Experimental characterization of galloping detonations in unstable mixtures

Gao, Yuan; Ng, Hoi Dick; Lee, John H. S.

doi:10.1016/j.combustflame.2015.02.007

Cited by 47 publications

(13 citation statements)

References 31 publications

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“…This result may also have relevance to the phenomenon of galloping detonation, wherein steady detonation propagation is not possible due to the tube diameter being smaller than a characteristic cell size required for propagation, such that the detonation fails to approximately half CJ speed and periodically reinitiates to an initially overdriven wave via a process similar to deflagration to detonation transition (DDT). Despite the fact that the cycle of the galloping detonation occurs over hundreds of tube diameters and the wave should experience significant heat and momentum losses due to the relatively small size of the tube used, galloping detonations continue to propagate remarkably close to the CJ speed on average [31,17,24]. This aspect of the discrete source detonation model has been further explored by Radulescu & Shepherd [47].…”

Section: Discussionmentioning

confidence: 99%

Effect of spatial discretization of energy on detonation wave propagation

Timofeev

Higgins

2017

J. Fluid Mech.

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Detonation propagation in the limit of highly spatially discretized energy sources is investigated. The model of this problem begins with a medium consisting of a calorically perfect gas with a prescribed energy release per unit mass. The energy release is collected into sheet-like sources that are now embedded in an inert gas that fills the spaces between them. The release of energy in the first sheet results in a planar blast wave that propagates to the next source, which is triggered after a prescribed delay, generating a new blast, and so forth. The resulting wave dynamics as the front passes through hundreds of such sources is computationally simulated by numerically solving the governing one-dimensional Euler equations in the lab-fixed reference frame. Two different solvers are used: one with a fixed uniform grid and the other using an unstructured, adaptively refined grid enabling the limit of highly concentrated, spatially discrete sources to be examined. The two different solvers generate consistent results, agreeing within the accuracy of the measured wave speeds. The average wave speed for each simulation is measured once the wave propagation has reached a quasi-periodic solution. The effect of source delay time, source energy density, specific heat ratio, and the spatial discreteness of the sources on the wave speed is studied. Sources fixed in the lab reference frame versus sources that convect with the flow are compared as well. The average wave speed is compared to the ideal Chapman-Jouguet (CJ) speed of the equivalent homogenized media. Velocities in excess of the CJ speed are found as the sources are made increasingly discrete, with the deviation above CJ being as great as 15%. The deviation above the CJ value increases with decreasing values of specific heat ratio γ. The total energy release, delay time, and whether the sources remain lab-fixed or are convected with the flow do not have a significant influence on the deviation of the average wave speed away from CJ. A simple, ad hoc analytic model is proposed to treat the case of zero delay time (i.e., source energy released at the shock front) that exhibits qualitative agreement with the computational solutions and may explain why the deviation from CJ increases with decreasing γ. When the sources are sufficiently spread out so as to make the energy release of the media nearly continuous, the classic CJ solution is obtained for the average wave speed. Such continuous waves can also be shown to have a time-averaged structure consistent with the classical ZND structure of a detonation. In the limit of highly discrete sources, temporal averaging of the wave structure shows that the effective sonic surface does not correspond to an equilibrium state. The average state of the flow leaving the wave in this case does eventually reach the equilibrium Hugoniot, but only after the effective sonic surface has been crossed. Thus, the super-CJ waves observed in the limit of highly discretized sources can be understood as weak detonations due to the...

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Section: Discussionmentioning

confidence: 99%

Effect of spatial discretization of energy on detonation wave propagation

Timofeev

Higgins

2017

J. Fluid Mech.

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“…1). A spark plug was connected to the ignition system in the driver section to generate a high energy spark as in our previous studies [18,23,24,[31][32][33]. A short length of Shchelkin spiral was also inserted just downstream of the spark plug to promote detonation formation.…”

Section: Methodsmentioning

confidence: 99%

An experimental investigation of detonation limits in hydrogen–oxygen–argon mixtures

Gao

Zhang

et al. 2016

International Journal of Hydrogen Energy

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The present paper reports the results of an experimental study of detonation limits for H2/O2/Ar mixtures. Two stoichiometric mixtures (2H2 + O2 + 3Ar and 2H2 + O2) in three different diameter round tubes (D = 1.8, 4.6 and 10.9 mm) were tested. The choice of the mixture represents those considered as "stable" with a regular cellular pattern and "unstable" with an irregular cellular pattern. Detonation velocity was measured by ionization probes spaced at regular intervals along the small tubes. Consistent with previous findings, the present results show that well within the limits the detonation wave in hydrogen mixtures propagates at a steady velocity close to the theoretical Chapman-Jouguet (CJ) value. With decreasing initial pressure, the velocity deficit increases. It is found that the detonation velocity decreases with decreasing tube diameter, which is a result of the wall boundary layer effect being more prominent for smaller tubes. At the limiting pressure, the steady velocity deficit for both tested mixtures in three different diameter tubes is about 15−18%. Velocity deficits were also estimated theoretically using the Fay model. For the stable mixture good agreement is found between the theoretical prediction and the experimental result of detonation velocity. For the unstable mixture, however, the theoretical prediction deviates from the experimental measurement. The latter thus suggests that, apart from losses due to the flow divergence caused by the boundary layer effect, instabilities are also significant for the detonation propagation and failure in unstable mixtures. Lastly, at the limits, the value of D/λ is found to agree well with that for the onset of single-headed spin detonation. Thus, it can be concluded that the single-headed spin criterion can also be used for defining the detonation limits for hydrogen mixtures.

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“…The limit can be initial pressure or chemical composition. In the past, studies related to the detonation limits were mostly conducted in smooth circular tubes [6,[100][101][102][103][104][105][106]. It is important to underline that the limits in aforementioned literatures are the critical initial pressure.…”

Section: Detonation Quenchingmentioning

confidence: 99%

“…The spinning detonation can still hold a stable velocity within 0.8 V CJ . At the limits, other detonation modes may appear, such as galloping mode [102,103]. The galloping mode often occurs in unstable mixtures in small diameter tubes, with significant velocity fluctuation (0.4V CJ 1.5 V CJ ) [103].…”

Section: Detonation Quenchingmentioning

confidence: 99%

Flame quenching by crimped ribbon flame arrestor: A brief review

Wang

Shen

et al. 2018

Process Safety Progress

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Accidental explosions in gas/oil pipelines remain one major concern in process industries. The crimped ribbon flame arrestor is an effective device to prevent flame propagation. This review summarizes existing knowledge on the quenching of flame of different regimes in narrow channels and crimped ribbon flame arrestors. The influences of various parameters (e.g., arrestor element thickness, expansion ratio, system pressure) on the performance of crimped ribbon flame arrestors are discussed. The presented discussions give a better understanding on the considerations which must be taken into account to quench an explosion successfully. Other scenarios, such as quenching of two-phase vapor-liquid explosions and overdriven detonations should be got further attention. Figure 18. The results of quenching ethylene/air/oxygen flames by a DN50 flame arrestor [114]. Black dot: flame quenched; red cross: flame not quenched. [Color figure can be viewed at wileyonlinelibrary.com]

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Experimental characterization of galloping detonations in unstable mixtures

Cited by 47 publications

References 31 publications

Effect of spatial discretization of energy on detonation wave propagation

Effect of spatial discretization of energy on detonation wave propagation

An experimental investigation of detonation limits in hydrogen–oxygen–argon mixtures

Flame quenching by crimped ribbon flame arrestor: A brief review

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