Combustion Characteristics Of Small Grain-Binding High-Burning-Rate Propellant

High-burning-rate propellant is widely used in quick response weapons such ashypervelocity kinetic antitank missiles, aircraft-launched missile, antitank missiles,etc. High-burning-rate propellant is one of the hottest research directions in the field ofsolid propellant. The investigated high-burning-rate propellant is characterized by highburning rate and stable combustion, the duplex structure of wchich is fabricated bybinding small grain propellants together by pasty propellant. In the paper, the formuladesign and combustion behavior of the novel high-burning-rate propellant is investigatedboth theoretically and experimentally.Firstly, the principle and method of designing the combustion characteristics ofsmall grain-binding high-burning-rate propellant are analyzed and discussed, theburning behaviors and energy characteristic of the component content and binder andsmall grain propellant are respectively calculated by the estimating burning rateprocedure based on the chemical structure and characteristic of propellant, and theREALthermodynamics system software. The selection principle of component contentwhen designing the burning behavior and energy characteristic is analyzed. According tothe formula design of the small grain-binding high-buming-rate propellant as well as thepreparation processes of both double base propellant and composite propellant, thenovel process to prepare small grain-binding high-burning-rate propellant characterizedby the room temperature, solventlessness and two-step extruding is proposed.Secondly, the effects of the component content, small grain shape and structure,and the binder mass ratio of binder to small grain propellant on the burning behavior ofthe small grain-binding high-burning-rate propellant were respectively studied.Theexperimental results show that, the burning rate of pasty binder and the propellantincreases with the increasing the component content of NC, NG and AP and that as theratio of NC/NG in the small grain increases, the burning rate of small grain increasesbut the burning rate of the propellant redueces. The internal laws can be concluded thatthe greater burning rate difference between pasty binder and small grain is, the higherthe burning rate of the propellant is, vice versa.The smaller the particle size and the rougher the surface leads to the higher theburning rate of the propellant. The smaller the mass ratio of the pasty binder to smallgrain is, the higher the burning rate of the propellant is. But when the mass ratio isreduced to a certain value, it would easy to cause unstable combustion. Based ontheoretical analysis, the mass ratio of the pasty binder to small grain should be t higherthan 41: 59. The catalytic properties of the thermal decomposition and the burning behavior ofthe small grain-binding high- burning-rate propellant is systemically investigated.Experimental results that, ee the addition of iron composite into the lead/copper complexcatalyst significantly advances the peak temperature of double base binder thermaldecomposition, showing excellent catalytic performace., and also promotes the thermaldecomposition of AP. Especially the complex of lead ferrocyanide/C.C reducestemperature of AP higher temperature decomposition peak by 133.4℃and temperatureof AP lower temperature decomposition peak by 55.1℃, and is a good complex catalystin the catalytic thermal decomposition of AP. Moreover, using lead/iron/coppercomplex catalyst greatly reduces the pressure exponent in the higher pressure range ofthe small grain-binding high-burning-rate propellant. Remarkably, the complex of leadferrocyanide/C.C shows excellent catalytic effect on the small grain-bindinghigh-burning-rate propellant.The analyzed of the photos of the small grain-binding high-burning-rate propellantduring combustion and after extinguishing, the combustion extinguished surface is not asimple curved surface, but a surface with multi-perforated permeable structure composeof the melt and conglutinated small grain propellant, where convective combustion maybe exist, and its combustion can be divided into six different zones, condensed phaseheating zone, hypo-surface reaction zone, combustion surface zone, permeabilitymultiperforated zone, grain flowing zone and product zone.Under different conditions, the combustion of the small grain-bindinghigh-burning-rate propellant can be categorized into three types, i.e. parallel layercombustion similar to double base propellant, convective combustion similar to thesuper high-burning-rate propellant, and finite convective combustion between the twotypes. The dimensionless value r and pressure can be used to estimate when the threecombustion type appears. When the pressure is low and r≈1.0, the combustion in therocket motor is similar to parallel layer combustion; when the pressure is higher and r＞1.4, the combustion in the rocket motor is similar to the convective combustion; andwhen the pressure is moderate and r≈1.1～1.3, the combustion in the rocket motor isfinite convective combustion.The coclusion can be drawn that the same propellant hasthree different combustion types under different conditions, which is the difference ofthe small grain-binding high-burning-rate propellant from traditional propellant and willprovide a wider application field for high-burning-rate propellant.