A versatile coupled progress variable/REDIM model for auto-ignition and combustion

In this work, we present a reduced model for treating chemical reactions in combustion simulations, with special attention on combustion in IC engines. The model which is based on low-dimensional manifolds in state space, is able to describe auto-ignition, burning in quasi homogeneous media as well as chemical reactions which are strongly coupled with molecular transport, like, e.g., in flame propagation. A coupling scheme is developed for existing concepts for reduced treatment of combustion, namely a progress variable model (PVM) and the reaction-diffusion manifold approach (REDIM). We discuss a simple, robust method for this coupling, based on an additional variable, namely the normalized strength of molecular transport. The implementation and behavior of the resulting coupled model are shown. To demonstrate the performance of the model, numerical simulations of representative combustion scenarios are performed, both with fully detailed calculations and with the reduced model. The comparison of results obtained with detailed and reduced computation shows that the strongly reduced model, which requires only five independent variables in total, still can accurately predict a wide range of combustion-relevant scenarios.