Development of Detailed Kinetic Mechanism to Study Low Temperature Ignition Phenomenon of Kerosene

Abstract

The objective of this work is to develop a detailed kinetic mechanism for low temperature kerosene oxidation, which is essential to predict premature auto-ignition of liquid fuels in gas turbines and cool flame behavior in hydrocarbon reformers for fuel cells. Kerosene, a fractional distillate of petroleum known by its generic term, is comprised of a wide range of aviation fuel grades such as Jet A, Jet-4, JP-8 etc, with a chemical composition varying from higher order n-alkanes to complex aromatics. Thus, developing a detailed kinetic mechanism to represent actual kerosene is not only cumbersome but also computationally intensive to implement. Therefore, very often a surrogate mixture with known chemical composition is devised to study kerosene oxidation. In this work, a hierarchical structure of the kerosene mechanism with approximately 1400 reactions of 550 species is developed using a surrogate mixture of n-decane, n-propylcyclohexane and n-propylbenzene to represent major components of kerosene, namely n-alkanes, cyclo-alkanes and aromatics, respectively. Since a major portion of the kerosene consists of very reactive n-alkanes rather than the less reactive ring structures, the low temperature oxidation kinetics is predominantly dictated by n-alkanes. Thus, the modeling effort is mainly focused on developing a low temperature mechanism for n-decane. The low-temperature oxidation of the individual fuel of the surrogate mixture, especially n-decane, was fairly well-characterized experimentally in shock-tubes and flow-reactors, and hence, the mechanism is validated against the available experimental measurements. With the objective of achieving a more comprehensive mechanism, the model validation is extended to include target data for wide range of conditions including high pressure and high temperature experimental data available in the literature. The model predictions of the kerosene mechanism were compared to the available experimental data on ignition delay time as well as the reactivity species profiles of different aviation grade fuels obtained in flow reactors. The predictions of the kerosene mechanism agree with the experimental data fairly well especially at low to intermediate temperature regimes. A sensitivity analysis was performed to identify the rate-limiting steps at low, intermediate and high temperatures. It was observed that reactions involving ketohydroperoxides and hydrogen-peroxides are the most important reactions at low and intermediate temperatures, respectively.