Mechanism Study Of The Detonation Phenomenon And The Stable Combustion Control Of The Combustion Light Gas Gun

The interior ballistics of the Combustion Light Gas Gun(CLGG)is a typical premixed flame propagation process in confined space.High pressure loading of the hydrogen-oxygen propellant makes the combustion intense and easily to become unstable through the coupling enhancement with the stochastic shocks,which may even lead to deflagration to detonation transition(DDT)phenomenon and causing serious safety hazard to the combustion device.In order to master the interior ballistics characteristics and laws of CLGG,1D and 2D flow combustion models with detailed reaction mechanism were firstly build in this dissertation.Then a series of numerical studies were carried out to reveal the key principles of the interior ballistics,including the confined high-pressure hydrogen-oxygen flame acceleration dynamics,the multipoint flame interaction,the DDT phenomenon,and the stable combustion control techniques.The main content and innovations of this dissertation includes:Firstly,a 1D interior ballistics model was built by making proper assumptions on the hydrogen-oxygen combustion process,a numerical program was then compiled for solving the governing equations following the principles of the WAF-HLLC Riemann solver theory,which provides a fast analysis measure for the interior ballistics research.Flame propagation under different hydrogen-oxygen equivalence ratios were simulated,and it was found the propagation process can be separated into three distinctive stages,which are initial exponential acceleration,fast deflagration and end-gas deceleration.1-D DDT occurs only when the synchronized propagation and enhancement feedback is established between the flame surface and the shockwave at high speed deflagration stage.Detonation will bring a slight increase on the muzzle velocity,but will also cause a high intensity shock and the following high amplitude pressure oscillation.Besides,the relationship between the flame propagation distance and the DDT triggering spatial-temporal characteristics is also analyzed.Research of this section provides a basic and preliminary study method for the interior ballistics of CLGG.An axisymmetrical 2D LES model with detailed reaction mechanism was built and solved by applying the Artificial Thicken Flame(ATF)approach and the Adaptive Mesh Refinement(AMR)method.Typical dynamic stages of the spherical flame,finger flame,flat flame and the end-gas combustion are recorded for the profound revealing of the H2-O2 flame propagation mechanism.It was found the flame surface increasing is the dominant mechanism for the exponential acceleration in the spherical stage and the early finger flame stage.This mechanism fails as a result of the no longer increasing surface when the flame skirt reaches the wall and the unburnt gas compression resistance established at high speed deflagration.The weak acceleration of the deflagration flame is promoted by the positive feedback established among the pressure wave,the turbulence,and the reaction heat release.Flame decreases sharply with flame structure degenerates into a flat shape when propagates closing toward the bullet,which is due to the restrained movement of the unburnt gas.The following end-gas flame propagation is dominated by the Richtmyer-Meshkov instability,which creates a bubble flame firstly through the shock-flame interaction,and then continues propagating radially under the vortex diffusion dynamics.Typical spike-bubble structures were observed as a result of the shockwaves passing through the flame surface.Research for the multi-point flame interaction was conducted,it was found that the interaction is mainly circumscribed between two adjacent flames,and the axial acoustic oscillation is the main cause for the flame structure distortion.Research of this section clarified the flame propagation principles and the inner dynamics for the normal interior ballistics of CLGG.Simulation results of the DDT process under various conditions were sorted and analyzed.The transition mechanism is revealed by analyzing the coupling enhancement between the shock waves and the flame,which is the key of the event trigger.Simulation results indicate that there are two types of the DDT transition mechanisms.The first is the synchronized propagation and enhancement feedback established between a chocked high-speed flame and the shockwave inside the reaction region,while the second is the local explosion rising from a "hot-spot" nearby the flame surface.It was also found that the hot-spot induced DDT can be separated by two ways.One is achieved by the trigger shock passing through the flame surface from the inside burnt region to the unburnt region,the trigger mechanism is the strengthening and accelerating mechanism as a result of the overlapped trigger shock,attaching shock inside the reaction zone,and reaction heat release;while the other one is achieved by creating a DDT induction time gradient,which can be realized by shock confluence.Besides,DDT is observed being triggered at spherical stage in a high intense reaction situation,forming simultaneous multiple hot-spot induced DDTs.Research also found a special DDT phenomenon during the end-gas propagation stage,when the flame speed is low.The trigger mechanism is the directly ignited local explosion by shock focusing in the fully compressed and heated unburnt gas.Research of this section reveals the formation mechanism of most DDT occasions in CLGG,and enlightens the direction for the stable combustion research.Several ways were studied to achieve stable combustion interior ballistics in CLGG and avoid the detonation hazard.The effect of the obstacle on the flame propagation was firstly studied,and the DDT mechanism was concluded.Simulation results indicate a negative effect on the stable control as a result of the earlier and shorter shifted DDT trigger time and travel distance.A membrane breaking explosion ignition tube was then designed and introduced into the ignition of the hydrogen-oxygen propellant.The propagation dynamics of the jetting flame was studied,and the influence of the breaking pressure and the diameter of the vent holes on the flame propagation was evaluated.Simulation results indicates that this ignition method will provide effective suppression on the DDT phenomenon,create fewer high-amplitude pressure oscillations,and make the bullet accelerates smoother.