Role of atomic hydrogen diffusion in a hydrogen flame

A numerical modeling study of the propagation of a laminar flat homogeneous gas flame has shown that in a hydrogen-air flame, a rapid increase in the concentration of OH radicals begins in the range of low temperatures and the concentration profile has two maxima. The first maximum in the low-temperature region of the front is related to the diffusion of H atoms, formation of HO₂ radicals, and the quadratic branching reaction H + HO₂ → OH + OH. The second maximum in the OH concentration profile is due to the classical high-temperature branching reactions H + O₂ → OH + O and O + H₂ → OH + H. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 2, pp. 3–9, March–April, 2007.     

Velocity of combustion of a turbulent diffusion flame jet

Conclusions The investigation carried out showed that the velocity of transverse expansion of a reduced flow of combustion products can be used as the characteristic velocity of diffusion combustion, and the width of this flow can be used as a linear dimension, characterizing the degree of burnup.The physical basis for the velocity of diffusion combustion coincides completely with the well-known ideas in the literature concerning the velocity of laminar and turbulent homogeneous combustion, and therefore it is possible to compare the intensities of all three types of combustion. During the experimental investigations of turbulent homogeneous combustion, it was more useful to measure not the flame propagation velocity with respect to its leading edge, as is usually done, but the combustion velocity, which is unambiguously related to the rate of heat release.The preliminary comparison, carried out between the velocities of diffusion and homogeneous combustion, indicates the significant reduction of the heat-release intensity in a diffusion flame jet in comparison with a homogeneous flame jet, which, obviously, is explained by the complexity of the mixing process which precedes the chemical reaction.Institute of Problems of Mechanics, Academy of Sciences of the USSR, Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 12, No. 4, pp. 483–493, July–August, 1976.     

Role of atomic hydrogen diffusion in hydrogen flame inhibition

A laminar flame propagating in a rich homogeneous hydrogen-air mixture with addition of propylene is numerically simulated. Small amounts of propylene are shown to reduce the concentrations of HO₂ and OH in the low-temperature zone of the flame front, which effectively reduces the laminar burning velocity. In the flame front, propylene is consumed completely with formation of CO, CO₂, CH₄, C₂H₂, H₂, and H₂O, whereas hydrogen undergoes little oxidation compared to propylene. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 4, pp. 3–7, July–August, 2006.     

Calculation of diffusion turbulent flame from instantaneous parameters

Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 24, No. 2, pp. 90–92, March–April, 1988.     

Natural stabilization and disruption of damped turbulent diffusion of a gas flame

Balashikha. Translated from Fizika Goreniya i Vzryva, Vol. 27, No. 5, pp. 76–81, September–October, 1991.     

Study of the turbulent inverse diffusion flame in recessed backstep and coaxial burners

A comparative study of the turbulent Inverse Diffusion Flame (IDF) in recessed coaxial and backstep burners is carried out, based on visible flame appearance, flame length, flame stability, centerline temperature distribution, centerline oxygen concentration, and NO _x emissions. The backstep burner is observed to produce a compact flame shape with less luminosity at a higher air-fuel velocity ratio, as compared to the coaxial burner. Moreover, slightly better thermal characteristics and marginal reduction in NO _x emissions are provided by the backstep IDF, as compared to the recessed coaxial IDF. Besides this, the centerline oxygen concentration is marginally increased in the backstep IDF due to higher entrainment of ambient air. Interestingly, a lower flame stability limit is seen in the backstep burner than in the coaxial IDF, which can be attributed to its enhanced fuel-air mixing.     

Effects of hydrogen addition on flame structure and forced flame response to velocity modulation in a turbulent lean premixed combustor

Flame transfer function measurements were performed in a turbulent premixed lean combustor with various blends of hydrogen and natural gas. The fuel mixture was completely premixed with air upstream of a choked inlet to the combustor to avoid equivalence ratio fluctuations. A variable speed siren was used to modulate fluctuations in the inlet velocity, which was measured using a hot wire anemometer as an input parameter of the flame transfer function. Heat release oscillations as an output function were determined using chemiluminescence measurements from whole flames. Stable flame images were captured to understand general flame behavior over a range of operating conditions and fuel blends. Experimental results showed that the stable flames’ COMs (centers of mass) laid along a common path in a 2-D plane for all of the operating conditions and tested fuel compositions at a given injector geometry, and that variations in the stable flame shape could be characterized by the location of the common path of the flame’s COM. It was also shown that changes in the fuels significantly affected the flame shape; as a result, flame dynamics varied with changes in flame geometry. Accordingly, flames that were close together on the characteristic flame COM curve were shown to have similar forced flame responses.