Overpressure Peak Value Research Articles

Effect of Variable Cross-section Duct on Flame Propagation Characteristics of Premixed hydrogen/methane/air Combustible Gas

ABSTRACT To study the effects of variable cross-section ducts with different configurations on the flame structure, flame propagation speed and overpressure of hydrogen/methane/air premixed gases, a series of experiments were carried out on stoichiometric hydrogen/methane/air mixtures with six hydrogen contents (φ = 0, 10%, 20%, 30%, 40% and 50%). The flame propagates to a distance of 500mm from the ignition end, the sudden change in the cross-section area of the Initially Contracted Cross-Section duct and Centrally Contracted Cross-Section duct will disturb the flame front, the flame only experiences two stages: spherical and finger-shaped. At the sudden change in the cross-section, the smooth flame front folds and forms a turbulent flame. “Tulip” flames can be observed in the Finally Contracted Cross-Section duct and Uniform Cross-Section duct, but the “tulip” flame in the Finally Contracted Cross-Section duct will disappear due to the sudden change of cross-section area of the duct. The flame propagation speed and overpressure increase with increasing hydrogen content. When the flame passes through the sudden change position of the cross-section of the duct, the difference in speed becomes more significant. The shape of the pressure curve varies and pressure oscillation will occurs with the location of a small cross-section tube. Under the same hydrogen content, the overpressure peak value of the duct with Centrally Contracted Cross-Section is the highest, and the overpressure peak value is the lowest when the duct cross-section is uniform.

Experimental study on the explosion-propagation law of coal dust with different moisture contents induced by methane explosion

This study aimed to explore the explosion-propagation law of coal dust with different moisture contents induced by methane explosion. An experimental system of explosion of mixed gas–coal and dust in a straight pipe was established in our laboratory. The evolution of overpressure and the flame-propagation law of deposited-coal-dust explosion with different moisture contents were then studied. Experimental results indicate that when the moisture content is less than 15.12%, the deposited coal dust in the pipeline explodes under the induction of gas explosion. Meanwhile, the total amount of deposited coal dust in the pipeline remains constant; the overpressure peak value and flame-propagation velocity after coal-dust explosion initially increase and then decrease with increased coal-dust moisture content. When the moisture content of the deposited coal dust is 9.57%, the overpressure and flame-propagation velocity of the depositional coal-dust explosion reach the maximum values of 0.766 MPa and 468.553 m/s, respectively. However, when the moisture content exceeds 20.28%, coal dust cannot induce an explosion, and the deposited coal dust can resist a gas explosion. Overall, this research provides theoretical references for methane-induced coal-dust-explosion resistance in coal mines.

Study of autoclaved aerated concrete masonry walls under vented gas explosions

A total of nine full-scale in-situ tests were carried out to investigate the performances of autoclaved aerated concrete (AAC) masonry walls subjected to vented gas explosions. The testing data including overpressure time histories of vented gas explosions, displacement time histories, and damage characteristics of AAC masonry walls in each test were recorded and analysed. It was found that the responses of masonry walls mainly depend on the peak value of overpressure and couple with the time history of gas explosion loads. Typical one-way or two-way flexural mode dominates the failure of AAC walls under vented gas explosions. A detailed micro model for masonry walls was developed in LS-DYNA, incorporating material parameters that were obtained from material tests. The accuracy of numerical model in predicting the responses of masonry walls was verified with the testing data. Parametric studies were conducted to explore the influences of block strength, boundary condition and wall thickness on the performances of masonry walls. The results reveal both wall thickness and boundary condition have significant influences on the response of the masonry wall while block strength has limited effect on its performance. The testing data were compared with the analytical predictions by using design code UFC 3-340-2 and equivalent single-degree-of-freedom (SDOF) methods developed respectively by Biggs and Morison. The results indicate that these predictions on one-way specimens agree well with the testing data, while the performance of two-way specimens is overestimated by using these three methods.

Experimental and numerical study of unreinforced clay brick masonry walls subjected to vented gas explosions

A total of 16 full-scale in-situ tests were carried out to investigate the performances of unreinforced clay brick masonry walls subjected to vented gas explosions. The pressure-time histories of vented gas explosions, displacement-time histories and failure modes of wall specimens in each test were recorded and analyzed. A detailed micro model for masonry wall was developed in the finite element software LS_DYNA 971. The numerical model was validated with the test data and intensive numerical simulations were conducted to explore the influences of boundary condition, bonding pattern and thickness of masonry walls on their performances against vented gas explosions. The results show that the classical yield-line modes dominate failure patterns of masonry walls subjected to vented gas explosions and the dynamic responses of masonry walls are determined by the peak value of overpressure. It is found that boundary condition and wall thickness have great influence on the performance of masonry walls, while bonding pattern has relatively limited influence on its performance. In addition, the recorded gas explosion loads were compared with the predictions from the conventional TNT equivalency method and the methods specified in NFPA 68 and EN 14994. The results indicate both NFPA 68 and EN 14994 approaches give very conservative predictions of peak pressure from gas explosions. The TNT equivalency method also overestimates the peak pressure and predicts a load profile which is significantly different from the test data.

Study of the Similarities in Scale Models of a Single-Layer Spherical Lattice Shell Structure under the Effect of Internal Explosion

The similarity of each scale model is verified based on the theory of similarity, deriving the similarity law of internal explosions in a single-layer spherical lattice shell structure via dimensional theory, calculated based on models with scaling coefficients of 1, 0.8, 0.6, 0.4, 0.2, and 0.1. The results show that the shock wave propagation characteristics, the distribution of the overpressure on the inner surface, the maximum dynamic response position, and the position at which the earliest explosion venting occurs are all similar to those of the original model. With the decrease of scaling coefficients, the overpressure peak value of the shock waves of each scale model, and the specific action time of the positive pressure zone, as well as specific impulse are increasingly deviated from the original model values; when the scaling coefficient is 0.1, the maximum relative error between the overpressure peak value at the measurement point and the specific action time of the positive pressure zone as well as the specific impulse and the original model value is 4.9%. Thus, it is feasible to forecast the internal explosion effect of the original structure size model by using the experiment results of the scale model with scaling coefficient λ≥0.1.

Online Correction of the Dynamic Errors in a Stored Overpressure Measurement System

The problem encountered in sharp shock testing as a result of inadequate bandwidth must be addressed to obtain an accurate overpressure peak value when measuring the steep signals of shockwaves during explosions. A dynamic compensator can effectively amend the dynamic errors caused by sensor system characteristics; thus, a dynamic compensation method based on improved particle swarm optimization (PSO) algorithm is proposed in this paper. This method can effectively overcome the influence of the initial value derived with PSO algorithm on compensator index. The distributed algorithm is introduced into the hardware structure design of the dynamic compensator to facilitate the application of an optimized compensator to real-time online measurement. This integration realizes the high-speed parallel of the dynamic compensator of the sensor with field-programmable gate array. Experimental results show that a high-speed parallel dynamic compensator can amend the dynamic errors in a sensor accurately and in a timely manner.

Vacuum chamber suppression of gas-explosion propagation in a tunnel

Abstract To control and reduce the harm of a gas explosion, a new method is proposed for suppressing gas-explosion propagation in a tunnel by using a vacuum chamber. We studied the suppression effect on gas explosions by placing a vacuum chamber at different positions along the tunnel. The results indicate that: 1) the vacuum chamber can absorb the explosion wave and explosion energy as much as possible at the beginning of the gas explosion, and; 2) when the vacuum chamber is used the closer it is to the ignition source the more significant the suppression effect. In addition, by using the vacuum chamber: 1) the flame propagation velocity decreases from ultrasonic to subsonic; 2) the flame propagation distance is remarkably shortened; 3) the maximum peak value of overpressure (pm) decreases from 0.34 to 0.17 MPa or less, and; 4) the impulse of the blast wave (I decreases from 20 to 8 kPa·s or less.