Comparison and Parametric Study of Flameless Oxidation in a Gas Turbine Using Two Kinetics Mechanisms

Abstract

The so-called "Flameless Oxidation" is a novel combustion mode, in which combustion products are re-circulated and mixed into the fresh incoming fuel and air streams. This reduces the concentration of the reactants and thereby reducing the reaction rate through avoiding the formation of sharp high temperature zones in the combustion chamber. Flameless combustion has been acknowledged as one of the most interesting combustion technologies to meet both the targets of high energy efficiency and low pollutant emissions. This technology has already been successfully applied and exploited in industrial burners. The present investigation is concerned with the application of the flameless combustion mode to an adiabatic combustor, typically used in gas turbine engines. Detailed chemical kinetics calculations, by means of a specific zero-dimensional loop reactor model, have been performed to analyze its chemical aspects. The model simulates the combustor by a number of reactors that represent different zones in the combustion chamber. The main objective of this study is to increase the understanding of NOx formation from flameless mode, where currently very few experimental data are available. The investigation is focused on a comparison of the influence of pressure, residence time and temperature on the NO_x and CO emissions, using two reaction mechanisms of the C/H/O/N system: the Miller-Bowman mechanism and the GRI_MECH3.0 mechanism. Simulation results clearly illustrate that even at high operating temperatures and pressures, NOx emissions could be reduced by flameless combustion to very low levels. A comparison between the predictions obtained by using the two chemical kinetics mechanisms is presented and discussed. It is shown that the predictions of the Miller-Bowman mechanism deviate from the predictions of the GRI3.0 mechanism in many aspects, especially as related to NOx emission results.