Flammable mixtures of most fuels are normally burned at relatively high temperatures, which inherently results in the formation of substantial emissions of nitrogen oxides. In the case of gas turbine combustors, the formation of nitrogen oxides can be greatly reduced by limiting the residence time of the combustion products in the combustion zone. However, even under these circumstances, undesirable quantities of nitrogen oxides are nevertheless produced. Additionally, limiting such residence time makes it difficult to maintain stable combustion even after ignition. The present study relates to the design of gas turbine combustors for the reduction of nitrogen oxides emissions by heterogeneous catalysis. Steady-steady simulations are performed using computational fluid dynamics. The fluid viscosity, specific heat, and thermal conductivity are calculated from a mass fraction weighted average of species properties, and the specific heat of each species is calculated using a piecewise polynomial fit of temperature. Natural parameter continuation is performed by moving from one stationary solution to another. Particular emphasis is placed upon the sustained combustion of at least a portion of fuel under essentially adiabatic conditions at a rate which surmounts the mass transfer limitation. The results indicate that it is possible to achieve essentially adiabatic combustion in the presence of a catalyst at a reaction rate many times greater than the mass transfer limited rate. Flammable mixtures of carbonaceous fuels normally burn at relatively high temperatures, and substantial amounts of nitrogen oxides inevitably form if nitrogen is present. Complete catalytic combustion of a target species can only occur when oxygen gas is found in molar stoichiometric excess; a condition which is easily met when the target species is present in trace quantity in air. In combustion systems utilizing a catalyst, there is little or no nitrogen oxides formed in a system which burns the fuel at relatively low temperatures. In the mass transfer limited zone, the reaction rate cannot be increased by increasing the activity of the catalyst because catalytic activity is not determinative of the reaction rate. Among the unique advantages of the catalytically supported thermal combustion in the presence of a catalyst is the fact that mixtures of fuel and air which are too fuel-lean for ordinary thermal combustion can be burned efficiently.

Keywords: Heterogeneous catalysis; Nitrogen oxides; Gas turbines; Flammable mixtures; Thermodynamic properties; Combustion phenomena