scholarly journals The critical tube diameter and critical energy for direct initiation of detonation in C2H2/N2O/Ar mixtures

2012 ◽  
Vol 159 (9) ◽  
pp. 2944-2953 ◽  
Author(s):  
Bo Zhang ◽  
Hoi Dick Ng ◽  
John H.S. Lee
Keyword(s):  
Critical Energy ◽  
Tube Diameter ◽  
Direct Initiation ◽  
Critical Tube Diameter

The role of cellular instability on the critical tube diameter problem for unstable gaseous detonations

2019 ◽  
Vol 37 (3) ◽  
pp. 3545-3553 ◽  
Author(s):  
Han Xu ◽  
Xiaocheng Mi ◽  
Charles B. Kiyanda ◽  
Hoi Dick Ng ◽  
John H.S. Lee ◽  
...  
Keyword(s):  
Tube Diameter ◽  
Gaseous Detonations ◽  
Critical Tube Diameter

scholarly journals The role of unsteadiness in direct initiation of gaseous detonations

2000 ◽  
Vol 421 ◽  
pp. 147-183 ◽  
Author(s):  
CHRIS A. ECKETT ◽  
JAMES J. QUIRK ◽  
JOSEPH E. SHEPHERD
Keyword(s):  
Numerical Simulations ◽  
Decay Rate ◽  
Wave Front ◽  
Reaction Zone ◽  
Critical Energy ◽  
Local Analysis ◽  
Zone Structure ◽  
Gaseous Detonations ◽  
Release Wave ◽  
Direct Initiation

An analytical model is presented for the direct initiation of gaseous detonations by a blast wave. For stable or weakly unstable mixtures, numerical simulations of the spherical direct initiation event and local analysis of the one-dimensional unsteady reaction zone structure identify a competition between heat release, wave front curvature and unsteadiness. The primary failure mechanism is found to be unsteadiness in the induction zone arising from the deceleration of the wave front. The quasi-steady assumption is thus shown to be incorrect for direct initiation. The numerical simulations also suggest a non-uniqueness of critical energy in some cases, and the model developed here is an attempt to explain the lower critical energy only. A critical shock decay rate is determined in terms of the other fundamental dynamic parameters of the detonation wave, and hence this model is referred to as the critical decay rate (CDR) model. The local analysis is validated by integration of reaction-zone structure equations with real gas kinetics and prescribed unsteadiness. The CDR model is then applied to the global initiation problem to produce an analytical equation for the critical energy. Unlike previous phenomenological models of the critical energy, this equation is not dependent on other experimentally determined parameters and for evaluation requires only an appropriate reaction mechanism for the given gas mixture. For different fuel–oxidizer mixtures, it is found to give agreement with experimental data to within an order of magnitude.

scholarly journals Critical energy for direct initiation of spherical detonations in H2/N2O/Ar mixtures

2011 ◽  
Vol 36 (9) ◽  
pp. 5707-5716 ◽  
Author(s):  
Bo Zhang ◽  
Hoi Dick Ng ◽  
Rémy Mével ◽  
John H.S. Lee
Keyword(s):  
Critical Energy ◽  
Direct Initiation

The diffraction of a planar detonation wave at an abrupt area change

1979 ◽  
Vol 95 (1) ◽  
pp. 79-96 ◽  
Author(s):  
D. H. Edwards ◽  
G. O. Thomas ◽  
M. A. Nettleton
Keyword(s):  
Detonation Wave ◽  
Critical Diameter ◽  
Cylindrical Tube ◽  
Tube Diameter ◽  
Zone Length ◽  
Area Change ◽  
Expansion Fan ◽  
The One ◽  
Critical Tube Diameter ◽  
Smoked Foil

Previous experimental work on the diffraction of a detonation wave at a large and abrupt area change in a tube, has shown that every system is characterized by a critical tube diameter at which quenching of the detonation occurs. Zeldovich, Kogarko & Simonov (1956) established that the critical tube diameter, for the oxy-acetylene system with varying dilution of nitrogen, lies between 500 and 700 times the one-dimensional induction zone length. Later, Mitrovanov & Soloukhin (1964) discovered that, for the same system, the critical diameter is 10 or 13 times the transverse wave spacing for a flat channel and cylindrical tube respectively. The two results are shown to be equivalent and are confirmed by further experiments in a 75 × 6 mm channel in which the flow is two-dimensional.Smoked foil and schlieren records show that, for supercritical waves, re-ignition occurs at sites along the wedge formed by the head of the expansion from the diffracting aperture and criticality is attained when the site is located at the apex of the wedge. A universal feature of re-initiation, which is also observed in liquid and solid explosives, is the sudden appearance of a transverse detonation which sweeps through the compressed, but unreacted, gas of the dissociated shock-reaction zone regime; this is signalled by the appearance of fine triple-point writing on smoked-foil records.A criterion for re-initiation is formulated by equating the critical velocity gradient which characterizes the decay of the wavefront in a cell, to that obtaining in the diffracted shock front at the head of the expansion fan; an expression for the latter is derived from Whitham's (1957) theory for non-reactive shocks. The prediction of the criterion is in good agreement with observation.

scholarly journals Response of critical tube diameter phenomenon to small perturbations for gaseous detonations

Shock Waves ◽  
2013 ◽  
Vol 24 (2) ◽  
pp. 219-229 ◽  
Author(s):  
N. Mehrjoo ◽  
B. Zhang ◽  
R. Portaro ◽  
H. D. Ng ◽  
J. H. S. Lee
Keyword(s):  
Tube Diameter ◽  
Small Perturbations ◽  
Gaseous Detonations ◽  
Critical Tube Diameter
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