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A Zero-Dimensional Phenomenological Model for RCCI Combustion Using Reaction Kinetics
Abstract:
Homogeneous low temperature combustion is believed to be a promising approach to resolve the conflict of goals between high efficiency and low exhaust emissions. Disadvantageously for this kind of combustion, the whole process depends on chemical kinetics and thus is hard to control. Reactivity controlled combustion can help to overcome this difficulty. In the so-called RCCI (reactivity controlled compression ignition) combustion concept a small amount of pilot diesel that is injected directly into the combustion chamber ignites a highly diluted gasoline-air mixture. As the gasoline does not ignite without the diesel, the pilot injection timing and the ratio between diesel and gasoline can be used to control the combustion process.
A phenomenological multi-zone model to predict RCCI combustion has been developed and validated against experimental and 3D-CFD data. The model captures the main physics governing ignition and combustion. The direct diesel injection is modeled using Hiroyasu's packet approach, where all packets are treated as thermodynamic zones. After the end of injection, mixture formation is modeled as a process dominated by turbulent mixing with mass transfer from zone to zone. Therefore, an algebraic turbulence model has been implemented and compared to 3D-CFD turbulence data. As RCCI combustion is kinetically controlled, heat release is solely modeled using reaction kinetics. To account for chemical reactions a reduced mechanism is used and each zone is considered as a constant volume reactor.