Generalized Entropy Production Algorithm for onthe- fly reduction of detailed mechanisms in CFD codes

To widen the adoption of renewable fuels, new combustor designs, often working in new combustion regimes, are required. The Computational Fluid Dynamics (CFD) approach is a well-established methodology to help in the design of combustion systems, but to deal with the detailed mechanisms required for accurate predictions of the new fuels is very challenging, because of the huge computational effort required. Current CFD codes adopt several algorithms to reduce significantly this effort. The chain of steps adopted in the reactingFoam application distributed with the open- source code OpenFOAM is an excellent example [1]: first, the ISAT method is applied to avoid re-computation of the kinetic evolution starting from states of the reactive mixture close to already computed states. To further reduce the required effort, without losing the generality of a detailed mechanism, an on-the-fly reduction of the kinetic mechanism is performed when a new starting state is detected that cannot be evolved from previous states. The advantage expected is that, having the new reduced mechanism be valid only for a single state, it can be much smaller than an a-priori reduced mechanism to be applied for every state, with computational benefits also on the stiffness of the resulting ODE to solve. The authors proposed a new algorithm for the full automatic generation of reduced chemical mechanisms [2]. It showed the advantages of an efficient detection of the main reactions, leading to small skeletal mechanisms and without any need of knowledge of the starting species. Therefore, this algorithm appears a good candidate for an on-the-fly reduction procedure in a CFD code. The results of such an implementation in the OpenFOAM code, alongside the discussion of the performance obtained in comparison with the methods already available in the public distribution of the code, will be the object of the presentation.