Simultaneous measurement of carbon monoxide and carbon dioxide for combustion diagnosis using 2 μm laser absorption spectroscopy

Carbon monoxide (CO) and carbon dioxide (CO₂) are products of incomplete combustion and complete combustion, respectively. Time-resolved knowledge of CO and CO₂ exhaust concentrations will aid in improving combustion strategies, control, and efficiency. To achieve online high-precision simultaneous measurement of CO and CO₂, a tunable diode laser absorption spectroscopy-based sensor is designed and constructed. Two diode lasers with central wavelengths of 2.3 and 2.0 μm are multiplexed in time-division to cover the absorption spectral lines of CO at 4285.00 cm⁻¹ and CO₂ at 4989.96 cm⁻¹, respectively. Wavelength modulation spectroscopy with second harmonic detection normalized by the first harmonic (WMS-2f/1f) is employed. A software lock-in amplifier and inversion algorithm are implemented for data processing and concentration acquisition. The entire measurement system is based on the idea of a virtual instrument and is carried out using a high-speed data acquisition card and a computer. Experimental verification demonstrates that the measurement accuracies of CO and CO₂ were 2.47% and 2.56%, respectively, with a time resolution of 20 ms. Dynamic measurement experiments with an alcohol blast burner validate the feasibility of measuring CO and CO₂ in actual combustion environments. The developed sensor demonstrates the potential for real-time and in situ carbon emission measurement for combustion diagnosis.