Study of explosion physics

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The increase in the consumption of fossil fuels for power production has led to a measured rise in the atmospheric concentration of the greenhouse gas carbon dioxide. The use of higher-hydrogen content gaseous fuel in gas turbines and internal combustion engines for fixed power generation has been promoted in order to reduce the production of carbon dioxide, a byproduct of burning carbon based fuel. The explosion hazard associated with these fuels is significantly higher than that for natural gas currently used in power plants. A method to categorize the relative hazard associated with these new high hydrogen content fuels is required for safety guidelines. In fact, a better system is required to categorize common fuels used in the chemical industry and transported by rail and trucks. This is important to mitigate major incidents like the explosion caused by the train derailment in Lac-Megantic, Quebec, on July 6, 2013 that killed 35 people. The National Fire Protection Agency recommends the use of the minimum explosion safe gap (MESG) to design explosion-proof electric equipment, such as electric motors. The smaller the fuel-air mixture’s MESG, the more hazardous the fuel. Because of the small scale of the apparatus used to measure the MESG, experiments are relatively inexpensive to perform, and as a result data exists for a wide range of fuels. The MESG is useful for describing fuel-air mixture sensitivity to flame propagation, however, it is not an appropriate parameter to characterize the sensitivity of such a mixture to detonate. A detonation is a supersonic combustion wave that propagates by a process that is different from that of a flame. The experimentally measured detonation cell size is generally used to characterize detonation sensitivity of a gas, but the ±50% measurement uncertainty is not acceptable for safety guidelines. Another parameter that could be used is the critical tube diameter but it requires a relatively large apparatus that makes it impractical for obtaining data for a large number of fuels. A method is proposed to measure the sensitivity of a fuel to detonate based on the propagation of a supersonic combustion wave through a tube equipped with a series of orifice plates. The minimum (or critical) orifice plate diameter that can support the propagation of a combustion wave propagating at an average velocity faster than the theoretical highest flame velocity will be measured for different fuel-air mixtures. Much like the MESG, the smaller the critical orifice plate diameter the more detonable the mixture. Experiments will be performed to investigate supersonic combustion wave propagation. The critical orifice diameter will be measured for different fuels in a round steel tube. Experiments are performed with a fuel-air mixture where the orifice plate diameter is progressively increased until a supersonic combustion wave can propagate. Another experiment will be carried out in a channel where high-speed video will capture the structure of the combustion wave as it propagates past a series of obstacles. The visualization results, along with computational fluid dynamics modeling, will make possible the identification of the physics involved in the way a supersonic combustion wave propagates in an obstacle laden tube. This experimental program will provide data for the development of safety guidelines to be used for the transport and use of common fuels. Such guidelines have the potential to limit the number of severe accidental explosions, thereby minimize property and environmental damage, and ultimately prevent the loss of life. This program will provide training of multiple highly qualified personnel, including one MASc, two PhDs, and five undergraduate students.