Experimental and theoretical analysis of cellular instability in lean H 2 -CH 4 -air flames at elevated pressures

Okafor, Ekenechukwu C.; Nagano, Yukihide; Kitagawa, Toshiaki

doi:10.1016/j.ijhydene.2016.02.151

Cited by 71 publications

(10 citation statements)

References 47 publications

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“…The first is dominated by the adiabatic explosion pressure, while the latter is related to the propagation speed of the blast wave during explosion. Different to other fuels, hydrogen gas has a stronger diffusion-thermal characteristic [16][17][18][19], which makes the values of adiabatic explosion pressure close for the case of the stoichiometric and φ = 1.2 levels, obviously higher than those in the cases whose equivalence ratio outside the range of 1.0-1.2 and, thus, it results in p max being attained in the case of φ = 1.0-1.2. However, like most practical thermal or power devices, the explosion vessel is not an adiabatic system and certain amounts of released heat is lost during the explosion process for the temperature drop across the vessel's wall and, resultantly, the actual value of p max is less than the adiabatic explosion pressure.…”

Section: Resultsmentioning

confidence: 99%

Explosion Behaviour of 30% Hydrogen/70% Methane-Blended Fuels in a Weak Turbulent Environment

Sun

2017

Energies

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In the present investigation the explosion characteristics of 30% H 2 /70% CH 4-blended fuels have been experimentally studied in different turbulent environments. Some important indicators about the explosion characteristics, including maximum explosion pressure (p max), explosion duration (t c), maximum rate of pressure rise ((dp/dt) max), deflagration index (K G), and fast burn period (t b) have been studied. Furthermore, the influences of turbulent intensity associated with the equivalence ratio on explosion characteristics have been compressively analysed. The results indicated that, with the increase of turbulent intensity (u' rms), the value of p max will be correspondingly raised while the equivalent ratio (φ) corresponding to the peak value of p max gradually changes from stoichiometric to 1.2. Based upon the value of p max in laminar condition, the growth extent of p max monotonically rises to u' rms , but under a same u' rms the growth extent of p max first declines and then rises with the increase of φ in the rage of 0.6 to 1.2. Under a laminar environment, the peak value of (dp/dt) max is attained at φ = 1.0; although such a conclusion is maintained in the studied range of turbulent intensity, the difference on the value of (dp/dt) max between φ = 1.0 and φ = 1.2 is obviously reduced with the increase of u' rms. Meanwhile, from the variation of K G , it could be found that turbulence can raise the hazardous potential of disaster. With the increase of u' rms , both the values of t c and t b reduce, the quota of t b in the explosion performs a similar regulation, but the detailed variation extent is also controlled by u' rms .

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Section: Resultsmentioning

confidence: 99%

Explosion Behaviour of 30% Hydrogen/70% Methane-Blended Fuels in a Weak Turbulent Environment

Sun

2017

Energies

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“…The flames can be observed in the chamber through the optical windows up to a diameter of 60 mm. The flames propagated at constant pressure from the time of ignition until their diameter was about 60 mm [26][27][28].…”

Section: Experimental Setup and Conditionsmentioning

confidence: 99%

“…The relationship between flame speed, Sn, and flame stretch rate, α, is given in Figure 3. Unstretched laminar burning velocity, SL, evaluations were conducted with Equation 6where ρ u and ρ b are unburnt mixture and burnt gas density, respectively [5,17,24,28]. Figure 5, the solid lines show the experimental results while the dashed lines show the outcome of numerical investigation using CHEMKIN-PRO.…”

Section: Experimental Setup and Conditionsmentioning

confidence: 99%

Experimental and Numerical Investigation of Laminar Burning Velocities of Artificial Biogas Under Various Pressure and CO₂ Concentration

et al. 2019

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As a renewable and sustainable fuel made from digestion facility, biogas is composed predominantly of methane (CH4) and carbon dioxide (CO2). CO2 in biogas strongly affects its combustion characteristics. In order to develop efficient combustors for biogas, fundamental flame characteristics of biogas require extensive investigation. In understanding the influence of CO2 concentration and mixture pressure on biogas combustion, the effects of CO2 concentration on the laminar burning velocity of methane/air mixtures were studied at different pressures. The studies were conducted using both numerical and experimental methods. The experiment was conducted using a constant volume high pressure combustion chamber. The propagating flames were recorded with a high speed digital camera by employing Schlieren photography technique. The numerical simulation was carried by utilizing CHEMKIN-PRO with GRI-Mech 3.0 employed as the chemical kinetics model. The results show that the laminar burning velocity of methane-air mixtures decreased with an increase in CO2 concentration and mixture pressure. Therefore, the burning velocity of biogas mixtures may decrease as the amount of CO2 in the gas increases.

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“…Cellular structures formed on the flame front increase the flame surface area and cause flame self-acceleration [26]. In this regard, Markstein length and cellular instability for various fuel/oxidizer mixtures have been studied extensively [27][28][29][30][31]. Laminar flame characteristics of butanol have been widely studied by various methods of experimental measurement and mechanism prediction [24,32,33].…”

Section: Introductionmentioning

confidence: 99%

Experimental and kinetic study on the laminar burning speed, Markstein length and cellular instability of oxygenated fuels

Qiao

Sun

Lin

et al. 2021

Fuel

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The laminar burning speed, Markstein length and cellular instability of three oxygenated fuels, polyoxymethylene dimethyl ether 3 (PODE3), dimethyl carbonate (DMC) and n-butanol (NB), were experimentally studied using spherical flame propagation method. Both of the three fuels are potential alternatives for petrochemical gasoline and diesel. Laminar burning speeds and Markstein lengths were measured at ambient pressure and elevated temperature (363 K-423 K) with three extrapolation models including linear and non-linear employed to extract the unstretched flame speed. Onset of flame cellular instability of the three fuels was determined at high pressure (0.5-0.75 MPa) which was favored to the occurrence of cellular instability. Three well-validated mechanisms for PODE3, DMC and NB respectively were used to numerically analyze the flame structure and then understand the underlying effect of the molecular structure of oxygenated fuels on laminar flame propagation. Results show that PODE3 has the highest laminar burning speed among the three, supporting by both thermal effect and kinetic effect. While the laminar burning speed of NB is higher than that of DMC, which is due to the combined effect of thermal factor and kinetic factor. The molecular structure of oxygenated fuels exerts an influence on the laminar flame propagation through the fuel-specific cracking pathway and resulting formed intermediates with different reactivity. The absence of C-C bond within PODE3 and DMC leads to the formation of substantial oxy-intermediates (CH2O) with high reactivity during fuel decomposition. PODE3 has the most stable flame among the three because of the strong stretching of PODE3 flame. The flame stability of DMC and NB is approximately similar especially at high initial pressure.

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Experimental and theoretical analysis of cellular instability in lean H 2 -CH 4 -air flames at elevated pressures

Cited by 71 publications

References 47 publications

Explosion Behaviour of 30% Hydrogen/70% Methane-Blended Fuels in a Weak Turbulent Environment

Explosion Behaviour of 30% Hydrogen/70% Methane-Blended Fuels in a Weak Turbulent Environment

Experimental and Numerical Investigation of Laminar Burning Velocities of Artificial Biogas Under Various Pressure and CO₂ Concentration

Experimental and kinetic study on the laminar burning speed, Markstein length and cellular instability of oxygenated fuels

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Experimental and theoretical analysis of cellular instability in lean H 2 -CH 4 -air flames at elevated pressures

Cited by 71 publications

References 47 publications

Explosion Behaviour of 30% Hydrogen/70% Methane-Blended Fuels in a Weak Turbulent Environment

Explosion Behaviour of 30% Hydrogen/70% Methane-Blended Fuels in a Weak Turbulent Environment

Experimental and Numerical Investigation of Laminar Burning Velocities of Artificial Biogas Under Various Pressure and CO2 Concentration

Experimental and kinetic study on the laminar burning speed, Markstein length and cellular instability of oxygenated fuels

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Experimental and Numerical Investigation of Laminar Burning Velocities of Artificial Biogas Under Various Pressure and CO₂ Concentration