Development of a reduced mechanism for n-heptane fuel in HCCI engines

Abstract

Due to the lack of direct control of combustion timing in the homogeneous charge compression ignition engines, the chemistry of the in-cylinder charge is responsible for the ignition. Thus, obtaining knowledge about fuel chemistry has a significant importance in engine design and optimization. Large numbers of detailed chemical kinetics mechanisms have been suggested to predict various fuels oxidation. However, employing comprehensive chemical kinetics mechanisms in predictive models results in the high demand for simulation time which makes the use of these mechanisms questionable. Consequently, reduced mechanisms of smaller sizes are needed. The objective of this study is to produce reduced mechanism of n-heptane fuel, to be applicable for CFD simulation, by utilizing a two-stage reduction process. This work is performed by using a validated single zone combustion model. To remove unimportant species at the first stage, the directed relation graph with error propagation (DRGEP) is applied. In the second stage, the principal component analysis (PCA) method is used to eliminate insignificant reactions and species. Peak pressure, maximum heat release, and CA50 have been selected as representative parameters for the performance of engine. For the generated reduced mechanism at each reduction step, these parameters would be calculated, and the deviations from the corresponding value obtained by applying detailed mechanism to the model will be evaluated until user-specified error tolerances violate. This combination of two methods successfully reduced the detailed Golovichev’s n-heptane mechanism (57 species and 290 reactions) to a reduced mechanism with size of 40 species and 95 reactions, while maintaining small errors (less than 1 present) compared to the detailed mechanism.