Closed-loop equivalence ratio control of premixed combustors using spectrally resolved chemiluminescence measurements

A control system based on a multiwavelength chemiluminescence sensor has been developed and tested to adjust the operating point of an optically accessible, lean premixed methane/air burner operated under pressures up to 20 bar and equivalence ratios ranging from 0.5 to 1.2, as typically found in premixed gas turbine combustors. The sensor comprises a broadband, low-resolution grating spectrometer scanning the light emitted by the burner in the range 250-850 run. Spectral distributions are analyzed in real time to determine the equivalence ratio according to a novel method described in this paper. Radical emission data in the form of intensity ratios OH*/CH* and CO2*/CH* are first measured during an off-line combustor identification step carried out with the same monochromator. These data are collected in a lookup table, which is then used to monitor the equivalence ratio and control the fuel mass flow rate. Closed-loop control using this chemiluminescence sensor has been tested over a broad range of operating conditions. The performance of the sensor and control system is assessed by simulating changes in fuel quality and by operating the system with contaminated windows. Equivalence ratio control was successfully achieved under all of these conditions, showing that a suitable processing of multiwavelength data allows premixed gas turbine combustion control.