Measurement of CO temperature and concentration in flat flame based on mid infrared wavelength modulation

Abstract

CO in combustion products of aeroengine is a sign product of incomplete combustion. Real-time monitoring of CO can feedback combustion efficiency, which is of great significance to the design of combustion chamber and the optimization of fuel ratio of aeroengine. In this paper, based on the mid infrared absorption spectroscopy, a single optical path calibration-free wavelength modulation method is proposed to measure the temperature and concentration of CO in a flat flame. Firstly, the spectrum of light intensity signal and the amplitude frequency response of different frequencies are analysed, and the appropriate scanning frequency and modulation frequency are selected. Secondly, the equalization of Butterworth filter in DPLA is proposed to extract the first and second harmonics. The filter can effectively reduce the influence of nonlinear phase. Furthermore, calibration-free wavelength modulation method is simulated to measure CO at different temperature and concentration. Finally, CO in flat flame with different equivalence ratio at 5mm was measured for verification. The relative error between the measurement results of calibration-free wavelength modulation and that of thermocouple measurement is within 3.6% in the range of concentration 0.11% ∼ 0.24%, which verified the feasibility and effectiveness of the measurement scheme, and provided a reference for the CO concentration measurement at the outlet of aeroengine.