Suppression effects of diluents on laminar premixed hydrogen/oxygen/nitrogen flames

A study of the effects of diluents on near-limit H2–air flames in microgravity at normal and reduced pressures

“…No results were considered where the flame surface was found to be wrinkled due to flame instabilities. Similar to previous measurements of laminar premixed flame properties [1,2], measurements were also limited to δ D /r f < 0.05, where δ D is the characteristic flame thickness and r f is the flame radius, so that effects of curvature and transient phenomena associated with large flame thickness during the early stages of flame formation were small. Under these assumptions, quasi-steady expressions for the local laminar burning velocity and flame stretch are given by [3] (1)…”

“…In a previous study [1], we reported results on the effectiveness of various diluents at relatively low concentrations for outwardly propagating, spherical, premixed flames under normal-gravity conditions. The diluents considered were helium, argon, nitrogen, and carbon dioxide.…”

“…As diluent concentrations increase and the extinction limit is approached, however, the normalgravity flames in Ref. [1] cannot be used to investigate the near-limit properties and flammability limits that are essential to characterizing flame-suppression effectiveness under microgravity conditions. Motivated by this, we designed and built a shortdrop free-fall facility in the laboratory to eliminate the intrusion of buoyancy on near-extinction flames, which was reported in Ref [2].…”

Effect of Hydrogen Content and Dilution on Laminar Burning Velocity and Stability Characteristics of Producer Gas-Air Mixtures

“…Kwon and Faeth [13] have shown a similar result for H 2 -O 2 -Ar mixtures: at φ = 0.6, with variation of O 2 /(O 2 +Ar) from 0.36 to 0.21, H 2 /O 2 /Ar mixtures also showed a transition from stable to unstable condition. Also Qiao et al [26] have shown that for H 2 -air mixtures at φ = 1 an increase in dilution with Ar, N 2 , or CO 2 from 0%-40% results in transition from stable to unstable condition. Taylor [19] found that with dilution of H 2 -air mixture with nitrogen from 0-60%, Markstein number changed from positive to negative values, signifying transition.…”

Measurement of laminar burning velocities and analysis of flame stabilities for hydrogen-air-diluent premixed mixtures

“…Hermanns et al [9] , by using the heat flux method and nitrogen as the diluent, measured the laminar burning velocity of hydrogen-airdiluent mixture at equivalence ratios ranging from 0.7 to 3.1. Other researchers also measured the laminar burning velocities of the diluted hydrogen-air mixtures (nitrogen and/or carbon dioxide as the diluent) at limited equivalence ratios, using the high-speed schlieren photography and a constant volume chamber [10][11][12][13][14][15][16][17][18][19] . However, the above researches only covered a narrow range of equivalence ratio, and the separate use of nitrogen or carbon dioxide as the diluent cannot give an overall understanding of combustion of the hydrogen-air-diluent mixture.…”