Prediction of the liftoff, blowout and blowoff stability limits of pure hydrogen and hydrogen/hydrocarbon mixture jet flames

Abstract

The paper presented experimental studies of the liftoff and blowout stability of pure hydrogen, hydrogen/propane and hydrogen/methane jet flames using a 2 mm burner. Carbon dioxide and Argon gas were also used in the study for the comparison with hydrocarbon fuel. Comparisons of the stability of H 2 /C 3 H 8 , H 2 /CH 4 , H 2 /Ar and H 2 /CO 2 flames showed that H 2 /C 3 H 8 produced the highest liftoff height and H 2 /CH 4 required highest liftoff and blowoff velocities. The non-dimensional analysis of liftoff height approach was used to correlate liftoff data of H 2, H 2 -C 3 H 8 , H 2 -CO 2 , C 3 H 8 and H 2 -Ar jet flames tested in the 2 mm burner. The suitability of extending the empirical correlations based on hydrocarbon flames to both hydrogen and hydrogen/hydrocarbon flames was examined. INTRODUCTIONThe stabilization mechanisms of turbulent jet flames have been the topic of many papers and the most recent review was given by Peters [1]. It has emerged that the most successful theories to explain and predict the liftoff height location are the premixed flame propagation models [2][3][4][5][6][7] based on proposal by Vanquickenborne and van Tiggelen [2]. The importance of the isothermal mixing process of the jet was emphasised by Pitts [3][4][5]. The turbulent burning velocity has been one of the focused points for discussion using the premixed flame stabilization approach. Kalghatgi [6] assumed that the ratio of burning velocity to laminar burning velocity was proportional to the square root of the local turbulence Reynolds number based on the integral length scale. He successfully correlated the experimental data for CH 4 , C 2 H 4 , C 3 H 8 and H 2 into a single formula. More recent studies focused on the role of intermittence and large scale eddies and associated with premixed combustion by Broadwell et al. [7] and Burgess and Lawn [8]. Experimental studies of the large scale vortical structures in lifted flame were carried out by Schefer et al [9-10] using planar images of CH 4 , CH and temperature.So far most jet flame researchers have used pure hydrocarbon fuels or fuels diluted with air or nitrogen. Empirical correlations were developed to predict flame stability limits for pure and inert gas diluted hydrocarbon fuels. As hydrogen is becoming an important part of energy sector, there is a need to study the stability characteristics of both hydrogen and hydrogen/hydrocarbon flames. Studies on stability of hydrogen/hydrocarbon blended fuels are scarce. Recently, the stability of hydrogen and natural gas blended fuel was discussed by Choudhuri and Gollahalli [11]. The effect of hydrogen addition into methane on the flame stability under fuel lean condition was studied by Schefer [12] using swirlstabilized flame. However it is not clear if the established premixed flame propagation models can be applied to jet flames of blended fuels. It is also necessary to examine the suitability of extending the empirical correlations based on hydrocarbon flames to both hydrogen and hydrogen/hydrocarbon fl...

Hydrodynamic Vortex Structures in a Diffusion Jet Flame

“…Conditions for the jet flame extinction, i.e., the correlation of the cross flow velocity at which extinction occurs, fuel jet velocity, and other factors have been well established for hydrocarbon fuels. Recently, the conditions for stable burning of a jet flame of hydrogen fuel diluted with hydrocarbons (CO 2 ,CH 4 ,C 3 H 8 )in still air were investigated in [32]. The paper showed how additives of various gases affect the transition from the attached flame to the lifted one.…”

Jet flame heights, lift-off distances, and mean flame surface density for extensive ranges of fuels and flow rates

“…5. Originally, the density ratio at the exit plane, ( e / a ), was raised to a power of 1.5, but after further studies by Wu et al [66,67] this power was changed to 1.0, as in Fig. 5.…”

The impact of hydrogen enrichment and bluff-body lip thickness on characteristics of blended propane/hydrogen bluff-body stabilized turbulent diffusion flames

“…These fuels accelerate the reaction rate of burning which achieves improved ignitability and flame holding. This implies the burner to operate stably in lean and ultra-lean fuel to air ratios which in itself reduces the emission of pollutants such as carbon monoxide (CO), unburned hydrocarbons (UHC) and nitrogen oxides (NO x ) [3].…”