Low-temperature Combustion - Automatic-generation of Primary Oxidation Reactions and Lumping Procedures

The aim of this paper is to present some general rules for the automatic generation of primary oxidation reactions of large hydrocarbon fuels. The proposed approach is applied to n-paraffins for reason of simplicity. Nevertheless, the final goal is to feed the tested rules and kinetic parameters into a more general and effective expert system for the generation of primary mechanisms of real mixtures containing heavier branched hydrocarbons. The first step is the classification of the primary reactions involved in low-temperature oxidation, together with the definition of a limited set of their intrinsic kinetic parameters. These independent rate constants are validated on the basis of primary experimental measurements of pyrolysis and oxidation. In addition to this, the paper analyzes some useful simplifications for the kinetic modeling of secondary combustion processes. As the carbon number of the hydrocarbon fuel rises, the detailed reaction schemes become very complex. The number of isomers of the same homologous class of molecules and radicals increases and the number of reactions increases simultaneously. In these cases, the automatic generation of the primary oxidation reactions and properly conceived lumping procedures, both for reactions and components, become very useful. These lumped mechanisms of heavy species consist of a limited number of equivalent reactions. Then, this small subset of equivalent reactions has to be coupled with a very detailed scheme for the oxidation of C-1-C-4 species. The final result is still a very large number of reactions, which makes it incompatible with c.f.d. calculations, but whose extension to heavier species becomes easier to handle. A few comparisons of experimental and predicted results for the low-temperature oxidation of n-butane and n-pentane illustrate the applicability of this approach.