Biogas combustion: Chemiluminescence fingerprint

A numerical and experimental study was conducted, with the purpose of inferring the influence of the CO2 concentration (xCO2) for different equivalence ratios (ϕ) on CH4/CO2/air (biogas) flames chemiluminescence. A thorough analysis on the signals of OH∗, CH∗, C2∗ and CO2∗ was performed. Typical biogas compositions were tested under laminar atmospheric flame conditions, within the unburned equivalence ratio of 0.9 and 1.14 with CO2 concentrations up to 40% in the blend. Experimental measurements of chemiluminescence were done using spectroscopy in the UV-visible region of the spectra. Simulations were performed with the GRI-Mech 3.0 mechanism without accounting for the nitrogen chemistry, extended with a chemiluminescence kinetics of OH∗, CH∗, C2∗ and CO2∗, in a burner-stabilized frame in CANTERA. Experimental measurements and numerical simulations are compared and generally are in good agreement. It was verified that CO2 dilution leads to a regular decrease in the emission intensities of OH∗, CH∗, C2∗ and CO2∗. Relations between chemiluminescence intensity ratios and xCO2 and ϕ were found. It was shown that OH∗/CO2∗ and C2∗/CO2∗ have the potential predict xCO2 in CH4/CO2/air flames. Moreover, it was verified that OH∗/CH∗, OH∗/C2∗ and CH∗/C2∗ are well suited to infer ϕ for the blends tested. It was verified that xCO2 does not cause relevant changes in the chemiluminescence ratios when inferring ϕ.