical Engineering;Engineering;Mechanical Engineering

Kodavasal, JanardhanLavoie, George A. ;

University of Michigan

关键词: HCCI;    Combustion;    Internal Combustion Engine;    Stratification;    CFD;    Negative Valve Overlap;    Mechanical Engineering;    Engineering;    Mechanical Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/99766/jankod_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

A critical factor determining Homogeneous Charge Compression Ignition (HCCI) combustion characteristics and emissions is preparation of the fuel-diluent charge prior to ignition. The choice of charge preparation strategy impacts diluent composition and stratification. Presently, there is a gap in fundamental understanding as to the impact of these strategies on charge distribution within the reaction space and consequent effects on HCCI combustion. In this doctoral work, fully-coupled CFD/chemical kinetics simulations are performed for various competing charge preparation strategies at a typical HCCI operating point to study the differences in burn duration and emissions arising from these strategies. The strategies studied are: air versus external EGR dilution, Negative Valve Overlap (NVO) versus Positive Valve Overlap (PVO) operation, and premixed fueling versus direct injection. The CFD reaction space is analyzed to determine the reactivity stratification prior to ignition arising from each of these strategies. A sequential CFD-multi-zone model is developed as a diagnostic tool wherein CFD simulation is performed over the gas exchange period until a transition point before TDC, after which the CFD reaction space is mapped onto a multi-zone chemical kinetic model. This tool is used to decouple various concurrent effects. For example, by selectively choosing to map thermal stratification from the CFD domain onto the multi-zone model while ignoring compositional stratification, the relative contributions of thermal and compositional stratification arising from NVO operation are isolated. Based on these insights from CFD, a standalone quasi-dimensional HCCI combustion model incorporating kinetics is built, featuring a computationally efficient methodology (developed as part of this work) to capture wall heat loss driven thermal stratification, as an alternative to expensive CFD simulation. It is shown that predictions from this model correspond well with results from detailed CFD/kinetics simulations over a range of operating conditions, for different engine geometries, while being up to two-orders of magnitude faster than CFD, making this model ideal for use in system-level codes.