Experiment on the measurement of combustible gas combustion parameters

Experimental purpose 1. Deepen the understanding of basic concepts such as the explosive limit concentration of combustible gas and the flame propagation speed of combustible gas, understand the structure of combustible gas flame, understand the mechanism and characteristics of premixed gas flame propagation, and master the resistance of metal mesh flame arresters The principle of fire explosion isolation; 　　2. Master the method of measuring the explosion limit and flame propagation speed and other parameters.　　　　Experimental principle 　　When the mixture of combustible gas and air burns when it encounters a fire source, it will generate a lot of heat, which will cause the product to heat up, increase in temperature, and expand in volume. It will explode when the combustion is violent. Whether the mixed gas composed of combustible gas and air can explode in contact with a fire source is closely related to the concentration of combustible gas in the mixed gas. Only the combustible gas whose concentration is within the explosive limit concentration range will explode in the air. The so-called explosion limit refers to the highest or lowest concentration of combustible gas (expressed in volume percentage) that a mixture of combustible gas and air can explode when exposed to a fire source. The lowest concentration is called the lower explosion limit; the highest concentration is called the upper explosion limit. The reason for the explosive limit of combustible gas is that if the concentration of combustible gas is lower than the lower explosive limit concentration, the excess air has a strong cooling effect and the effect of destroying free radicals, making it difficult for explosive reactions; if the concentration of combustible gas is higher than the upper explosive limit concentration , Insufficient air suppresses the explosive reaction. When the concentration of combustible gas is near the stoichiometric concentration, the effect that is not conducive to the explosive reaction is the smallest, and the explosion is the most prone to occur and the most violent. The explosive limit of flammable mixtures can be approximated by empirical formulas, or can be determined by experimental methods.　　The flame (ie combustion wave) propagates in the premixed gas. According to the theory of gas dynamics, it can be proved that there are two modes of propagation: normal flame propagation (deflagration) and detonation. The normal flame propagation mainly relies on the effect of heat transfer (heat conduction), which transfers the combustion heat in the flame to the unburned gas, which heats it up and ignites, so that the combustion wave propagates in the unburned gas; the detonation mainly relies on the high pressure effect of the shock wave. The phenomenon that the unburned gas is heated and ignited under the condition of approximately adiabatic compression, so that the combustion wave propagates in the unburned gas.　　 After ignition, whether the flammable mixture in the pipeline undergoes normal flame propagation or explosion (or even detonation) depends on many factors. Through experiments, it is found that the ignition in the detonation tube is easy to achieve an explosion, and the normal flame propagation can be obtained when ignited at the opening of the detonation tube; the combustible mixture in the short pipe is not easy to achieve detonation, and if the pipe is long enough, The combustible gas mixture will eventually achieve detonation; in a shorter pipeline, the turbulence intensity of the combustible gas mixture can be enhanced by adding baffles, etc., to achieve detonation.　　 When the flame propagates in a pipe full of combustible gas, the flame propagation speed will be affected by the heat dissipation of the pipe wall and the destruction of free radicals in the flame on the pipe wall. It is precisely because the flame arrestor can enhance the heat dissipation of the pipe wall and the destruction speed of free radicals on the solid phase, and play a role in preventing fire and explosion. Therefore, a flame arrestor is added to the combustible gas circulation pipeline that may burn or explode. To cut off the spread of burning or explosive flames. Generally used between high-heat equipment, combustion chambers, high-temperature oxidation furnaces, high-temperature reactors, etc. and pipelines that transport combustible gas and flammable liquid vapor, as well as containers, pipes, and equipment exhaust pipes for flammable liquids and combustible gases. The flame arrester is used to arrest the fire. Flame arresters generally use multi-layer metal meshes as flame-extinguishing elements. Such flame arresters are called metal mesh flame arresters. Flame suppression elements can also be composed of perforated plates, corrugated metal plates, and fine-grained packing layers. When using the flame arrester, it should be checked and repaired frequently to prevent the holes from being blocked and causing poor gas transmission, or being corroded and damaging the flame suppression components.　　 The fire and explosion-proof effect of the metal mesh flame arrester is affected by many factors, mainly including: metal mesh material, mesh number and number of layers, etc. Experiments have found that the fire-proof and explosion-proof effect of metal mesh with large thermal conductivity is better than that of metal mesh with low thermal conductivity; the fire-proof and explosion-proof effect of metal mesh with large mesh is better than that of metal mesh with smaller mesh of the same material. Good explosion-proof effect; multi-layer metal mesh has better fire and explosion-proof effect than single-layer metal mesh, but large-mesh metal mesh and multi-layer metal mesh will significantly increase the flow resistance of airflow.