This review examines existing knowledge on the genesis and flame acceleration of explosions from methane–air mixtures. Explosion phases including deflagration and detonation and the transition from deflagration to detonation have been discussed. The influence of various obstacles and geometries on explosions in an underground mine and duct have been examined. The discussion, presented here, leads the readers to understand the considerations which must be accounted for in order to obviate and/or mitigate any accidental explosion originating from methane–air systems.

A review on understanding explosions from methane-air mixture

Temperature and pressure influence on explosion pressures of closed vessel propane-air deflagrations.

Hydrogen-enrichment has been proposed as a useful method to overcome drawbacks (local flame extinction, combustion instabilities, lower power output, etc.) associated to turbulent premixed combustion of natural gas in both stationary and mobile systems. For the safe use of hydrogen-enriched hydrocarbon fuels, explosion data are needed. In this work, a comparative experimental study of the explosion behavior of stoichiometric hydrogen-enriched methane/air (with 10% of hydrogen molar content in the fuel) and pure methane/air mixtures is presented. Tests were carried out in a 5 l closed cylindrical vessel at different initial pressures (1, 3 and 6 bar), and starting from both quiescent and turbulent conditions. Results allow quantifying the combined effects of hydrogen substitution to methane, pressure and turbulence on maximum pressure, maximum rate of pressure rise, burning velocity and Markstein lengths.

Combined effects of initial pressure and turbulence on explosions of hydrogen-enriched methane/air mixtures

Explosion of gaseous ethylene–air mixtures in closed cylindrical vessels with central ignition

The rate of pressure rise of gaseous propylene–air explosions in spherical and cylindrical enclosures

The paper outlines an experimental study of influence of the ignition position and obstacles on explosion development in premixed methane–air mixtures in an elongated explosion vessel. As the explosion vessel, 1325 mm length tube with 128.5 mm diameter was used. Location of the ignition was changeable, i.e., fitted in the centre or at one of ends of the tube, when the tube was in a horizontal position. When it was in a vertical position, three locations of the ignition (bottom, centre and top) were used. In the performed study, the influence of obstacles on the course of pressure was investigated. Two identical steel grids were used as the obstacles. They were placed 405 mm from either end of the tube. Their blockage ratio (grid area to tube cross-section area) was determined as 0.33 for most of experiments. A few additional experiments (with smaller blockage ratio—0.16) were also conducted in order to compare the influence of the blockage ratio on the explosion development. Also some experiments were conducted in a semi-cylindrical vessel with volume close to 40 l. All the experiments were performed under stabilized conditions, with the temperature and pressure inside the vessel settled to room values and controlled by means of electronic devices. The pressure–time profiles from two transducers placed in the centreline of the inner wall of the explosion vessel were obtained for stoichiometric (9.5%), lean (7%) and rich (12%) methane–air mixture. The results obtained in the study, including maximum pressures and pressure–time profiles, illustrate a quite distinct influence of the above listed factors upon the explosion characteristics. The effect of ignition position, obstacles location and their BR parameters is discussed. The additional aim of the performed experiments was to find the data necessary to validate a new computer code, developed to calculate an explosion hazard in industrial installations.

Influence of ignition position and obstacles on explosion development in methane–air mixture in closed vessels

The experimental results of the measurements of the explosion pressure and rate of explosion pressure rise as a function of molar methane concentration in the mixture with air in the 40 dm3 explosion chamber are presented. The research was aimed at determination of the explosion limits, according to the EU Standard. The influence of initial temperature of the mixture (changing in the range of 293–473 K) on the fundamental explosion parameters was also investigated. The ignition source was an induction electrical spark of the power equal to approximately 10 W. It was stated, that the increase of initial temperature of the methane-air mixture causes a significant increase of the explosion range.

Determination of explosion parameters of methane-air mixtures in the chamber of 40 dm3 at normal and elevated temperature

Gaseous and dust (including hybrid) explosions often occur in mines, grain elevators, and industrial plants, and always lead to severe damage. Strategies for suppressing or mitigating explosions are developed based on an understanding of their physical mechanism. This study briefly summarized previous studies on explosions, detonations, and the deflagration-to-detonation transition (DDT), and then discussed potential passive/active or hybrid methods for suppressing explosions and detonation in tubes and galleries. Suppression can be achieved using methods that are focused on eliminating or mitigating factors that can either promote the reactive process or break down the DDT process. These methods involve lowering temperature and pressure, diluting the mixture concentration, and venting the closed system. The method of tuning wall materials (using aerogel) is also validated for the effectiveness of detonation suppression. By using various sensors to detect propagating flames or pressure increases in tubes or galleries, active systems can disperse a suppressing agent to extinguish combustion in a timely manner. It is commonly regarded that the active systems are superior to passive methods that operate without additional control units in some ways, but there are always limitations on the application due to reasons such as the cost of equipment, regular maintenance as well as reliability of the complicated integrated-systems. Practice applications show that there is no method of explosion prevention is absolutely safe. In reality, people must consider various factors in the development of an explosion/detonation suppression system to reduce the risk to an acceptable level.

Grzegorz Rarata

Papers

Influence of ignition position and obstacles on explosion development in methane–air mixture in closed vessels

Determination of explosion parameters of methane-air mixtures in the chamber of 40 dm3 at normal and elevated temperature

Brief review on passive and active methods for explosion and detonation suppression in tubes and galleries

Development of the ILR-33 “Amber” sounding rocket for microgravity experimentation

Performance evaluation of the hypergolic green propellants based on the HTP for a future next generation spacecrafts