The influence of air distribution on homogeneity and pollutant formation in the primary zone of a tubular combustor

This paper summarizes the work undertaken by the Defense Research Agency (DRA Pyestock) for the BRITE/EURAM Low Emissions Combustor Technology Project No 1019. The work was jointly funded by the CEC (DGXIIH), the UK DTI (CARAD - ATF4) and the UK MOD (DCSA). The gas turbine emissions problem is summarized and the design philosophy of the experimental program is described. The principal objective was to demonstrate a simultaneous reduction of NO(x) and smoke emissions together with acceptable idling emissions and stability in an unstaged combustor. A secondary objective was to demonstrate the extent to which NO(x) and smoke could be reduced if the combustor was to be used as the main stage of a staged combustor where a poorer idling performance could be accepted. The work consisted of a parametric investigation of the principal factors controlling the emissions produced in the combustor primary zone. Particular emphasis was placed on the influence of the distribution, number, and size of air entry holes and of residence time on pollutant formation. The results from the complete experimental program are summarized. These suggest that NO(x) reductions of about 30-40 percent should be possible together with excellent smoke and idling performance. The results suggest that NO(x) was formed very close to stoichiometric flame temperatures even at very weak combustor mixture strengths and under well mixed conditions. The reductions that were achieved were largely as a result of reductions of residence time.