Direct fuelling of each shear layer generated by an array of holes in a grid plate was shown to have ultra-low NOx emissions combined with a good flame stability, compared with a premixed system. Two methods of fuel injection were investigated that had opposite NOx/stability characteristics. Four shear layers in a 76 mm combustor were used at gas turbine primary zone operating conditions with 60% simulated primary zone air at one bar pressure. The fuels used were propane and natural gas and a minimum NOx emission of 2.5 ppm at 15% oxygen, compatible with a 0.1% inefficiency, was demonstrated for natural gas with a reasonable stability margin. These designs have the potential for a dry NOx solution to any current or proposed gas turbine NOx regulation for natural gas.

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