Research On The Safety Characteristics And Deflagration Reaction Mechanism Of Liquid Monopropellant Of Anhydrous Hydrazine-Based

The composition and formula system of liquid propellant are very complicated and there are many stimulating factors that can induce its accidental ignition and explosion.Even under preset working conditions,there is still the possibility of accidental explosion even though various safety measures have been taken.The application and the persistent enrichment of energetic materials in liquid propellants would significantly increase the risks of accidental combustion and explosion.On the other hand,the energy release rate of liquid propellant is greatly affected by the external environmental conditions（package design pressure,reaction scales,etc.）.Under non-predetermined working conditions,the reaction characteristics of liquid propellants may undergo qualitative changes,which was also liable to cause combustion or explosion accidents,which had happened many times over the past few decades.However,at present,liquid propellants are more often managed as dangerous chemicals in China and the safety distances for the production and storage of liquid propellants are mainly based on fire codes,but the serious harm caused by their explosive characteristics is ignored.To evaluate the safety characteristics and detonation effects of liquid propellants,in the study,anhydrous hydrazine-based（anhydrous hydrazine and DT-3）monopropellant propellants were selected as the research objects,and systematically analyzes various sensitive stimulus parameters and threshold ranges that may be encountered during production,storage,transportation and use.Most importantly,the detonation characteristics of large charge FAE and explosive shock wave and thermal damage when exposed to external fire of anhydrous hydrazine and DT-3 were studied.The main work contents are as follows.（1）The thermal response characteristics of anhydrous hydrazine and DT-3 were researched by micro-calorimeter and slow cook-off performance test device.It was confirmed that the phase transition process existed in both of them during heating.The initial decomposition temperature of anhydrous hydrazine was lower than that of DT-3 and the initial decomposition temperature of the substance of the slow heating test was significantly lower than that in the C600 test.Considering safety and practical application,it is considered that it is more suitable to use the slow heating test to clarify the thermal decomposition temperature of the sample.（2）The impact energy finally broke through the bond breaking of anhydrous hydrazine and DT-3 and the reaction energy barrier of anhydrous hydrazine,DT-3/oxygen,and provided energy for the breaking of its own N-N and N-H bonds.The results showed that the critical impact energy of anhydrous hydrazine is below the critical reaction threshold for the impact of DT-3.anhydrous hydrazine was more sensitive to the knock on effect of DT-3.Within25℃～60℃,the temperature had a significant effect on the fall hammer impact sensitivity of anhydrous hydrazine,especially the DT-3.The free water in the DT-3 substance inhibits the energy transfer generated by the discharge capacitance and hinders the firing of anhydrous hydrazine and hydrazine nitrate in the DT-3 component,resulting in a lower electrostatic susceptibility threshold for anhydrous hydrazine than for DT-3.Both anhydrous hydrazine and DT-3 liquid propellants undergo thermal explosion when subjected to continuous high temperature under highly enclosed condition,and DT-3 is more sensitive to the continuous high temperature effect.Shock wave sensitivity test indicated that anhydrous hydrazine could not propagate detonation.Analysis suggests that although anhydrous hydrazine has one N-N high-energy bond,its molecular structure is simple and there is no oxygen.Although the system of DT-3 contains hydrazine nitrate,the content is small and the water in the system reduces the shock wave sensitivity of the system.The contact surface of anhydrous hydrazine,DT-3 and air is also positively small in the test.In addition,the liquid propellant is a homogeneous substance and generally does not generate bubbles inside,which means that there is no“hot spot”conducive to the growth of detonation.Therefore,anhydrous hydrazine could not rapidly undergo an oxidation-reduction reaction and considered to be insensitive to the shock wave.（3）The hazard characteristics of the ignition and explosion reactions of two single component liquid propellants,anhydrous hydrazine and DT-3,were investigated in the event of an accidental steam leak.The experimental parameters of 5 kg and 10 kg fuel cloud scattering were reasonably designed to simulate the distribution of sample vapor in space environment when accidental leakage occurred.The diffusion law of the cloud in 1 ms time period was simulated,and the microscopic motion law of the liquid fuel cloud was obtained.the conclusions were as follows:The average TNT equivalences of 5 kg and 10 kg hydrazine clouds are 1.35 and 1.58,respectively,and They are 6.21 times and 2.08 times of TNT equivalent of the same magnitude DT-3 explosion,respectively.The maximum propagation velocity of the flame generated by the reaction of 10 kg anhydrous hydrazine and DT-3 is about 2246 m·s^-1and 1258 m·s^-1,respectively.Only part of the cloud of the 5 kg DT-3sample participated in the reaction.Obviously,the results show that the mixture system of anhydrous hydrazine and air has an explosion reaction.The cloud detonation intensity of anhydrous hydrazine is significantly stronger than that of DT-3.The quality of the liquid fuel has a significant effect on the explosive TNT equivalence results.Within a certain range,with the increase of mass,the proportion of cloud and mist concentration participating in the detonation reaction increases obviously,and the intensity of detonation also increases with the increase of size effect.In the experiment,the rules of shock wave overpressure and high speed and infrared test results are consistent.The、research results have important guiding significance for the explosion protection of accidental leakage of liquid propellant.（4）The specific reaction path of the mixed system of anhydrous hydrazine and oxygen is discussed and the energy release mechanism of that on the picosecond time scale and nanoscale space scale is also given.The results show that due to the weak interaction,the mixed system of N₂H₄and O_2`aggregates from a dispersed state to form a“droplet”,which increases the collision probability in the sense of the kinetics of the reaction and promotes the deflagration reaction between N₂H₄and O₂.On the other hand,the reaction of N₂H₄with O₂produces a large number of residue fragments such as nitrogen hydrogen,nitrogen oxygen,oxygen hydrogen,etc.that have not been fully released and the residual residues will further release energy in the subsequent reaction process.The corresponding reaction rate is both explosive and also flammable.（5）The explosion effect in case of fire stimulation of anhydrous hydrazine and DT-3 in standard packaging was studied by the combination of experiment and numerical simulation.The results showed that:Under the external fire burning condition,the heating temperature of the packaged liquid propellants was much higher than its thermal decomposition temperature.As a result,the samples contacted with the steel tube decomposed rapidly and hence produced a lot of gas products with high temperature and high pressure.For the storage tank was airtight,the gas volume kept expanding and the vapor pressure increased so fast that the stress generated by the gases exceeded the design pressure of the package,which led to the occurrence of a violent burning and/or explosion.High-speed video results showed that both anhydrous hydrazine and DT-3 exploded first and made the storage tank destroyed,and then the liquid samples in the tank were spilled and atomized into small liquid columns or droplets with the help of the high-pressure reaction products,which quickly evaporated and became gaseous combustibles to be ignited.The final result was that the 18 kg anhydrous hydrazine and the DT-3 standard storage tank had an explosion/detonation reaction,the reaction of DT-3-120 kg storage tank was deflagration,and The response of anhydrous hydrazine-120 kg tank to fire was combustion.Unexpectedly,there was no positive correlation between the shock wave hazard effect and the mass of the sample.The analysis showed that the shock wave effect of sample reaction was related to the design pressure of package.Therefore,within a certain design pressure range,the design pressure of the storage tank of liquid propellant should be appropriately reduced to improve its safety during the storage and use processes.The corresponding death radius in the accident was supposed to be 20-30 m,that was,the people stay within this range would be killed while the buildings and equipment would be completely destroyed.The safety zone free of the thermal radiant damage of samples was much greater than 30 m.The testing results of the deflagration process,the shock wave hazard and thermal radiation were well matched,indicating that the test data is true and reliable.The simulation results showed that the liquid propellant can be ignited successfully under the condition of fire,and the ignition position and ignition time were also confirmed.It makes up for the missing aviation kerosene fire temperature data in the external fire test,which further proves that the aviation kerosene used can meet the test demand and ensure sufficient time for the sample to react.The results provide a reference for the planning of explosive safety protection in the process of liquid propellant storage and transportation.