H2 enrichment impact on the chemiluminescence of biogas/air premixed flames

A numerical and experimental study of chemiluminescent signals of OH*, CH*, C-2* and CO2* is conducted for hydrogen enriched CH4/CO2/air premixed laminar flames. Biogas blends (CH4/CO2) with 0 <= chi(CO2) <= 30% are enriched in the range 0 <= chi(H2) <= 10% and burned under lean conditions (0.82 <= phi <= 1) in a Bunsen burner. Light is captured by a spectrometer and the intensity of chemiluminescent radicals is calculated by subtracting a background emission from the intensity at predefined wavelengths. Flame pictures are also taken and post-processed to calculate flame area. The simulations are conducted in Cantera using a freely propagating flame routine coupled with the GRI-Mech 3.0 mechanism, without the nitrogen kinetics. The impact of hydrogen enrichment in light emission through thermal-diffusion, concentration and chemistry/kinetics effects is studied numerically using False argon and False hydrogen. Intensity ratios, in particular OH*/CH/ and CO2*/CH*, display linear trends with hydrogen concentration. OH*/CH*, OH*/C-2, CH*/C-2* and CO2*/CH* are used to estimate the equivalence ratio (phi) in hydrogen enriched biogas flames. An exponential function is proposed to model the behavior of both numerical and experimental curves. OH*/CH* displays the best results with great agreement with simulations. OH*/C-2*, CH*/C-2* and CO2*/CH* are able to infer phi with proper calibration. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.