Experimental Investigation of No_x Emission in a Combustor with One and Two Sequential Combustion Stages

This article is the first of a cycle dedicated to the experimental investigation and process optimization of the combustion of an air-fuel mixture with gas temperatures at exit from the combustion chamber of approximately 1700 °C, while satisfying the requirements relating to emissions. The article is divided into two stages. The first stage examines the possibilities of obtaining minimal NO_x and CO concentrations when using a traditional (single-stage) system for combustion of a prepared air-fuel mixture (AFM). It presupposes the presence of one burner unit (BU) through which fuel and air enter the combustor (COMB), and the combustion process is executed in flame stabilization zones that are formed in it due to swirl generators and/or bluff bodies. For such a system, the effect on NO_x and CO emissions over the range of exhaust temperatures from 1300 to 1700°C (CC excess air coefficient from 2.2 to 1.6) from the following was studied: the quality of preparation of the AFM, the pilot burner air, the flow speed in the COMB, and the air temperature at intake. The second stage examined the possibility of reducing harmful emissions due to the use of a two-stage sequential plan of fuel combustion. This presupposes the presence of two BUs, one of which, a traditional one (BU1), is placed at the inlet face of the COMB; and a second, sequential one (BU2), on the side walls of the COMB below the flow. Here, results are produced in testing BU2, in the form of an annular sudden flow constrictor with fuel-injection apertures arranged on its circumference. The total fuel flow is partitioned between the stages. In the first stage, combustion occurs for fuel in the form of the AFM, and in the second the remaining fuel is combusted in the hot flow of gases of the first stage, depleted by oxygen. The effect of the AFM temperature intake to the first stage and the speeds of its feed to the COMB on NO_x and CO emissions over the range of exhaust temperatures from 1300 to 1700°C is studied for this system. The results were obtained in tests on a model CC at a test station of JSC VTI. Multivariate parametric studies on this subject were published earlier [1–3].