Effect of burner diameter and diluents on the extinction strain rate of syngas-air non-premixed Tsuji-type flames

Abstract

The present study focuses on the experimental determination of the global extinction strain rate (ag) for different syngas-air combinations using the Tsuji type configuration. To study the effect of porous burner diameter (D), ag values were obtained for four values of D at atmospheric pressure. The experimentally obtained ag for a given fuel-oxidizer combination decreases with an increase in burner diameter (D). This trend is consistent with the limited data available in the literature for hydrocarbon fuels. Other geometric and flow-field effects namely, (1) plug flow, (2) flow-field blocking by the burner, and (3) heat loss by the flame to sidewalls that can affect ag were also experimentally quantified. The results from this study show that the plug flow boundary condition is always satisfied for oxidizer inlet distance > 2 times the largest porous burner diameter. Burner diameter less than 1/4 times side wall length (as is the case for all burners used in this study) does not significantly modify the flow. Hence, these two flow-field modifications do not affect ag. However, heat loss from the flame to the ambient through the side walls can cause a 4–9 % decrease in ag. Experiments showed that, CO/H2 mixtures diluted with N2 yield 1.6–2.25 times higher ag in comparison to CO/H2 mixtures diluted with CO2. Increasing H2 from 1 to 5 % leads to 2.5–3.8 times increase in ag, compared to 5 to 10 % increase in H2 which leads to only 1.3–1.7 times increase in ag for 70 % of N2 (v/v) in fuel mixture. Global extinction strain rate (ag) increases by 1.5–2.4 times with 10 % increase in CO for fuel mixtures consisting of H2 (1 and 5 % by v/v), CO2 (50, 60 and 70 % by v/v) and N2 (50, 60, 70 and 80 % by v/v). The change in overall reactivity (ωo) due to different diluents is used to quantitatively explain the variation of ag for different fuel compositions. These effects are also qualitatively explained using OH radical concentration change with H2 % in the fuel mixtures.