Flow and combustion characteristics of an annular combustor

Abstract

Measurements of velocity, temperature, and species concentrations have been obtained in a gas turbine combustor comprising two rectangular sectors and for air-fuel ratios of 29 and 37. The primary vortex was driven by the air-flow through three film-cooling slots and was limited in its downstream extent by primary jets. Two further film-cooling slots and dilution holes controlled the exit flow properties. Natural gas was used as fuel and supplied through a T-vaporizer. Measurements were obtained with two arrangements. The first arrangement corresponded to the geometry of a small combustor used in helicopter engines and had its vaporizer exists in line with the primary holes which, in turn, were in line with the gaps between the dilution holes. The second arrangement was used to quantify the effect of moving the primary holes by 1 2 - pitch so that the primary and dilution holes were in line with each other but out of line with the vaporizer exits. The results showed that the position of the eye of the primary vortex varied in the cross-stream direction. In the gaps between the primary holes, it was located near the midplane of the combustor and moved toward the upper wall in regions close to the primary jets. The usual in-line arrangement of the primary holes with vaporizer exits resulted, therefore, in hot regions in the primary zone which were in line with vaporizer exits and positioned close to the upper wall. Moving the primary holes by 1 2 - pitch caused the downward movement of the hot regions in the primary zone and with this arrangement excess fuel was transported out of the primary zone along a path further from the center plane so that in the exit plane hot regions were located away from the vaporizer exists contrary to the usual arrangement where the general temperature pattern of the primary zone was maintained at the exit. The effect of airfuel ratio was found to be small in the primary zone and modest in the exit plane and the exit plane pattern factors were higher than those of engine practice mainly due to the atmospheric conditions of the present experiments. Results also showed that in the primary zone, reaction was controlled more by physical than chemical processes and that in the intermediate and dilution zone fuel breakdown and CO oxidation were chemical kinetic rate limited.