STUDIES OF LEAN BLOWOUT IN A STEP SWIRL COMBUSTOR

The design requirements of a modem gas turbine combustor are increasin gly dictated by wide stability limits, short flame length, and uniform mixing. To achieve the best trade-off between these three factors, fl ame characteristics (length, shape, mixedness), lean blowout (LBO), an d optimum combustor configuration should be investigated over a wide r ange of inner and outer air velocities, inner and outer vane angles, a nd co- versus counterswirl arrangements. Such an investigation was per formed in a step swirl combustor (SSC) designed to simulate the fuel-a ir mixing pattern in a gas turbine combustor dome fitted with an airbl ast atomizer. It was found that an increase in the outer vane angle an d a decrease in inner air velocity decreased the flame length. LBO was improved when outer flow swirl intensity was increased. An optimum ha rdware and velocity configuration for the SSC was found for inner swir l = 45 deg, outer swirl = 60 deg, coswirl direction, and inner air vel ocity = outer air velocity = 16 m/s. This optimum SSC configuration yi elded: (i) low values of LBO, (ii) short flame length, (iii) uniformly mixed stable flame, and (iv) little or no variation in these characte ristics over the range of operation of SSC. Finally, the co- versus co unterswirl an arrangements and the operation of the optimized combusto r configuration are discussed.