Ammonium perchlorate-based composite solid propellant formulations with plateau burning rate trends

This paper presents burning rates as a function of pressure of several propellant formulations based on ammonium perchlorate (AP) and hydroxyl-terminated polybutadiene cured by isophorone diisocyanate, many of which exhibit significantly low (nearly zero or negative) values of the pressure exponent of the burning rate in distinct pressure ranges, termed as plateau burning rate trends. The propellants contain a bimodal distribution of AP particles with the size of the coarse and fine particles within narrow ranges whose mean values are widely separated. Two mean sizes of fine particles were considered for the propellant formulations in the present work, namely, 5 and 20 μm. These choices are based on the mid-pressure extinction behavior exhibited by the matrix of fine AP and binder contained in the propellants but when tested alone over a wide range of fine AP size and pressure. The propellants that include the fine AP/binder matrixes exhibiting a mid-pressure extinction, in turn, exhibit the plateau burning rate trends within the corresponding pressure ranges. A plateau is also observed at elevated pressures in the burning rates of some formulations, which is related to the diminishing relative importance of the near-surface leading-edge region of the oxidizer/fuel diffusion flame in the gas-phase combustion zone. The choice of the coarse AP size influences the exact pressure range within the mid-pressure extinction domain of the matrix where the propellant exhibits the plateau burning rate trends. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 4, pp. 73–81, July–August, 2007.     

Effect of pressure on the burning rate of composite propellants

Combustion, Explosion, and Shock Waves -     

黑索今对变燃速发射药力学及燃烧性能的影响

变燃速发射药在其内层中添加高能硝铵炸药黑索今达到了内层快速燃烧的目的,同时黑索今的引入也影响了整体发射药的力学性能.通过抗拉强度、剪切强度的测试对比及密闭爆发器燃烧现象的比较,得出结论,随着黑索今含量的增加,变燃速发射药抗拉强度和剪切强度均减小,同时燃烧渐增性变优;随着黑索今粒度的变大,发射药抗拉强度减小,同时燃烧渐增性变差.     

Effect of application of various ignition conditions in closed-vessel tests on burning rate calculation of a fine-grained propellant

The most widely used experimental method for determination of dynamic characteristics of gun propellant combustion is burning a specific amount of a propellant in a closed chamber (vessel) and measuring the resulting pressure versus time profile. The aim of this work is to conduct experimental investigations at different conditions of propellant ignition, which permit to verify the view on legitimacy of standard conditions of closed-vessel tests. This paper considers first of all the influence of conditions of propellant ignition during closed-vessel tests on possible deviations in determination of the burning rate. For this purpose, experimental tests of a fine-grained, single-base propellant are carried out in a conventional closed vessel and a micro-closed vessel, applying different ignition methods for the same loading density. The results of experimental tests and calculations show significant influence of the ignition system type used on determined values of the burning rate and other dynamic characteristics of propellant combustion, such as dynamic vivacity, absolute quickness, and relative quickness.     

提高碳氢富燃料推进剂燃速压强指数研究

研究了碳氢富燃料固体推进剂中固体组分的种类、含量、规格,燃速催化剂的种类、含量等因素对配方燃速压强指数(简称压强指数)的影响。结果表明,碳氢富燃料推进剂的压强指数随氧化剂含量的适度降低和固体碳氢燃料TQ粒度的减小而升高,当w(N9)为3%时,压强指数达到最高,以Mg作金属燃烧剂和以EM作燃烧催化剂的配方有较高的压强指数。通过优化上述因素,推进剂的压强指数达到了0.62~0.66。     

Burning rate anomaly of composite propellant grains

In this study, characteristics of the burning rate anomaly in composite propellant grains are investigated. The burning rate anomaly has been known as the “midweb anomaly” or the “hump effect.” This paper describes some results of an experimental study on effects of propellant formulations, casting processes, and viscosity of the propellant slurry on the phenomena. According to some past studies, it has been suggested that the geometry of the “isochrone surface” of the propellant slurry affects the local burning rate. To investigate the effect of the isochrone surface, visualization of the isochrone surface in composite propellant grains is carried out. A relation between the geometry and the local burning rate measured in motor firing tests and strand tests is proposed. As a result, besides the common static characteristics of the burning rate anomaly, i.e., the pressure hump effect and the nonisotropic characteristic of the local burning rate, a peculiar burning rate distribution in connection with the isochrone surface is obtained.     

Novel burning rate measurement technique for solid propellant by means of ultrasonics

A novel burning rate measurement technique for solid propellants using ultrasonics has been developed. Ultrasound is applied to the burning surface of the end-burning propellant grain from the bulk side, and the reflected wave, which is frequency-shifted by the Doppler effect, is analyzed with a wavelet technique. This method enables us to get the instantaneous linear burning rate and, thus, can be a strong tool for the instability study of solid propellants. The wavelet method is also favorable for the identification of the reflected signal from the burning surface even if the signal intensity becomes very low and indistinguishable from white noise with normal measuring techniques. Efforts have also been paid to eliminate the coupling material between the ultrasonic probe and the propellant grain to simulate the real situation of rocket motors. An oscillation deadener circuit has been successfully employed to reduce strong multi-deflection signals within a metallic plate between the probe and the propellant grain. With these two improvements, it becomes possible to detect and process the signals in longer propellant grains in the actual solid rocket motor situations.     

发射药洁净燃烧技术研究进展

概述了洁净燃烧发射药的研究情况,对非洁净燃烧发射药的影响进行了总结,重点分析了洁净燃烧的实现机理和途径,建议在未来的相关研究中对此加以重视.     

Erosive burning of a solid propellant in a supersonic flow

We present results of an experimental study of burning of a ballistite solid propellant (gun powder H) in a supersonic flow. It is shown that the criterial dependence of the erosion coefficient on the Vilyunov parameter obtained on the basis of experimental results in a subsonic and a supersonic flow describes satisfactorily experimental data for a supersonic flow in the examined range of Mach numbers M=1–2.8 as well. A more correct approximation formula for the range of parameters considered is derived. The specific features of the flow along the surface of a solid propellant at M>1 is analyzed, and this analysis has revealed some problems in the interpretation of experimental data. Translated fromFizika goreniya i Vzryva, Vol. 34, No. 1, pp. 61–64, January–February, 1998.     

Effect of orientation on burning rate of solid combustible

The effect of orientation on the combustion phenomena of a PMMA plate was studied experimentally. A PMMA plate was held by a sample holder made of insulation boards with only one face exposed to the air. Observation of burning inclined plates revealed that flame shape varied with inclination angle. The burning behavior of the upper surface of an inclined plate appeared to differ from that of the lower surface. However, the surface regression rate was found to depend on the inclination angle from the vertical plane. This rate for the upper surface was identical to that of the lower one if the absolute value of the inclination angle was identical, and was found to depend on empirical relationships involving natural convective heat transfer around a heated plate.     

Characterization of a glycidyl azide polymer composite propellant: Strain rate effects and relaxation response

Uniaxial tension tests were completed on a developmental GAP/PSAN solid rocket propellant at constant strain rates ranging over three decades and at five different temperatures. An analysis of the maximum stress (strength) and the strain at maximum stress showed that there is a relatively narrow range of temperatures and strain rates that give rise to strains at maximum stress that exceed 18%. The long-term equilibrium strain capability (strain endurance) appears to be between 10% and 12%. The trend of the strength and initial deformation moduli were log-linear with the reciprocal of the strain rate across three decades. However, the shifted master curves were log-curvilinear in form. The relationship between the strength and the initial modulus can be approximated by a power law. A series of stress relaxation tests was completed at a level of 4% strain and at five different temperatures. The initial portion of the shifted master relaxation curve is concave-up with correspondingly high stresses and moduli. It decays with time approaching a log-constant slope. Tensile moduli derived from constant strain rate tests were found to be consistently higher in value than the moduli as a function of time determined from relaxation tests, for an equivalent shifted time. Preliminary evidence suggests that the tensile modulus as a function of the reciprocal of shifted strain rate can be equated to the relaxation modulus as a function of shifted time through an adjustment factor. This relationship extends the relaxation modulus results back a further three and one-half decades of shifted time. © 1995 John Wiley & Sons, Inc.