Modeling the combustion of high molecular weight fuels by a functional group approach

Modeling the combustion behavior of real fuels is a challenging task: Significant analytical efforts are required to characterize the fuel composition, and comprehensive kinetic models are necessary to reproduce the behavior of the different fuel components. Both these aspects become increasingly critical for fuels having a high molecular weight, wherein both the characterization of the single components and the kinetics involved in their oxidation become extremely complex. Indeed, kinetic models for large hydrocarbons can include thousands of species and tens of thousands of reactions. For these reasons, only a limited number of representative components are generally included in the simulations and these large kinetic mechanisms are reduced to simulate the behavior of real fuels in practical conditions. We propose a novel approach to the simulation of the combustion of high molecular weight fuels, wherein the fuel surrogate is defined in terms of pseudospecies including the functional groups contained in the actual fuel. These pseudocomponents, representing linear, branched, aromatic, saturated, and unsaturated structures, can undergo the typical reactions responsible for the low-temperature ignition of hydrocarbon as well as the interactions occurring in fuel blends. The basics of this concept will be presented, through application to linear and branched alkanes, and the potential of this approach is assessed by means of comparisons with experimental data and detailed kinetic simulations. The potential of this methodology for reducing computational expense in computational fluid dynamics simulations is also highlighted.