Research On Unsteady Propagation Of Detonation Wave Near Failure Condition

Combustible gas is widely used in the field of petrochemical, mining and gas supply. However, once the combustible gas explodes, it will cause severe damage of people’s lives and property. The investigation of unsteady propagation of detonation wave in tubes is very significant to the work of explosion prevention and suppression. Characteristics of unsteady propagation of detonation wave near failure in tubes are studied using the experimental and theoretical analysis method, which can provide an experimental and theoretical basis for the prevention of explosion hazards of combustible gas. The main work and conclusions are as follows.(1) The characteristics of detonation velocity are investigated when detonation propagating along the tubes. When the initial pressure of mixture is much higher than the limiting pressure of detonation failure, the detonation wave propagates at a stable mode in both round tubes and annular channels. With decreasing the initial pressure, the fluctuation of detonation local velocity increases and the detonation wave propagates at rapid fluctuation mode. However, for the1.5mm,3.2mm and12.7mm diameter tubes, the fluctuations of detonation local velocity for unstable mixtures are very large and the propagation modes of stuttering, galloping and low-velocity detonation occur. When the initial pressure is lower than the limiting pressure of detonation failure, the detonation velocity will decay and fail completely after a short distance propagation in the round tubes and annular channels.(2) The detonation velocity deficit near failure is studied. The effect of composition of mixture, initial pressure, and tube dimension on the velocity deficit is performed. The boundary layer of the wall will cause the energy loss of detonation wave when detonation wave propagates along the tube. The energy loss leads to the velocity deficit when detonation wave propagates along the tube. The maximum value of velocity deficit is of about30%VcJ. The Fay model is modified, and is applied to the annular channel. The prediction results agree well with the experiment results, and the maximum relative error is less than8%.(3) The variation of cellular structure of detonation wave is investigated. When the initial pressure of mixture is much higher than the limiting pressure of detonation failure, the detonation wave has a multi-headed cellular structure. As the initial pressure decreasing towards to the limiting pressure of detonation failure, single headed spinning detonation wave occurs. Under the propagation mode of galloping detonation, the cellular structure of detonation goes through three different phases, which are attenuation, disappearance and re-formation. When the initial pressure is lower than the limiting pressure of detonation failure, the cell size of cellular structure will increase gradually and disappear after a short distance propagation, which confirms that the detonation wave fails completely.(4) The disappearance of single headed spinning detonation is characterized as the onset of detonation failure for detonation wave of stable mixtures, and detonation wave of unstable mixtures in50,8mm diameter tube. Also, the disappearance of single headed spinning detonation is characterized as the onset of detonation failure for detonation wave of both stable and unstable mixtures in annular channels. However, for the smaller diameter tubes, like D=1.5mm,3.2mm and12.7mm, the disappearance of galloping detonation and low-velocity detonation is characterized as the onset of detonation failure. The propagation characteristics of single headed spinning detonation and galloping detonation are investigated. For single headed spinning detonation and galloping detonation, there exists a pressure range under which the single headed spinning detonation and galloping detonation occur. The pressure range decreases with the initial pressure. For galloping detonation, it is found that the instability plays an important role in the formation of galloping detonation.