Automatic Chemistry Mechanism Reduction of Hydrocarbon Fuels for HCCI Engines Based on DRGEP and PCA Methods with Error Control

Abstract

The chemical kinetics of hydrocarbon fuels determines the combustion characteristics and pollutant emissions of homogeneous charge compression ignition (HCCI) engines. Including comprehensive chemical mechanisms in HCCI engine models provides accurate predictive results that can be used to improve engine designs. However, a large number of simulations are usually required to optimize an HCCI engine, and the use of comprehensive chemical mechanisms is prohibitive. Furthermore, an increased demand for surrogate fuels that better represent real fuels has resulted in further increases in the size of chemical mechanisms as the carbon number of surrogate fuel species and the number of fuel components considered increases. Consequently, reduced mechanisms of smaller sizes, which are able to represent their corresponding comprehensive mechanisms over a wide range of conditions are necessary. This paper presents an approach that fully automates the process of reducing comprehensive chemical mechanisms of fuels for HCCI engines. The approach is based on the directed relation graph with error propagation (DRGEP) and principal component analysis (PCA) methods. In the first stage, the DRGEP method is used to efficiently remove redundant species. This is followed by the use of the PCA method to further remove insignificant reactions and species. During the entire process, the performance of the reduced mechanism is monitored to ensure that the generated mechanism satisfies user-specified error tolerances. In the present study three comprehensive mechanisms that include n-heptane, iso-octane, and methyl decanoate (MD) were investigated. The proposed approach successfully reduced the comprehensive mechanisms of n-heptane (561 species and 2539 reactions), iso-octane (857 species and 3606 reactions), and MD (2878 species and 8555 reactions) to reduced mechanisms with sizes of 140 species and 491 reactions, 195 species and 647 reactions, and 435 species and 1098 reactions, respectively, while maintaining small errors compared to the full mechanisms.

A reduced toluene reference fuel chemical kinetic mechanism for combustion and polycyclic-aromatic hydrocarbon predictions

“…Direct Relation Graph with Error Propagation (DRGEP) [39,40], reaction pathway, rate of production and sensitivity analyses were applied for the mechanism reduction. The mechanism reduction starts with the DRGEP method to remove unimportant species and reactions from the base mechanism to obtain an intermediate mechanism; then reaction pathway, rate of production and sensitivity analyses were applied to identify the most important species and reactions.…”

Reduced Mechanism Approach of Modeling Premixed Propane-Air Mixture Using ANSYS Fluent

“…Transport effects are neglected while performing the reduction, but their influence is, nonetheless, and often checked a posteriori by testing the full and reduced mechanisms on a simplified model that includes these effects. A comprehensive review of reduction techniques for kinetic models with an emphasis on combustion can be found in [8], [9], [10], [11] and [12].…”

3D CFD simulation of a natural gas fueled HCCI engine with employing a reduced mechanism

“…Furthermore, since combustion occurs as a result of the interaction of the chemical processes with in-cylinder thermal conditions, combustion timing control is difficult [5]. http In this way, understanding fuel chemistry as well as producing a comprehensive model that appropriately describes combustion process is critically important for HCCI engine design and optimization [6]. Natural Gas (NG) is an attractive alternative to conventional fossil fuels because of the booming shale gas production in the US and is one of effective ways to reduce the CO 2 emissions due to its low carbon contents [6].…”