Experimental and numerical investigation of stability and emissions of hydrogen-assisted oxy-methane flames in a multi-hole model gas-turbine burner

Abstract

This paper reports experimental and numerical study of stability and combustion characteristics of premixed oxy-methane flames with hydrogen-enrichment (CH4–H2/O2–CO2 flames) in a model multi-hole burner for clean energy production in gas turbines. The combustor lean blow-out (LBO) limit was presented on an equivalence ratio (Ø) - hydrogen fraction (HF: volumetric fraction of H2 in a mixture of H2+CH4) map spanning over Ø-values of 0.1–1 and HF-values of 0–70% at fixed hole jet velocity and oxygen fraction (OF: volumetric fraction of O2 in a mixture of O2+CO2) of 5.2 m/s and 30%, respectively. The condition of the combustion chamber is assumed to be depicted by the corrugated premixed flame regime. The premixed turbulent flame was modeled using the reaction progress variable flame front topology approach with the Large Eddy Simulation (LES) technique. The recorded combustor stability maps showed great resistance of the micromixer burner technology to flashback, recommending its use for stable gas turbine operation. The results show that H2-enrichment widens the combustor operability limits (higher turndown ratio) by extending the LBO from Ø = 0.45 at HF = 0% down to Ø = 0.15 at HF = 70% with a slight reduction in the heat release factor by 0.1. The high reactivity and higher flame speed of H2 ensures the sustenance of flame at lower equivalence ratios. At high equivalence ratios, H2 addition enhances the reaction rates and makes both the primary and secondary reaction zones shorter and more intense. Increasing HF leads to increase in the Damköhler number (Da) and decrease in both the Karlovitz number (Ka) and flame thickness. The CO emission at the combustor outlet reduced significantly from 241 ppm at HF = 0% to 33.1 ppm at HF = 10%, then it increased back to 364 ppm at HF = 50%.