State-of-the-art gas turbines engines continuously strive for higher cycle efficiencies and lower pollutant emissions. The gas turbine combustor is critical for achieving these goals, and operation near the lean extinction limit is necessary. Slight changes in the flow splits (fuel and/or air) can lead to unexpected flame extinction, or other operational issues such as combustion oscillations. Operating these gas turbine combustors near the flame extinction limit could be improved if acceptable in-situ sensors for the combustion section were commercially available. Although exhaust gas oxygen sensors are commonly used in other combustion processes including large utility boilers and automobiles, the use of in-situ oxygen sensors in gas turbine engines has been limited. This paper will describe the results from rig tests in a pressurized lean premixed combustor. The O2 sensor technology used in these tests is commercially available for industrial boiler applications which typically operate near atmospheric pressure and oxygen levels that range from 0–3% of the effluent. In modern gas turbines, however, the amount of excess oxygen is considerably higher. These high levels of excess oxygen result in low level signals from the O2 sensor, which creates concern for in-situ monitoring in gas turbines. The results indicate that this sensor technology will operate at elevated pressure and at high levels of excess oxygen in the process gas suggesting possible application as an operational and diagnostic tool. Data will be presented to show the effects of different operating variables such as pressure, inlet-air temperature, heat-release, and fuel-air ratio.
Flame Structure of Lean Premixed and Diffusion Combined Flames near Extinction Limit