| Many countries around the world are now racing to develop low-thrust liquid rocket engines with high specific impulse,compact structure,environmental friendliness and low cost.On this background,the spray and electric ignition characteristics of HAN-based liquid propellants in a small scale space are studied.The main research contents and results are as follows:(1)For simulation HAN-based liquid propellants,the spray parameters under an unlike impinging nozzle in atmospheric environment and in a simulation chamber were tested by using of Particle Dynamic Analyzer(PDA)respectively.The results indicate that,the greater the nozzle pressure is,the smaller the droplets' Sauter mean diameter(D32)is.The droplets'diameter fluctuates greatly near the nozzle,and it becomes gentle downstream.The circumferential distribution of the droplets' axial velocity displays two peaks.The peaks appear at ?=90° and a=270°,respectively.The droplets' axial velocity and radial velocity decrease as the distance between the measurement point and the center axis increases.The further away from the nozzle,the lower the axial velocity and radial velocity.D32 in the simulation chamber is larger than that in atmosphere environment,and normal distribution of D32 is clearer.The droplets' axial velocity in the simulation chamber is closed to that in atmosphere environment.However,the simulation chamber has greater impact to the droplets'radial velocity.(2)An inverse doubt-swirl air-assist nozzle was designed.The distribution characteristics of the spray parameters for the nozzle in atmospheric environment and in the simulation chamber were tested with PDA system.The results show that D32 fluctuates along the center axis,and then its distribution becomes uniform.The further the measurement point from the center axis,the larger D32.D32 in the simulation chamber has a larger fluctuation in the circumferential distribution.When the liquid pressure is constant and the gas pressure improves,D32 decreases and the axial velocity increases.When the gas pressure is constant and the liquid pressure improves,D32 increases while the axial velocity changes slightly.(3)Based on the experiment of the unlike impinging nozzle,a two-dimensional unsteady spray model was built,and numerical simulations were conducted.The results show that the spray angle forms after two jets impinge.The vertex is the impinging point.The spray presents a cone shape with mass discrete droplets at the edge.Due to the limit of the wall,the amount of the discrete droplets in the simulation chamber is more than that in atmospheric environment.The greater the nozzle pressure,the smaller D32 and the higher the axial velocity.The bigger the impinging angle,the smaller D32 and the axial velocity.A higher liquid viscosity leads to larger D32 and lower axial velocity.The simulation results agree well with the experimental data.The maximum deviation error is 8.19%.(4)Based on the experiment of the inverse doubt-swirl air-assist nozzle,a three-dimensional unsteady spray model was built,and numerical simulations were conducted.The results indicate that,the spray field spreads in the shape of a cone.Its flow field is very complex with several co-existence vortices.In the simulation chamber,the shape of the spray is a cone at first,then turns to be fusiform after it hits the wall.The flow field in the simulation chamber is symmetric.When the liquid pressure maintains at 0.2MPa and the gas pressure improves,D32 decreases and the axial velocity increases.When the gas pressure is higher than 0.45MPa,further improvement of the gas pressure has little effect on D32.When the gas pressure maintains at 0.35MPa and the liquid pressure improves,D32 increases while the axial velocity changes slightly.As the liquid viscosity increases,D32 increases while the axial velocity decreases.(5)An experimental system was conducted in order to study the electrical ignition characters of HAN-based liquid propellant droplet(LP1846)in atmospheric environment.Base on the experiment,a two-dimensional unsteady droplet ignition model was set up.Results show that,under the linear voltage,the droplet will firstly vaporize and decompose on heating,then catch fire.In the ignition process,the current through the droplet first increases and then decreases.The greater the voltage,the higher the peak value of the current and the earlier the peak appears.According to the variation of reaction rate and temperature,the electrical ignition process can be distributed into three characteristic stages:preheating,thermal decomposition and combustion.In corresponding stages,LP1846 droplet turns from spherical to umbrella until it burns out.The ignition delay time decreases with the increasing of the maximum voltage.(6)An annular sequence pulse electrical igniter was designed.The electrical ignition experiment was carried out.Base on the experiment,a three-dimensional unsteady model was built to simulate the spray ignition and combustion process.A numerical prediction on the working process of a simulation thrust chamber with the annular sequence pulse electrical igniter was carried out.Results show that the simulation is consistent with experimental result.The igniter can preferably achieve multi-point ignition to improve ignition reliability of LP1846 spray.After the ignition starts,the separation flames will merge into one.The flame structure is a hollow cone.The ignition area increases while the rotation speed of the electrode increases.Stronger discharge voltage will improve the volume and temperature of the sparks.The amount of the flames increases significantly that is beneficial to spray ignition.In the simulation thrust chamber,the improvement of the discharge voltage and the rotation speed of the electrode will all improve the thrust peak in start-up process and make it appear earlier.The greater the gas pressure,the higher the value of the thrust peak and the shorter the time of start-up process.The value of the thrust in start-up and normal process increases while the liquid pressure increases. |
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