Burning Behaviour of High-Pressure CH4-H2-Air Mixtures

Abstract

Experimental characterization of the burning behavior of gaseous mixtures has been carried out, analyzing spherical expanding flames. Tests were performed in the Device for Hydrogen-Air Reaction Mode Analysis (DHARMA) laboratory of Istituto Motori-CNR. Based on a high-pressure, constant-volume bomb, the activity is aimed at populating a systematic database on the burning properties of CH 4 , H 2 and other species of interest, in conditions typical of internal combustion (i.c.) engines and gas turbines. High-speed shadowgraph is used to record the flame growth, allowing to infer the laminar burning parameters and the flame stability properties. Mixtures of CH 4 , H 2 and air have been analyzed at initial temperature 293÷305 K, initial pressure 3÷18 bar and equivalence ratio  = 1.0. The amount of H 2 in the mixture was 0%, 20% and 30% (vol.). The effect of the initial pressure and of the Hydrogen content on the laminar burning velocity and the Markstein length has been evaluated: the relative weight and mutual interaction has been assessed of the two controlling parameters. Analysis has been carried out of the flame instability, expressed in terms of the critical radius for the onset of cellularity, as a function of the operating conditions.

Buoyant Unstable Behavior of Initially Spherical Lean Hydrogen-Air Premixed Flames

“…According to the previously reported results [10][11][12][13], the flame front of premixed hydrogen-air flames will be continuously wrinkled towards cellular instability during the propagation. There exist three intrinsic factors to induce an unstable premixed flame-hydrodynamic effects, thermal-diffusive effects, and buoyant effects [14].…”

“…There exist three intrinsic factors to induce an unstable premixed flame-hydrodynamic effects, thermal-diffusive effects, and buoyant effects [14]. The hydrodynamic instability is induced by the thermal expansion across the flame front [15], which has been proved to be present for all premixed flames and whose intensity is always indicated by the density ratio between the two sides of the flame front [8][9][10][11][12][13][14]; the thermal-diffusive instability is induced by the competing effects between heat conduction from the flame and the reactant diffusion towards the flame, and the intensity is always indicated by the Lewis number (which is defined as the ratio of the thermal diffusivity to the mass diffusivity) [16]; and the buoyant instability is commonly regarded as be relevant to body-force.…”

The impact of hydrogen enrichment on the flow field evolution in turbulent explosions

“…Moccia and D'Alessio [50] studied spherically expanding flames in stoichiometric CH 4 /H 2 mixtures with 10%, 20% and 30% H 2 at elevated initial pressures (3, 6 and 12 bar). An earlier onset of the cellular structure was observed with increased H 2 fractions.…”

Research on Cellular Instabilities of Lean Premixed Syngas Flames under Various Hydrogen Fractions Using a Constant Volume Vessel

“…The diffusive-thermal instability is caused by the competing effects of heat conduction and the reactant diffusion [45] and can always be quantitatively determined using the Lewis number (Le), which is defined as the ratio of the heat diffusivity to mass diffusivity of the deficient reactant to the abundant inert [46] and is used to describe diffusive-thermal instabilities, Le H2 and Le CO can be calculated as expressed by the equation:…”