Studies On Thermal Decomposition,Burning Behavior And Its Application Of 5-aminotetrazole Based Propellant

With the gradual development of halon fire extinguishing agent substitution,the Solid Propellant Gas Generator(SPGG)fire extinguishing apparatus based on solid propellant rapid fire extinguishing(SPFE)technology stands out for its fast,efficient,compact structure and other excellent characteristics.It has attracted extensive attention of many researchers in the research and development of fire extinguishing equipment in aircrafts engine compartment,fuel dry compartment and armored vehicle personnel compartment.After years of research,the corresponding fire extinguishing device have been designed and manufactured using the 5-aminotetrazole/strontium nitrate(5-AT/Sr(NO3)2)based composite propellant and the vessel of halon fire extinguisher.However,the disadvantage of the used propellant,including high outlet temperature and unstable combustion behavior,have greatly hinder the wide spread use of SPGG fire extinguishing device.Therefore,5-AT/Sr(NO3)2 composite propellant is selected as the research object,and six typical different kinds of combustion regulator is adopted.The effects of each additive on the thermal decomposition behavior and combustion behavior of the propellant were deeply explored and analyzed,and the influence mechanism was also analyzed.Meanwhile,fire extinguishing experiments based on the built-up testing platform and self-made SPGG fire extinguishing principle prototype were carried out,the fire extinguishing efficiency of the apparatus with different formulations in closed chamber were characterized.Then the relation between the characteristics of propellant and the fire extinguishing efficiency of the apparatus was explored.The aim was to develop a new type of 5-AT based solid propellant that suitable for SPGG fire extinguishing device.The physical characteristic of each sample is characterized by means of SEM,specific surface area tester and thermal conductivity tester.The thermal decomposition behavior of samples at different heating rates under nitrogen atmosphere was tested by thermogravimetric-differential thermal analyzer and thermogravimetric-infrared spectrometer,and the calculated reaction kinetics parameters were used to exploring the potential reaction mechanism.The results show that the influence of each additive on the thermal decomposition process can be attributed to their effects on the three stages of the propellant’s decomposition reaction.In the first stage,the thermal conductivity of the sample and the distribution of the ingredient are the dominant factor.In the second stage,the coolant additives NQ and MA can accelerate the reaction in this stage by increasing the concentration of components in the gas phase reaction zone due to early thermal decomposition.Additives nano-CuO and nano-ZnO mainly act as catalysts for gas-phase reactions,in which nano-CuO mainly enters the gas-phase region and consumes HN3 while nano-ZnO accumulated on the combustion surface and catalyzes nitrogen-oxygen related reactions.The influence of coolant additives on the reactions at this stage depends on the balance between their own endothermic hindrance and the possible catalytic effect of their decomposition products.Al2O3 formatted from the decomposition of ZnAl2O4 and Al(OH)3 is the critical factor,which could accelerate the reaction in this stage.In the third stage,the thermal decomposition process of Sr(N03)2 is mainly affected by the additives themselves or their decomposition products.The theoretical combustion characteristic parameters,flame structure,combustion temperature,burning rate and combustion residue composition of samples with different additive were studied and analyzed by experimental test.Combining with the results of thermal decomposition behavior,a physical combustion model for each sample was proposed,and the influential mechanism of each additive on the combustion behavior was revealed.And the theoretical combustion model of 5-AT based propellant was established based on the GDF model.The variation of combustion behavior of solid propellant depends on the heat balance between gas phase reaction and condensed phase reaction at combustion surface.NQ,nano-CuO and Al(OH)3 could accelerate gas phase reaction,while MA,nano-ZnO and ZnAl204 have obvious influence on the condensed phase reaction,which is also reflected in the combustion flame structure.At the same time,the XRD analysis of sample solid residue also confirms the analysis of decomposition reaction route of 5-AT/Sr(NO3)2 composite propellant.The proposed physical combustion model exhibited a well explanation for the heat balance at the combustion surface after adding different additives.And the applicability of the theoretical combustion model also have been conducted.The theoretical fire extinguishing efficiency of SPGG extinguishing equipment with different propellant was calculated based on Saito method.The self-made principle prototype of SPGG extinguishing device and the fire extinguishing test platform were set up to carry out the fire extinguishing experiment in closed chamber to evaluate the fire extinguishing efficiency.The theoretical calculation result shows that when ultra-fine dry powder is selected as fire extinguishing medium,the theoretical fire extinguishing efficiency of SPGG extinguishing device is 2.77 times for the same weight Halon extinguishing agent.The experiment result shows that the burning rate,combustion temperature and ignition delay of the propellant are direct factor that could affect the extinguishing efficiency of the apparatus.With the propellant that have different characteristics combusted in the extinguisher chamber,the extinguishing medium could drive by gaseous combustion products with different temperature and pressure,then after spaying,it could have different cool effect and initial velocity,which could affect the extinguishing time.Therefore,in order to increase the extinguishing efficiency of the SPGG extinguishing equipment,a 5-AT based propellant with lower combustion temperature,higher burning rate and lower ignition delay is needed.Based on this analysis results,an optimized 5-AT based propellant doped with NQ,nano-CuO,and ZnAl2O4 is prepared and tested.Results showed that the combustion temperature of this propellant is only 885.91 K,the burning rate at 1 MPa is about 9%higher than 5-AT/Sr(NO3)2 propellant,and the pressure exponent of the burning rate is 0.22.And the extinguishing experiment results indicating that the extinguishing efficiency of the SPGG extinguishing equipment with this propellant is increased.It also confirmed that the proposed relation between the characteristics of propellant and the extinguishing effciency of SPGG extinguishing equipment.