Showing papers on "Burn rate (chemistry) published in 2006"

Revisiting the Modeling of Ammonium-Perchlorate Combustion: Development of an Unsteady Model

Abstract: This paper examines afresh features of ammonium-perchlorate (AP) combustion. Here an AP model, which predicts most experimental observations, is proposed. The one-dimensional aero-thermo-chemical field is captured through the solution of mass, energy, and species conservation equations. The unsteady one-dimensional phase heat transfer accounting for regression is solved for in the condensed phase. The uncertain parameters for AP pyrolysis, gas-phase reaction, and extent of surface exothermicity are chosen so that the most certain of the measured parameters of AP combustion, namely, pressure index of stable combustion (0.77 between 2 and 7 MPa), initial temperature sensitivity of burn rate, σp (about 0.0021 to 0.0015 K −1 ), range of surface temperatures measured and suggested in several studies (∼850 to 875 K), and low-pressure deflagration limit (LPDL) at 300 K (∼2 MPa), are correctly predicted. The results obtained show the pressure index of AP combustion to be 0.77 and σp to be 0.0024‐0.0023 K−1. The LPDL is caused by a combination of loss of liquid layer and transient conduction into the condensed phase and not by heat loss.

Dead Zones in LX-17 and PBX 9502

Abstract: Pin and X-ray corner turning data have been taken on ambient LX-17 and PBX 9052, and the results are listed in tables as an aid to future modeling. The results have been modeled at 4 zones/mm with a reactive flow approach that varies the burn rate as a function of pressure. A single rate format is used to simulate failure and detonation in different pressure regimes. A pressure cut-off must also be reached to initiate the burn. Corner turning and failure are modeled using an intermediate pressure rate region, and detonation occurs at high pressure. The TATB booster is also modeled using reactive flow, and X-ray tomography is used to partition the ram-pressed hemisphere into five different density regions. The model reasonably fits the bare corner turning experiment but predicts a smaller dead zone with steel confinement, in contradiction with experiment. The same model also calculates the confined and unconfined cylinder detonation velocities and predicts the failure of the unconfined cylinder at 3.75 mm radius. The PBX 9502 shows a smaller dead zone than LX-17. An old experiment that showed a large apparent dead zone in Composition B was repeated with X-ray transmission and no dead zone was seen. This confirms the idea that a variable burn rate is the key to modeling. The model also produces initiation delays, which are shorter than those found in time-to-detonation.

New Additives for Modifying the Burn Rate of Composite Solid Propellants

Abstract: The ability of nano-particle additives to tailor the burning rate of composite solid rocket propellants is being explored in the authors’ laboratories. In the present study, two different nano-particles and two separate styles of mixing in the additive were investigated. These variations were tested on a typical HTPB/AP composite rocket propellant with varying characteristics. After a baseline study was completed without additives, a Taguchi L8 matrix was designed to fully test the effect of six different mixture variables and the two different additives on the burning rate. The propellants were tested in a strand bomb at pressures ranging from approximately 34 to 136 atm, and some representative data are provided. The results thus far indicate that small levels of nano-particle additives (∼ 1 wt %) can have significant effects on the magnitude and pressure dependence of the composite propellant.

Burn-rate Measurement on Small-scale Rocket Motors

Abstract: Small-scale rocket motors are widely used by propulsion industries to carry out burn rate measurement for a variety of needs. Several automated data-reduction procedures have been implemented to derive burn rate from pressure-time profiles resulting from experimentation. Even if these are easy and fast to use, these procedures are not completely reliable in that these measure only the average behaviour of a motor. A new model has recently been proposed to overcome this problem. However, it was soon noticed that the results depend on the propellant grain production and forming processes even if the motor hardware is the same. A series of propellant grains has been produced to be sampled to map the local ballistic behaviour and changes introduced by the manufacturing process. In this study, sampling and testing procedures are reported and the results of an almost complete grain mapping are discussed.

Kinetic Modeling of Slow Energy Release in Non-Ideal Carbon Rich Explosives

Abstract: We present here the first self-consistent kinetic based model for long time-scale energy release in detonation waves in the non-ideal explosive LX-17. Non-ideal, insensitive carbon rich explosives, such as those based on TATB, are believed to have significant late-time slow release in energy. One proposed source of this energy is diffusion-limited growth of carbon clusters. In this paper we consider the late-time energy release problem in detonation waves using the thermochemical code CHEETAH linked to a multidimensional ALE hydrodynamics model. The linked CHEETAH-ALE model dimensional treats slowly reacting chemical species using kinetic rate laws, with chemical equilibrium assumed for species coupled via fast time-scale reactions. In the model presented here we include separate rate equations for the transformation of the un-reacted explosive to product gases and for the growth of a small particulate form of condensed graphite to a large particulate form. The small particulate graphite is assumed to be in chemical equilibrium with the gaseous species allowing for coupling between the instantaneous thermodynamic state and the production of graphite clusters. For the explosive burn rate a pressure dependent rate law was used. Low pressure freezing of the gas species mass fractions was also included to account for regions where the kinetic coupling rates become longer than the hydrodynamic time-scales. The model rate parameters were calibrated using cylinder and rate-stick experimental data. Excellent long time agreement and size effect results were achieved.

Large-Scale Hybrid Motor Testing

Abstract: Hybrid rocket motors can be successfully demonstrated at a small scale virtually anywhere. There have been many suitcase sized portable test stands assembled for demonstration of hybrids. They show the safety of hybrid rockets to the audiences. These small show motors and small laboratory scale motors can give comparative burn rate data for development of different fuel/oxidizer combinations, however questions that are always asked when hybrids are mentioned for large scale applications are - how do they scale and has it been shown in a large motor? To answer those questions, large scale motor testing is required to verify the hybrid motor at its true size. The necessity to conduct large-scale hybrid rocket motor tests to validate the burn rate from the small motors to application size has been documented in several place^'^^.^. Comparison of small scale hybrid data to that of larger scale data indicates that the fuel burn rate goes down with increasing port size, even with the same oxidizer flux. This trend holds for conventional hybrid motors with forward oxidizer injection and HTPB based fuels. While the reason this is occurring would make a great paper or study or thesis, it is not thoroughly understood at this time. Potential causes include the fact that since hybrid combustion is boundary layer driven, the larger port sizes reduce the interaction (radiation, mixing and heat transfer) from the core region of the port. This chapter focuses on some of the large, prototype sized testing of hybrid motors. The largest motors tested have been AMROC s 250K-lbf thrust motor at Edwards Air Force Base and the Hybrid Propulsion Demonstration Program s 250K-lbf thrust motor at Stennis Space Center. Numerous smaller tests were performed to support the burn rate, stability and scaling concepts that went into the development of those large motors.

Determining the unsteady combustion behavior of propellants from results of closed-bomb testing

Abstract: Two methods for processing the results of closed-bomb tests of propellants are proposed: a method for determining the force of propellant, the covolume of propellant gas, and the pressure dependence of the degree of propellant combustion that takes into account the heat exchange between the combustion products and the walls of the closed bomb; a procedure for determining the linear behavior of unsteady combustion in the form justified by Ya. B. Zel’dovich. It is shown that accounting for heat losses is necessary not only to determine the force of propellant and the covolume of propellant gas but also to determine the combustion behavior.

Application of Energy‐Saturated Complex Perchlorates

Abstract: We have synthesized several of new energetic complex perchlorates According to the data of derivatographic analysis, the complexes are thermally stable compounds. One of the promising ways of regulating ballistic characteristics of highly filled energetic formulations is the introduction of modifiers of burning. Complex compounds of d‐metals are effective modifiers of the process of burning. Ballistic tests were made in a constant pressure bomb and demonstrated that the prepared compounds are promising modifiers of the burn rate and can be used in the developed formulations of rocket propellants.

Effects of thermo-physical and flow parameters on the static and dynamic burning of a cigarette

Abstract: Effects of thermo-physical and operating parameters influencing the combustion of a cigarette were systematically studied using a three-dimensional first-principles-based mathematical model. Thermo-physical properties include packing density and thermal conductivity of materials forming the packed bed in the cigarette, and operating parameters include ambient oxygen concentration, air flow rate through the cigarette, and the ambient cross flow. The model was first validated with the existing experimental data which provided a satisfactory result. Increasing the ambient cross flow while increasing the burn rate and temperatures in the cigarette column, decreases the delivery of gaseous products owing to air infiltration through the paper into the column and enhances diffusion of gases out of column. Reducing the oxygen concentration reduces the burn rate to a point at which burning would be extinguished during the smoldering step. Increasing the air flow monotonically increases the burn rate, temperature a...

Simulation of the internal ballistics of a liquid propellant engine start system in comparison with experimental verification

Abstract: There are several methods for starting a complex mechanical system, for example a liquid propellant engine. One of common methods is the use of solid propellant gas generator that is named solid propellant starter. In this method, a solid propellant motor is used for gas generating and leading it towards power generation turbine. The turbine as an active element, rotates one or several pumps for providing propellants with suitable head and rate for consumers such as liquid propellant gas generator and combustion chamber. After moving of pumps and reaching to nominal conditions, the start system stops. Therefore in order to suitable and optimized designing of starter, the essential parameter is taking into account the downstream resistance of system. In a complex system such as a liquid propellant engine, the start system is one of the main and important components of engine and it's operation affects directly on the other components of engine. Therefore the optimized designing of it, has special importance. On the one hand, the selection of solid propellant geometry (grain) that exist in this system, is one of main parameters and the most important function in the process of start system designing, because the geometry of solid propellant is determinant of burning area and consequently the burning pattern of solid propellant. Therefore it is an important factor in determining the performance of starting system. In this paper, the alterations of pressure and thrust of a starter with different solid propellant grains have been simulated and have been compared with experimental results. The very good agreement of theoretical and experimental results indicates that the accuracy of simulation process is excellent.

Study on Burning Rate Inhibitors of HTPB/AP/Al Propellants

Abstract: The effect of ammonium oxalate,lithium fluoride,calcium carbonate,strontium carbonate,quaternary ammnium salt and etc.as burning rate inhibitors on burning rate of HTPB/AP/Al propellant have been investigated.Considerable decrease in burning rate has been observed when quaternary ammonium salt composite with carbonate or lithium fluoride are used as depressant,and above-mentioned composite inhibitors have excellent effect on decreasing the burning rate of propellants.In HTPB/AP/Al propellants,the quaternary ammonium salts composite with carbonates are more pronounced on decreasing burn rate than ammonium oxalate inhibitor which is now used for many practical low burning rate propellant.The firing tests of BSFФ75mm motors indicate that quaternary ammonium salt composite with carbonate also could decrease the pressure exponent of the propellant from 0.33 to 0.20 in the pressure range of 3.45～12.17MPa.The firing test of BSFФ165mm motors loaded with HTPB/AP/Al propellant grain containing quaternary ammonium salt and carbonate as inhibitor gives more stable chamber pressure-time and thrust-time histories than that containing ammonium oxalate,and the results show that the density-specific impulse of obtained formulation is 2.8% higher than that containing ammonium oxalate with the same burning rate.

Burn-Rate Modeling and Combustion Diagnostics for Environmentally Friendly, Solid Rocket Propellants

Abstract: : Advanced, burn-rate, propellant modeling is critical for developing new rocket missile and gun propellants for Future Combat Systems and for providing a fundamental screening tool that can result in substantial cost savings compared to missile and gun firings. In this paper, we report the detailed chemical kinetics and burn rate prediction of tri-aminoguanidinium azotetrazolate (TAGzT) and nitrocellulose (NC).

Mesoporous iron oxide energetic composites with slow burn rate, sustained pressure and reduced ESD sensitivity for propellant applications

Abstract: .................................................................................vi LIST OF FIGURES.......................................................................ix LIST OF TABLES........................................................................xi CHAPTER

Promoted Combustion Testing of Pure and Ceramic-Coated Metals in High Pressure Oxygen by the Federal Institute of Materials Research and Testing (BAM)

Abstract: The new promoted ignition combustion test apparatus at BAM matches the requirements of ASTM test method G 124 [ASTM G 124, Standard Test Method for Determining the Combustion Behavior of Metallic Materials in Oxygen-Enriched Atmospheres, 2003] and of EIGA publication, IGC Doc 13/02/E [EIGA Gas Association Document IGC Doc 13/02/E, Oxygen Pipeline Systems, 2003]. The test apparatus is most likely the only one in Europe. The test chamber allows investigations with pure oxygen or oxygen mixtures at pressures up to 500 bar and at temperatures up to 400°C at static or flowing gas conditions. The ignition device consists of an electrical ignition wire and a promoter. IR-sensors, distributed over the whole length of the rod, measure and record the burning temperature and allow measurement of the burn rate. A video system records the experiment for visual characterization of the burning behavior. BAM test results are compared with published data. Results on investigations with coated rods are presented. Ceramic coatings seem to be a solution for the use of certain less compatible metallic materials at higher oxygen pressures.

Combustion performance of DNTF-CMDB propellant

Abstract: The factors affecting burning rate and pressure exponent of DNTF-CMDB propellant were studied,including the content of DNTF,the different catalyst systems,the contains of carbon black and the granularity of DNTFThe results show that when the content of DNTF is 30%,the pressure exponent of propellant can be decreased to 037 by the composite catalyst system of energetic lead salt,aromatic cuprum salt and carbon black in 8～14MPaWhen the content of DNTF is 50%,the pressure exponent of propellant can not be suppressed by the composite catalyst system of common Pb-Cu-CB(including energetic lead salt and aromatic lead salt and aromatic cuprum salt)The burningrate and pressure exponent of propellant will increase with the increasing content of carbon blackThe burningrate of propellant can be affected by the granularity of DNTF obviouslyThe larger granularity of DNTF is,the higher burningrate is(5319mm/s,16MPa),and pressure exponent increases

Improvement of Burning Rate for Solid Propellants by ACP

Abstract: Extraordinary and outstanding effect of improving the burning rate of modified double-base propellant,AP based composite propellant and N-15D propellant was achieved with fast-burning energetic material ACP.The burning rates of propellants were all substantially improved but the pressure exponent was not changed basically by incorporating ACP with different particle size and content into HMX-and RDX-based modified double-base propellants.The burning rate was greatly increased by incorporating ACP into AP based composite propellant and the pressure exponent was superior to 0.45 at 7～15MPa.It was successfully tested on the Φ64mm motor and p-t curve was obtained.The burning rate of base formulation was quite low when incorporating ACP into N-15D propellant,but the burning rate was still improved and the pressure exponent was increased slightly.The increments of the burning rate were 40.62% for HMX-based modified double propellant,38.00% for RDX-based modified double propellant,37.35% for AP based composite propellant and 9.90% for N-15D propellant.

Gas Generation Rule about Tubular Gun Propellant with Two Different Burning Rate Layers

Abstract: To establish the Γ vs.Ψ expression,the gas generation rule about tubular gun propellant with two different burning rate layers was theoretically analyzed.Under the precondition of following the geometric combustion law,the equations describing Γ vs.Ψ relation of this kind of variable burning rate gun propellant were derived by using its initial geometric size,burning-rate ratio and density ratio of internal and external layer as the basic variables.The critical length-to-diameter ratio needed for elaborating the characteristics of progressive combustion of this gun propellant was obtained.The influences of inner diameter,length-to-diameter ratio and burning-rate ratio of this gun propellant on its gas generation rule were discussed through calculated Γ-Ψ curve examples.The calculated results showed that this tubular gun propellants with two layers can present progressive combustion in early stage while a step of Γ in intermediate or late stage when the initial geometric size and burning-rate ratio have proper values.

LX-17 Deflagration at High Pressures and Temperatures

Abstract: We measure the laminar deflagration rate of LX-17 (92.5 wt% TATB, 7.5 wt% Kel-F 800) at high pressure and temperature in a strand burner, thereby obtaining reaction rate data for prediction of thermal explosion violence. Simultaneous measurements of flame front time-of-arrival and temporal pressure history allow for the direct calculation of deflagration rate as a function of pressure. Additionally, deflagrating surface areas are calculated in order to provide quantitative insight into the dynamic surface structure during deflagration and its relationship to explosion violence. Deflagration rate data show that LX-17 burns in a smooth fashion at ambient temperature and is represented by the burn rate equation B = 0.2P{sup 0.9}. At 225 C, deflagration is more rapid and erratic. Dynamic deflagrating surface area calculations show that ambient temperature LX-17 deflagrating surface areas remain near unity over the pressure range studied.

The Influence of Specific Heats Variability on Heat Release Analysis Using Two-Zone Models

Abstract: Heat release and burn rate analysis in Internal Combustion Engines (ICEs) are usually based on a zero-dimensional application of First-Law of thermodynamics. In order to evaluate the heat release models available in literature use the differential form of the energy conservation equation, generally neglecting specific heats derivative terms. In this work the effects of specific heats derivative terms on a two-zone heat release model, for a Spark Ignition (SI) engine, have been evaluated. Results obtained with and without considering specific heats derivative terms have been compared. These comparisons show that proposed modifications allow to obtain more regular curves especially for mass fraction burned and heat release according to the combustion phenomenology. Besides, taking into account the specific heats derivative terms, the model's calibration constants do not need to be tuned, and the combustion efficiency can be evaluated directly by the mathematical model (otherwise experimentally measured).Copyright © 2006 by ASME