Showing papers on "Burn rate (chemistry) published in 1993"

Solid propellant combustion mechanisms and flame structure

Abstract: AP and HMX are the two oxidizers used most often in modern solid propellants, either composite propellants or composite modified double base propellants. Although the two oxidizers have very similar combustion characteristics as monopropellants, they lead to significantly different characteristics when combined with binders to form propellants. Also, different characteristics result depending on the particular binder system used. This paper discusses various flame structures and mechanisms that apparently lead to these similarities and differences, with emphasis on the qualitative effects of flame structure on combustion mechanisms. For AP composite propellants, the primary flame is more energetic than the monopropellant flame, leading to an increase in burn rate over the monopropellant rate. This also leads to a very strong particle size dependence. In contrast the HMX primary flame is less energetic than the HMX monopropellant flame and ultimately leads to a propellant rate significantly less than the monopropellant rate in composite propellants. In HMX composite propellants the primary flame apparently robs energy from the monopropellant flame leading to a reduced rate with little particle size dependence. In double base propellants HMX has little effect on the burning rate.

High velocity impulse rocket

Abstract: An improved high energy impulse rocket includes a motor case containing propellant composed of individual, free flowing granules of a predetermined shape and unbonded to said motor case. The propellant has a high burning rate of 100 milliseconds or less and generates chamber pressures of up to about 50,000 psi. The rocket motor includes a reentry nozzle open at one end and connected to an exit nozzle, the reentry nozzle forming an annulus to contain the propellant and also forming a barrier to prevent ejection of the propellant during burning. Acceleration of the rocket assists in maintaining the propellant within the motor case, which acceleration may be as high as 20,000 g generating a velocity as high as 10,000 fps. Such a rocket offers unique advantages, especially as a device to punch an opening in a wall structure, the details of which are described as well as other details of the improved and relatively inexpensive impulse rocket.

Solid Propellant Combustion and Internal Ballistics of Motors

Abstract: Publisher Summary This chapter discusses the solid propellant combustion and internal ballistics of motors. The combustion of a solid propellant is characterized by the way its surface regresses once it begins to burn. The burning rate is the distance traveled by the flame front per unit of time, measured normally to the burning surface. The burning rate is obtained by the strand useful length and the duration of the firing. The latter is determined by monitoring the noise created by the combustion. The advantage of this method is that a preliminary lateral restriction of the strand is not necessary. The introduction during the manufacturing of ballistic catalysts in propellant compositions allows the regulation of the burning-rate level and a significant decrease in the values of temperature coefficients and pressure exponents. Heterogeneous propellants contain a mixture of these ingredients, while decomposition releases gaseous products whose nature is either oxidizing or reducing. The addition of low-particle content, as ingredients in the propellant, is often successful in stabilizing motor combustion. This is particularly true in the case of tangential instabilities.

Ballistics of solid rocket motors with spatial burning rate variations

Abstract: Introduction T HE solid rocket motor (SRM) ballistician has the job of predicting the chamber pressure and thrust history for both new and existing motors utilizing propellant burning rate and grain geometry, ambient conditions, and nozzle geometry. For motors which do have a test history, ballisticians introduce a constant "scale factor" to force predictions to match actual burn times of test units as well as a time varying multiplier to improve "pointwise" matching of the pressure history. This pointwise burning anomaly rate factor, or BARF, is usually established as a function of web distance since it is generally acknowledged that the factor accounts for spatial burning rate variations within the grain. This ubiquitous quantity has gone by several names through the years: hump factor, surface burn rate error (SBRE), and residual error to name a few. Since the scale factor forces the average burning rate to match that in the test, the net integration of the BARF curve should have no effect on burning time. For most motors, the result takes on a hump-shaped appearance with maximum errors in burning rate usually being between 2-10%. Burning rate errors of this magnitude translate to errors in pressure of 3-15% due to the nonlinear dependence of pressure on this parameter. Errors introduced due to the present technique for predicting ballistic response can require grain redesign and additional static tests. In addition, initial uncertainties in the ballistic prediction of maximum chamber pressure impacts the design of motorcase, nozzle, and insulation components since these parts must be designed for "worst case" predictions. Even if initial tests are deemed to be adequate, thrust history variations from the optimal design can cause losses in payload capability. Finally, spatial burning rate variations not normally considered by the ballistician can lead to changes in insulation exposure times when compared with current prediction methodologies. This Note will investigate means to improve ballistic predictions by determining the contribution of spatially dependent burning rate variations to the BARF effect for a simple cylindrical-port motor. Background associated with research into BARF effects is provided in the next section, followed by a description of the technical approach. An analysis of a simple ballistic test motor follows this discussion, along with conclusions from the study. While propellant strain, grain deformations during pressurization, local gas velocity effects, and possible migration of propellant constituents have all been theorized to contribute to BARF effects, the primary influence appears to be attributable to spatial variations in the local burning rate within the propellant grain. We make this assumption because the "hump shaped" character of the curve seems to be consistent across many motors of varying grain geometry, case deformations, and propellant formulations. In nearly all cases, spatial burning rate variations are attributed to one of two effects resulting from the rheological processes undertaken in loading

Castable double base propellant containing ultra fine carbon fiber as a ballistic modifier

Abstract: Propellant formulations are provided which include non-toxic burn rate modifiers. In order to produce a usable propellant formulation, it is necessary to control the burn rate of the propellant. Failure to adequately control the propellant burn rate often results in unacceptable performance of the propellant. It has been found that carbon fibers are capable of modifying the burn rate of propellants without resorting to lead as a burn rate additive. Accordingly, the use of from about 0.5% to about 6.0% carbon fibers is taught as effective burn rate modifiers in propellants, in order provide non-toxic means for modifying the propellant burn rate.

Spectral Studies of Solid Propellant Combustion IV: Absorption and Burn Rate Results for M43, XM39, and M10 Propellants

Abstract: : An optical absorption experiment coupled to a windowed strand burner has been used to obtain dark zone temperatures and nitric oxide concentrations for two nitramine propellants (M43 and XM39) and a single base propellant (M10). Moreover, burn rates as a function of pressure were determined from the video record of the propellant burns. These measurements were taken over a pressure range from 0.8 to 2 MPa.... Burning rate, Optical absorption, Propellant combustion, Solid propellants

Development of a dual-frequency microwave burn-rate measurement system for solid rocket propellant

Abstract: A DUAL-FREQUENCY microwave burn-rate measurement system for solid rocket motors has been developed. The system operates in the X-band (8.2-12.4 GHz) and uses two independent frequencies operating simultaneously to measure the instantaneous burn rate in a solid rocket motor. Computer simulation and limited laboratory testing of the system were performed to determine its ability to limit errors caused by secondary reflections and by uncertainties in material properties, particularly the microwave wavelength in the propellant. Simulations showed that the frequency ratio and the initial motor geometry determined the effectiveness of the system in reducing secondary reflections. Overall, the simulations showed that a dual frequency system can provide up to a 75% reduction in burn-rate error over that returned by a single-frequency system. The hardware and software for dual-frequency measurements was developed and tested; however, further instrumentation work is required to increase the data acquisition rate so its full potential can be realized.

Propulsion Elements for Solid Rocket Motors

Abstract: Publisher Summary This chapter presents an overview of the propulsion elements for solid rocket motors. A rocket motor is designed to ensure that combustion occurs under pressure of the propellant grain it contains. The resulting gases are expanded through a nozzle, whose function is to convert this pressure into supersonic exhaust. A rocket motor has five major components. The first component is a case, which is made either of metal or composite materials by filament winding. Another component is a propellant grain, which can be of two types, namely, free-standing grains and case-bonded grains. Thermal insulation and nozzles are the next two components, while the fifth is an ignition system, which brings the energy necessary to the surface of the propellant to start burning. Ignition systems for small propellant grains are limited to a primer linked to a primary powder charge or a primer and an increment. The rocket motor operation point corresponds to the equality of the gas flow rates created from the combustion of the propellant grain ejected by the nozzle. For preliminary calculations, it is assumed that propellants burn in parallel layers and that the burning rate is only a function of the pressure. Usually the burning rate of a propellant, in terms of an intrinsic property of the material used, is obtained by using small motors that have a constant propellant burning area and a constant operation pressure.

Ageing Studies on a Composite Propellant Containing a New Organo-Copper Burn Rate Catalyst

Abstract: : The effect of a new organo-copper burn rate catalyst on the aging properties of an HTPB/AP based composite propellant has been studied and compared with a similar propellant containing copper chromite. The degradation of the propellant surface under conditions of thermo-oxidation was studied by monitoring oxygen uptake using a gravimetric technique. The oxidative induction times for the reaction were determined for a series of elevated temperatures and the data used to predict the storage life of the propellant at ambient temperatures using an Arrhenius plot. It was shown that the storage life of a copper chromite propellant was approximately 7.5 years at 20 deg C while the corresponding organo-copper propellant had a storage life of approximately 49 years. Surface aging processes, Thermal oxidative degradation, Copper catalysts Burn rates, Copper chromite.