scholarly journals Numerical Simulation of the Deflagration-to-Detonation Transition in Inhomogeneous Mixtures

2014 ◽  
Vol 2014 ◽  
pp. 1-15 ◽  
Author(s):  
Florian Ettner ◽  
Klaus G. Vollmer ◽  
Thomas Sattelmayer
Keyword(s):  
Hydrogen Content ◽  
Concentration Gradient ◽  
Concentration Gradients ◽  
Deflagration To Detonation Transition ◽  
New Findings ◽  
Safety Studies ◽  
Geometric Boundary ◽  
Detonation Transition ◽  
Coarse Grids ◽  
Good Agreement

In this study the hazardous potential of flammable hydrogen-air mixtures with vertical concentration gradients is investigated numerically. The computational model is based on the formulation of a reaction progress variable and accounts for both deflagrative flame propagation and autoignition. The model is able to simulate the deflagration-to-detonation transition (DDT) without resolving all microscopic details of the flow. It works on relatively coarse grids and shows good agreement with experiments. It is found that a mixture with a vertical concentration gradient can have a much higher tendency to undergo DDT than a homogeneous mixture of the same hydrogen content. In addition, the pressure loads occurring can be much higher. However, the opposite effect can also be observed, with the decisive factor being the geometric boundary conditions. The model gives insight into different modes of DDT. Detonations occurring soon after ignition do not necessarily cause the highest pressure loads. In mixtures with concentration gradient, the highest loads can occur in regions of very low hydrogen content. These new findings should be considered in future safety studies.

Effect of Solute Concentration Gradients on the Onset of Convection: Uniform and Nonuniform Initial Gradients

1986 ◽  
Vol 108 (4) ◽  
pp. 776-782 ◽  
Author(s):  
M. Kaviany ◽  
M. Vogel
Keyword(s):  
Temperature Gradient ◽  
Concentration Gradient ◽  
Fluid Layer ◽  
Onset Time ◽  
Solute Concentration ◽  
Concentration Gradients ◽  
Linear Amplification ◽  
Onset Of Convection ◽  
Gradient Layer ◽  
Good Agreement

The time of the onset of convection in a fluid layer, which is initially stably stratified and then heated from below in a transient manner, is determined experimentally and analytically. The initial stratification is due to the presence of a solute concentration gradient. In addition to initial linear solute concentration distributions two other specific initial solute concentration distributions are considered. In Case 1, a zero gradient layer is located underneath a nonzero and uniform gradient layer. In Case 2, the zero gradient layer is on the top. The linear amplification theory is applied to the prediction of the onset time. Interferometry is used as a means of determining the onset time experimentally. It is shown that since the adverse temperature gradient is concentrated near the bottom, any nonuniformity in the solute concentration gradient in this region reduces the effectiveness of the gradient in delaying the onset. Experimental and predicted results are in good agreement.

Estimation of critical conditions for deflagration-to-detonation transition in obstructed channels filled with gaseous mixtures

2018 ◽  
Vol 13 (6) ◽  
pp. 54 ◽  
Author(s):  
Alexey D. Kiverin ◽  
Ivan S. Yakovenko
Keyword(s):  
Complex Analysis ◽  
Complex Geometry ◽  
Critical Conditions ◽  
Gaseous Mixtures ◽  
Flame Acceleration ◽  
Deflagration To Detonation Transition ◽  
Detonation Transition ◽  
The Stability ◽  
The Given ◽  
Good Agreement

The paper considers the peculiarities of deflagration-to-detonation transition (DDT) in obstructed channels filled with gaseous mixtures. The necessary stage in flame evolution prior to DDT is the stage of flame propagation in so-called “chocked flame” regime. The structure of the chocked flame is studied numerically in details that allows formulating the criterion of its stability. In turn, the stability of chocked flame determines the possibility of further flame acceleration and subsequent DDT. Such a criterion is of purely chemical nature and can be estimated using the parametric study involving simple one-dimensional calculations. It should be however noted that to get the prediction of DDT in real complex geometry one should additionally estimate the particular conditions of chocked flame formation in the given geometry. Moreover, the particular mechanisms of detonation onset should be analyzed. Such a complex analysis involving both chemical criterion and analysis of geometrical conditions is applied to the estimation of DDT possibility in obstructed channels. The obtained results are in a good agreement with available experimental data.

RANKING OF FUEL-AIR MIXTURES IN TERMS OF THEIR PROPENSITYTO DEFLAGRATION-TO-DETONATION TRANSITION

2020 ◽  
Author(s):  
S. M. FROLOV ◽  
◽  
V. I. ZVEGINTSEV ◽  
V. S. AKSENOV ◽  
I. V. BILERA ◽  
...  
Keyword(s):  
Detonation Wave ◽  
The Other ◽  
Practical Application ◽  
Deflagration To Detonation Transition ◽  
Other Hand ◽  
Pressure Gain Combustion ◽  
Reactive Mixture ◽  
Detonation Transition ◽  
The One ◽  
Energy Converting

The term "detonability" with respect to fuel-air mixtures (FAMs) implies the ability of a reactive mixture of a given composition to support the propagation of a stationary detonation wave in various thermodynamic and gasdynamic conditions. The detonability of FAMs, on the one hand, determines their explosion hazards during storage, transportation, and use in various sectors of the economy and, on the other hand, the possibility of their practical application in advanced energy-converting devices operating on detonative pressure gain combustion.

DEFLAGRATION-TO-DETONATION TRANSITION IN A STRATIFIED SYSTEM “GASEOUS OXYGEN-LIQUID FILM OF N-DECANE”

2020 ◽  
Author(s):  
S. M. FROLOV ◽  
◽  
V. S. AKSENOV ◽  
I. O. SHAMSHIN ◽  
◽  
...  
Keyword(s):  
Liquid Film ◽  
Ignition Source ◽  
Gaseous Oxygen ◽  
Deflagration To Detonation Transition ◽  
Operation Process ◽  
Continuous Detonation ◽  
Smooth Channel ◽  
Detonation Transition ◽  
Run Up ◽  
X 24

Deflagration-to-detonation transition (DDT) in the system “gaseous oxygen- liquid film of n-decane” ' with a weak ignition source was obtained experimentally. In a series of experiments with ignition by an exploding wire that generates a weak primary shock wave (SW) with a Mach number ranging from 1.03 to 1.4, the DDT with the detonation run-up distances 1 to 4 m from the ignition source and run-up time 3 ms to 1.7 s after ignition was observed in a straight smooth channel of rectangular 54 x 24-millimeter cross section, 3 and 6 m in length with one open end. The DDT is obtained for relatively thick films with a thickness of 0. 3-0.5 mm, which corresponds to very high values of the overall fuel-to-oxygen equivalence ratios of 20-40. The registered velocity of the detonation wave (DW) was 1400-1700 m/s. In a number of experiments, a high-velocity quasi-stationary detonation-like combustion front was recorded running at an average velocity of 700-1100 m/s. Its structure includes the leading SW followed by the reaction zone with a time delay of 90 to 190 s. The obtained results are important for the organization of the operation process in advanced continuous-detonation and pulsed-detonation combustors of rocket and air-breathing engines with the supply of liquid fuel in the form of a wall film.

Flame Speed and Deflagration-Detonation Analysis in Flare Stack and Header

2018 ◽  
Author(s):  
Philip Diwakar ◽  
Jaleel Valappil
Keyword(s):  
Ambient Air ◽  
Flame Speed ◽  
Safety Concerns ◽  
Deflagration To Detonation Transition ◽  
Detonation Transition

This paper examines safety concerns related to flame speeds when warm relief gas snuffs out the pilot at the flare stack and pulls in ambient air and a spark ignites the vapor in the header. The flame speed essentially determines if the propagating flame speed is a deflagration or a detonation based on whether its subsonic or supersonic. While pipes are sized for deflagrations, they need to be analyzed and tested for detonation pressures and temperatures. Transient CFD calculations help determine the flame speeds, deflagration to detonation transition, pressures and temperatures are compared to pipe specifications and help determine if a detonation leads to a Loss of Containment and suggests mitigations.

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