Evidence Supporting a Simplified Approach to Modeling High-Temperature Combustion Chemistry

摘要

Real fuels may contain thousands of hydrocarbon components. This paper examines how nature simplifies the problem. We will discuss the internal structure of the fuel oxidation process at high temperatures. Over a wide range of conditions, large hydrocarbon molecules undergo thermal decomposition to form a small set of low-molecular weight fragments, and in the case of conventional petroleum-derived fuels, the composition variation in the decomposition products is reduced by the law of large numbers. From a joint consideration of elemental conservation, thermodynamics and chemical kinetics, it will be shown also that the composition of the thermal decomposition products is a weak function of the thermodynamic condition, the fuel-oxidizer composition and fuel composition within the range of temperatures of direct relevance to flames and high temperature ignition. Based on these findings, we explore a hybrid chemistry (HyChem) approach to modeling high-temperature oxidation of real fuels: the kinetics of thermal or oxidative thermal decomposition of the fuel is lumped using kinetic parameters derived from experiments, while the oxidation of the decomposed fragments is described by a detailed reaction model. Sample results will be given that supports this modeling approach.