Experimental analysis on micro diffusion flames formed by oxygen combustion of H2-CO2 mixture using counterflow burners

Abstract

Microscale hydrogen (H2) combustion is one of the promising technologies for renewable miniaturized heat sources. This study analyzes the oxygen combustion of H2 in small-scale counterflow burners, with carbon dioxide (CO2) added for safe hydrogen treatment (flame visualization and reduction of flame propagation velocity). The effects of burner inner diameter, burner gap, and gas flow rate on the flame shape/size (thickness and diameter) are measured through flame image analysis. The experimental results show that the flame thickness and diameter monotonically decrease with a decrease in the burner inner diameter, burner gap, and H2 flow rate. The flame thickness decreases with an increase in the flame stretch rate, and the approximate curve representing this relationship varies depending on the burner inner diameter and H2 flow rate. Accordingly, the flame thickness normalized by H2 flow velocity and burner inner diameter is newly proposed, which strongly correlates with the flame stretch rate and converges on a single line, i.e., inverse of the square root of the flame stretch rate. These findings are also applicable to biogas (CH4-CO2 mixture)-O2 micro counterflow diffusion flames with the same CO2 concentration in the fuel gas and apparent equivalence ratio.

Keywords

• hydrogen combustion
• oxygen-enriched combustion
• micro diffusion flame
• counterflow burner
• carbon-dioxide addition
• flame stretch rate
• biogas