Mechanism of detonation formation as a result of free flame propagation in unconfined space

2019 ◽  
Vol 489 (5) ◽  
pp. 461-464
Author(s):  
A. D. Kiverin ◽  
I. S. Yakovenko ◽  
V. E. Fortov
Keyword(s):  
Shock Waves ◽  
Flame Front ◽  
Flame Propagation ◽  
Linear Stage ◽  
Local Formation ◽  
Stage Of Development ◽  
Detonation Transition

The problem of the detonation formation as a result of unconfined flame propagation is solved numerically. The mechanism of detonation formation is distinguished. It is related to the local formation of shock waves du- ring the linear stage of development of flame front perturbations formed on the surface of the expanding flame front. General criteria of the establishment of the conditions for the detonation transition via the proposed mechanism are formulated.

scholarly journals Characteristics of Flame Propagation in a Vortex Flow for Deflagration-to-Detonation Transition

2014 ◽  
Vol 12 (ists29) ◽  
pp. Pe_35-Pe_41
Author(s):  
Katuo ASATO ◽  
Takeshi MIYASAKA ◽  
Takuya SUKEGAWA ◽  
Kouki TANABASHI ◽  
Atsuhiro KAWAMATSU ◽  
...  
Keyword(s):  
Flame Propagation ◽  
Vortex Flow ◽  
Deflagration To Detonation Transition ◽  
Detonation Transition

Role of Darrieus–Landau instability in propagation of expanding turbulent flames

2018 ◽  
Vol 850 ◽  
pp. 784-802 ◽  
Author(s):  
Sheng Yang ◽  
Abhishek Saha ◽  
Zirui Liu ◽  
Chung K. Law
Keyword(s):  
Flame Front ◽  
Flame Propagation ◽  
High Pressures ◽  
Turbulent Flame ◽  
Turbulent Flames ◽  
Scaling Analysis ◽  
Turbulent Eddies ◽  
Front Instability ◽  
Cellular Flame

In this paper we study the essential role of Darrieus–Landau (DL), hydrodynamic, cellular flame-front instability in the propagation of expanding turbulent flames. First, we analyse and compare the characteristic time scales of flame wrinkling under the simultaneous actions of DL instability and turbulent eddies, based on which three turbulent flame propagation regimes are identified, namely, instability dominated, instability–turbulence interaction and turbulence dominated regimes. We then perform experiments over an extensive range of conditions, including high pressures, to promote and manipulate the DL instability. The results clearly demonstrate the increase in the acceleration exponent of the turbulent flame propagation as these three regimes are traversed from the weakest to the strongest, which are respectively similar to those of the laminar cellularly unstable flame and the turbulent flame without flame-front instability, and thus validating the scaling analysis. Finally, based on the scaling analysis and the experimental results, we propose a modification of the conventional turbulent flame regime diagram to account for the effects of DL instability.

Experimental determination of flame speed and flame stretch using an optically accessible, spark-ignition engine

2019 ◽  
pp. 146808741987771 ◽  
Author(s):  
Behdad Afkhami ◽  
Yanyu Wang ◽  
Scott A Miers ◽  
Jeffrey D Naber
Keyword(s):  
Flame Front ◽  
Flame Propagation ◽  
Engine Speed ◽  
Spark Ignition ◽  
Flame Speed ◽  
Dominant Factor ◽  
Lean Mixture ◽  
Flame Stretch ◽  
Flame Development ◽  
The Rich

The current research experimentally studied flame speed and stretch under engine in-cylinder conditions. A direct-injection, spark-ignition, and optically accessible engine was utilized to image the flame propagation, and E10 was selected as the fuel. Also, three fuel–air mixtures (stoichiometric, lean, and rich) were examined. The flame front was located by processing high-speed images. This study introduces a novel approach for calculation of equivalent spherical flame radius for analysis of flame speed and stretch. Flame front propagation analysis showed that during the flame propagation period, the stretch decreased until the flame front touched the piston surface. This was a common trend for stoichiometric, lean, and rich mixtures, which occurred because the flame radius was the dominant factor in the stretch calculation. In addition, the rich fuel–air mixture showed a lower flame stretch compared to stoichiometric or lean mixture. This was the result of a lower Markstein number for the rich fuel–air mixture. To study the sensitivity of different fuel–air mixtures to the flame stretch, the trajectory of the flame centroid was tracked until the flame front touched the piston surface. The results showed that the end centroid for the lean mixture deviated from the start point more than those of the rich and stoichiometric mixtures because the lean mixture had a higher flame stretch and lower flame speed. Furthermore, comparing the flame stretch at three different engine speeds revealed that increasing the engine speed increased the flame stretch, especially during the early flame development period. According to previous studies which discussed flame stretch as a flame extinguishment mechanism, the probability of flame extinction is higher when the engine speed is higher. Also, uncertainty analysis was conducted to determine the effect of camera setting on the flame stretch. Results showed that a maximum relative uncertainty of 4.5% occurred during the early flame development.

The effect of the flame front structure on flame propagation in premixed gases

1982 ◽  
Vol 19 (1) ◽  
pp. 433-439 ◽  
Author(s):  
E. Hoffmann-Berling ◽  
R. Günther ◽  
W. Leuckel
Keyword(s):  
Flame Front ◽  
Flame Propagation ◽  
Front Structure

CFD Prediction for an Overpressure Buildup Phenomenon of SRI Hydrogen Test in an Open Space

2011 ◽  
Author(s):  
Hyung Seok Kang ◽  
Sang Baik Kim ◽  
Min-Hwan Kim ◽  
Hee Cheon No
Keyword(s):  
Flame Front ◽  
Flame Propagation ◽  
Spark Ignition ◽  
Cell Length ◽  
Cfd Analysis ◽  
Analysis Method ◽  
Step Size ◽  
Time Step ◽  
Time Step Size ◽  
Comparison Results

A computational fluid dynamics (CFD) calculation for a hydrogen explosion test with a complicated obstacle tube geometry of pitch 21.3mm and diameter 99.1mm at a stoichiometric condition was performed to establish a CFD analysis method for a hypothetical hydrogen explosion accident between a very high temperature reactor (VHTR) and a hydrogen production facility. We developed a spark ignition model to simulate high ignition energy of 40J induced by an electric device for 2 ms in the hydrogen explosion based on an energy conservation law. We performed a sensitivity calculation by varying a constant value of the eddy dissipation model (EDM), a time step size, and a cell length size around the obstacle tube to evaluate an effect of each factor on the flame propagation and overpressure buildup phenomenon. The CFD results of the flame front time of arrival (TOA) and overpressure were compared with those of the test data. The comparison results showed that the spark ignition model with a radius of 6 cm, a pressure of 105.7 kPa, a temperature of 1000 K, a turbulent mixing time of 2 ms, and an assumption of the 10% product mass fraction can reasonably initiate the hydrogen flame propagation in the CFD calculation. As for the CFD analysis method, the EDM constants of A = 10 and B = 0.8, the time step size of 0.01 ms, the cell length of 1 cm around the obstacle tube predicted the measured flame front TOA and peak overpressure with an error range of about 27.8% and 53.3%, respectively. Therefore, it is known that the CFD analysis with the EDM may be used as an accurate evaluation tool to provide the 3-dimesnional information of the flame front TOA and overpressure buildup phenomenon if the CFD analysis method is properly chosen.

Effect of Centrifugal Force on Turbulent Premixed Flames

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
Alejandro M. Briones ◽  
Balu Sekar ◽  
Timothy Erdmann
Keyword(s):  
Numerical Model ◽  
Flame Front ◽  
Centrifugal Force ◽  
Flame Propagation ◽  
Propagation Velocity ◽  
Turbulent Flame ◽  
Premixed Flames ◽  
Turbulent Premixed Flames ◽  
Flame Propagation Velocity ◽  
Turbulent Flame Speed

The effect of centrifugal force on flame propagation velocity of stoichiometric propane–, kerosene–, and n-octane–air turbulent premixed flames was numerically examined. The quasi-turbulent numerical model was set in an unsteady two-dimensional (2D) geometry with finite length in the transverse and streamwise directions but with infinite length in the spanwise direction. There was relatively good comparison between literature-reported measurements and predictions of propane–air flame propagation velocity as a function of centrifugal force. It was found that for all mixtures the flame propagation velocity increases with centrifugal force. It reaches a maximum, then falls off rapidly with further increases in centrifugal force. The results of this numerical study suggest that there are no distinct differences among the three mixtures in terms of the trends seen of the effect of centrifugal force on the flame propagation velocity. There are, however, quantitative differences. The numerical model is set in a noninertial, rotating reference frame. This rotation imposes a radially outward (centrifugal) force. The ignited mixture at one end of the tube raises the temperature and its heat release tends to laminarize the flow. The attained density difference combined with the direction of the centrifugal force promotes Rayleigh–Taylor instability. This instability with thermal expansion and turbulent flame speed constitute the flame propagation mechanism towards the other tube end. A wave is also generated from the ignition zone but propagates faster than the flame. During propagation the flame interacts with eddies that wrinkle and/or corrugate the flame. The flame front wrinkles interact with streamtubes that enhance Landau–Darrieus (hydrodynamic) instability, giving rise to a corrugated flame. Under strong stretch conditions the stabilizing equidiffusive-curvature mechanism fails and the flame front breaks up, allowing inflow of unburned mixture into the flame. This phenomenon slows down the flame temporarily and then the flame speeds up faster than before. However, if corrugation is large and the inflow of unburned mixture into the flame is excessive, the latter locally quenches and slows down the flame. This occurs when the centrifugal force is large, tending to blowout the flame. The wave in the tube interacts continuously with the flame through baroclinic torques at the flame front that further enhances the above mentioned flame–eddy interactions. Only at low centrifugal forces, the wave intermingles several times with the flame before the averaged flame propagation velocity is determined. The centrifugal force does not substantially increase the turbulent flame speed as commented by previous experimental investigations. The results also suggest that an ultracompact combustor (UCC) with high-g cavity (HGC) will be limited to centrifugal force levels in the 2000–3000 g range.

Deflagration to Detonation Transition of Explosives without the Effects of Shock Waves

2014 ◽  
Vol 1082 ◽  
pp. 399-402
Author(s):  
Xing Hua Xie ◽  
Kang Xu ◽  
Hui Sheng Zhou
Keyword(s):  
Thermal Decomposition ◽  
Shock Waves ◽  
Ammonium Nitrate ◽  
Hot Spot ◽  
Storage Process ◽  
Heat Accumulation ◽  
Emulsion Explosives ◽  
Deflagration To Detonation Transition ◽  
Detonation Transition ◽  
And Storage

Inthis paper, the deflagration to detonation transition in explosives without theeffects of detonators was studied by the analyzing the accident in theproduction and storage process of explosives. Combining the decompositionmechanism of ammonium nitrate in the emulsion explosives and the lessons fromthe production of emulsion explosives explosion, the conditions of the emulsionexplosives (matrix) thermal decomposition in the emulsifier are given that arethe formation of hot spot and the accumulation of heat. Then the factors of hotspots generated in the production of emulsion explosives and the occurredconditions of the heat accumulation are analyzed and summarized.

Experimental Study of Flame Stretch Under Engine-Like Conditions

2017 ◽  
Author(s):  
Behdad Afkhami ◽  
Yanyu Wang ◽  
Scott A. Miers ◽  
Jeffrey D. Naber
Keyword(s):  
Flame Front ◽  
Flame Propagation ◽  
High Speed ◽  
Combustion Engine ◽  
Turbulent Flame ◽  
Experimental Studies ◽  
Flame Velocity ◽  
Turbulent Flame Speed ◽  
Stretch Rate ◽  
Flame Stretch

Since fossil fuels will remain the main source of energy for power generation and transportation in next decades, their combustion processes remain an important concern for the foreseeable future. For liquid or gaseous fuels, flame velocity that propagates normal to itself and relative to the flow into the unburned mixture is one of the most important quantities to study. In a non-uniform flow, a curved flame front area changes continually which is known as flame stretch. The concept becomes more important when it is realized that the stretch affects the turbulent flame speed. The current research empirically studies flame stretch under engine-like conditions since there has not been enough experimental studies in this area. For this reason, a one-cylinder, direct-injection, spark-ignition, naturally-aspirated optical engine was utilized to image the flame propagation process inside an internal combustion engine cylinder on the tumble plane. The flame front was found by processing high speed images which were taken from the flame inside the cylinder. Flame front propagation analysis showed that after the flame kernel was developed, during flame propagation period, the stretch rate decreased until the flame front touches the piston surface. This trend was common among stoichiometric, lean, and rich mixtures. In addition, the fuel-air mixture with λ = 0.85 showed lower stretch rate compared to stoichiometric or lean mixture with λ = 1.2. However, based on previous studies, further enrichment may result in the flame stretch rate become greater than that of the stretch rates for stoichiometric or lean mixtures. Also, comparing the stretch rate at two different engine speeds revealed that as the speed increased the stretch rate also increased; especially during the early flame development period. Therefore, according to previous studies which discussed flame stretch as a mechanism for flame extinguishment, the probability of the flame extinction is higher when the engine speed is higher.

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