Over the past three years, Solar Turbines International, an Operating Group of International Harvester, has been engaged in characterizing the NOx emissions and operation of two particular types of lean, premixed combustors, namely the Jet Induced Circulation (JIC) and Vortex Air Blast (VAB) configurations and was concerned primarily with the NOx emissions at a simulated high-altitude, supersonic cruise condition. The VAB combustor demonstrated the capability of meeting the NOx goal of 1.0 g NO2/kg fuel at the cruise condition (Tin = 833 K, Pin = 5 atm, Tout = 1778 K). In addition, the program served to demonstrate the limited low-emissions range available from the lean, premixed combustor. A follow-on effort, the results of which form the basis of this paper, was concerned with the problem of operating these lean, premixed combustors with acceptable emissions at simulated engine idle conditions. Various techniques have been demonstrated that allow satisfactory operation on both the JIC and VAB combustors at idle (Tin = 422 K, Pin = 3 atm, Tout = 917 K) with CO emissions below 20 g/kg fuel. These include degrees of variable geometry, fuel switching and fuel-staging designs. The VAB combustor was limited by flashback/autoignition phenomena at the cruise conditions to a pressure of 8 atm. The JIC combustor was operated up to the full design cruise pressure of 14 atm without encountering an autoignition limitation, although the NOx levels, in the 2 to 3 g NO2/kg fuel range, exceeded the program goal.

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