Reduction of Nitrogen Oxide Emissions From a Gas Turbine Combustor by Fuel Modifications

Abstract

A broad experimental program was undertaken to assess the feasibility of reducing NOx from aircraft gas turbine engines by fuel modifications (additives and/or treatments). The modifications were selected without regard to practical limitations in order not to obscure potentially useful approaches. The Esso high pressure cannular combustor was used to simulate the characteristic emissions of gas turbines. Approximately 70 fuel modifications were tested using Jet A as the base fuel. These fell into 7 general categories: (a) soluble organometallic additives which become heterogeneous reduction or decomposition catalysts, (b) additives that scavenge or recombine oxygen atoms, (c) additives that reduce peak temperatures, (d) additives that delay ignition, (e) additives that change spray fluid-dynamics, (f) additives that decompose NO or inhibit the NO producing chain reactions, (g) combinations of the foregoing for synergistic effects. Only category a proved to be effective in reducing NOx emissions. Transition metals added to the Jet A fuel as organometallic compounds reduced NOx by as much as 30 percent. Other additives, some not containing metals, reduced NOx by up to 15 percent. None of the investigated additives was fully acceptable because of the relatively low NOx reduction that was obtained even with high additive treat rates. The experimental work was carried out at an overall air to fuel ratio of around 50 and at a pressure of 48 psig. The exhaust gas composition was typical of the latest aircraft turbine engines with the exception of the carbon monoxide levels which were too high. A statistical analysis of results with unmodified Jet A fuel indicated that variation of air inlet moisture from 0.00025 to 0.0025 lb of water per lb of air, and pressure variations between 45 and 60 psig had an insignificant effect on NOx production over the range of the experimental work.