scholarly journals Measurement and scaling analysis of critical energy for direct initiation of gaseous detonations

Shock Waves ◽  
2011 ◽  
Vol 22 (3) ◽  
pp. 275-279 ◽  
Author(s):  
B. Zhang ◽  
H. D. Ng ◽  
J. H. S. Lee
Keyword(s):  
Critical Energy ◽  
Scaling Analysis ◽  
Gaseous Detonations ◽  
Direct Initiation

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

On the direct initiation of gaseous detonations by an energy source

1994 ◽  
Vol 277 ◽  
pp. 227-248 ◽  
Author(s):  
Longting He ◽  
Paul Clavin
Keyword(s):  
Energy Source ◽  
Critical Radius ◽  
Critical Value ◽  
Blast Waves ◽  
Initiation Energy ◽  
Point Energy ◽  
Gaseous Detonations ◽  
Curvature Effects ◽  
Direct Initiation ◽  
Steady Solutions

A new criterion for the direct initiation of cylindrical or spherical detonations by a localized energy source is presented. The analysis is based on nonlinear curvature effects on the detonation structure. These effects are first studied in a quasi-steady-state approximation valid for a characteristic timescale of evolution much larger than the reaction timescale. Analytical results for the square-wave model and numerical results for an Arrhenius law of the quasi-steady equations exhibit two branches of solutions with a C-shaped curve and a critical radius below which generalized Chapman–Jouguet (CJ) solutions cannot exist. For a sufficiently large activation energy this critical radius is much larger than the thickness of the planar CJ detonation front (typically 300 times larger at ordinary conditions) which is the only intrinsic lengthscale in the problem. Then, the initiation of gaseous detonations by an ideal point energy source is investigated in cylindrical and spherical geometries for a one-step irreversible reaction. Direct numerical simulations show that the upper branch of quasi-steady solutions acts as an attractor of the unsteady blast waves originating from the energy source. The critical source energy, which is associated with the critical point of the quasi-steady solutions, corresponds approximately to the boundary of the basin of attraction. For initiation energy smaller than the critical value, the detonation initiation fails, the strong detonation which is initially formed decays to a weak shock wave. A successful initiation of the detonation requires a larger energy source. Transient phenomena which are associated with the intrinsic instability of the quasi-steady detonations branch develop in the induction timescale and may induce additional mechanisms close to the critical condition. In conditions of stable or weakly unstable planar detonations, these unsteady phenomena are important only in the vicinity of the critical conditions. The criterion of initiation derived in this paper works to a good approximation and exhibits the huge numerical factor, 106–108, which has been experimentally observed in the critical value of the initiation energy.

Internal pressure loads due to gaseous detonations

1993 ◽  
Vol 443 (1918) ◽  
pp. 343-366 ◽  
Keyword(s):  
Strong Shock ◽  
Shock Pressure ◽  
Gaseous Detonation ◽  
Flat Surfaces ◽  
Gaseous Detonations ◽  
Reflected Shock ◽  
Several Variables ◽  
Direct Initiation ◽  
Detonation Transition ◽  
Inert Layer

The internal loading of structures and confinements by gaseous detonation is studied using a multidimensional strong-shock physics code. Hydrogen-air-steam mixtures are used in calculations to show phenomena that apply qualitatively to any detonable gaseous fuel-oxidant-diluent mixture. Several variables are considered with respect to loading: ( a ) inert layers of various thicknesses; ( b ) deflagration-to-detonation transition(DDT) location as compared with direct initiation; and ( c ) some variations in geometry or confinement. Relatively thin inert layers are shown to increase the peak reflected shock pressure over that which would occur if the inert layer were not there. Inert layers may also increase impulse under some circumstances. DDT increases peak reflected pressures over those seen for direct initiation because of precompression of unburned gases. DDT may also increase impulses. Peak reflected pressures and impulses are greater in edges and corners than on flat surfaces. Internal obstruction tends to randomize the energy in a detonation wave, decreasing the impulse on structures, and allowing the pressure to equilibrate more rapidly than if there were no obstruction.

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