Investigation On The Characteristics Of Flame Propagation And Direct Initiation Of Detonation For Combustible Gas

With the rapid development of industrialization, energy from burning combustible gas has become a major source of heat supply and power output. Fuel burning provides energy for human life as well as fires and explosions, and causes heavy casualties and property losses. Laminar combustion and detonation of gaseous fuel are two stable states for the low-speed and high-speed fuel burning. Their characteristic parameters of combustion are important basis to reflect the essential characteristics of the fuel. In this thesis, a series of experiments were conducted to study propagation characteristics of laminar flame and direct initiation of detonation with self-developed ignition systems and explosion test system. The results of these experiaments provided basic data for flame propagation and direct initiation of detonation. The mechanisms of flame instability and detonation formation were discussed by summary of the laws and theoretical analysis, which provided theoretical support for a safe and efficient utilization of gas fuel and fire and explosion prevention.A new electrostatic ignition device for kilojoules energy is designed according to the actual needs. The spark discharge characteristics and the laws of energy released are studied by using the test platform. A new method of computing the spark energy by integration spark resistance and loop current is proposed. Using this method a series of calculation and calibration on spark energy are achieved for different stalls of ignition device, which provide the technical supports to study flame propagation and direct initiation of detonation.The effect of spark discharge on ignition process in gas mixture is studied experimentally, and the range of impact on the flame propagation by ignition energy is analyzed in process of the small energy ignition. Meanwhile, the range of valid data in laminar burning velocity measurement experiment is determined. Through the using of near-field test platform and detonation pressure experiments, the formation and propagation of the blast wave induced by spark discharge are studied, the calculation method of the blast wave energy is proposed. By this method, the blast wave efficient energy in high energy ignition stalls is calibrated. These research results can be sued to determine the efficient initiation energy in direct initiation of detonation by high energy spark discharge.According to the ignition and flame propagation characteristics of the gas, the combustion and explosion test system is designed, and the laminar burning velocity of premixed gas and Markstein length are obtained. The laminar flame propagation characteristics of propane/air, hydrogen/air and ammonia/air mixtures are investigated. Meanwihle the combustion characteristics of hydrogen and ammonia compound fuel/air mixtures are investigated for the first time in China. The laminar burning velocity and the markstein length of different fuel/air mixtures are studied. The instability mechanism of laminar premixed spherical flame is investigatated on the basis of the markstein length and the flame surface properties obtained from schlieren pictures.Using the high energy ignition system and combustible gas explosion experimental system, spherical detonation direct initiation for several typical premixed gas is achieved by blast wave induced by high energy spark discharge in china for the first time. The critical energy of detonation direct initiation for hydrogen/oxygen, propane/oxygen and acetylene/oxygen mixture is measured in different equivalence ratio and initial pressure. The variations of critical initiation energy with initial conditions are studied, and the predicted values of critical energy are compared with the experimental ones. By the schlieren pictures in direct detonation initiation, the detonation velocity and flame structure evolution process are investigated, a new initiation model is proposed to explain the process of detonation direct initiation, and the critical velocity of direct initiation of detonation is determined. Meanwhile, the cellular pattern and the formation mechanism of direct initiation of detonation are studied, and a new basic principle for spherical detonation direct initiation is given.The objective of this thesis is to investigate the characteristics of laminar flame propagation and direct initiation of detonation, which contribute to enrich the data of the combustion and detonation theory. They are useful to gas fire and explosion prevention in industries.