Modeling of PCCI combustion with FGM tabulated chemistry

Premixed Charge Compression Ignition (PCCI) is a new combustion concept aiming a simultaneous reduction of oxides of nitrogen and soot emissions. Therefore the operation focuses on improved fuel-air mixing before ignition and lower maximum in-cylinder temperatures during the complete engine cycle. In the PCCI-regime, the injection and ignition events do not overlap due to the longer ignition delay timings. As such ignition is not influenced by the injection event like in the conventional operation and it is essentially governed by chemical kinetics. Numerical methods should incorporate flow and chemistry models in an accurate way. However, the computational demand for modeling these phenomena is high and the researchers work on several reduction techniques to achieve a practical computational efficiency. In this work the Flamelet Generated Manifold method is applied within the Computational Fluid Dynamics (CFD) framework to study PCCI combustion. In FGM, thermo-chemical properties are preprocessed by solving canonical systems (here, Igniting Counter-flow Diffusion Flamelets and Homogeneous Reactors) and stored in a manifold as a function of controlling variables. Since ignition control is difficult in the aforementioned combustion concept, the accurate prediction of ignition phenomena is significant. Simulations are performed with three different mesh settings, where the course grid proves to be sufficiently accurate. Later the effect of multiple pressure levels is investigated using both canonical systems and the study shows that a number of three pressure levels is sufficient to capture the ignition phasing with Homogeneous Reactors based FGM tables. Finally, the sensitivity of ignition with respect to injection timing is shown to be predicted precisely. (C) 2013 Elsevier Ltd. All rights reserved.