Numerical investigation of multiphase reactive processes using flamelet generated manifold approach and extended coherent flame combustion model

Abstract

For the calculation of multiphase reactive processes in computational fluid dynamics (CFD), detailed chemical kinetics and simplified combustion models are commonly applied. An appropriate modelling approach to overcome the high computational demand of chemical kinetics is the flamelet generated manifold (FGM), which prescribe the calculation of chemical kinetics in preprocessor for the generation of the look-up databases that are used during CFD simulations with interpolation procedure. For the calculation of the chemistry kinetics in processor, combustion models are commonly applied, such as Three-zones extended coherent flame model (ECFM-3Z) that features calculation of flame speed in turbulent conditions. The primary goal of the research is to investigate and validate FGM and ECFM-3Z models on the multiphase reactive process inside a compression ignition engine for single and multiple injection strategies. Additionally, an overview of the modelling methodology and capability of FGM and ECFM-3Z models is presented, where the impact of their features is analysed on the results inside a compression ignition engine. For the numerical simulations, CFD code AVL FIRE™ was used, where the calculated results such as in-cylinder pressure, temperature, rate of heat release, and nitric oxide emissions are computed. The FGM modelling approach showed higher ignition delay compared to the ECFM-3Z model for single-injection strategy, which can be attributed to the pretabulated autoignition conditions in three zones of the ECFM-3Z model. For the multi-injection strategy, such an ignition delay difference between FGM and ECFM-3Z is not observed since the small amount of injected fuel in pilot injections tends to have quicker ignition, which then creates better conditions for combustion of the more significant amount of injected fuel in the main injection. The experimental nitric oxide emission trend is achieved with both combustion modelling approaches, where the CFD calculation time for cases with FGM is reduced approximately by half. In comparison against the experimental values, both FGM and ECFM-3Z combustion modelling approaches showed the capability of predicting the influence of fuel injection strategy on the combustion process in passenger car compression ignition engines.