Showing papers on "Burn rate (chemistry) published in 2001"

Coupled fluid-structure 3-d solid rocket motor simulations

Abstract: We describe our numerical method for three- dimensional simulations of solid rocket motors in which the internal gas dynamics, the combustion of the propellant, and the structural response are fully coupled. The combustion zone is treated as a thin layer using appropriate jump conditions, and the re- gression rate is determined using a nonlinear dynamic combustion model. An Arbitrary Lagrangian- Eulerian formulation is used in the gas dynamics and structural mechanics modules to follow the regres- sion of the propellant. We demonstrate the parallel scalability of our ALE implementation and its ability to handle significant burn back of the propellant on a model problem with a very high burn rate.

High energy propellant with reduced pollution

Abstract: This invention relates to energetic compositions, which offer increased performance in conjunction with a total absence of hydrogen chloride in the combustion products. The formulation avoid the use of halogen based oxidizers to prevent the formation of halogen based byproducts. The formulations disclosed herein use ammonium dinitramide as a primary oxidizer, which is a more energetic molecule than ammonium perchlorate. The solid propellant formulations disclosed herein comprise about 5.0 to about 10.0 weight % of at least one energetic binder; about 20.0 to about 35.0 weight % of an energetic plasticizer; about 25.0 to about 45.0 weight % of ammonium dinitramide as a primary oxidizer; about 0.0 to about 20.0 weight % of particulate aluminum having a particle size of about 1 μm to about 60 μm; and about 0.0 to about 20.0 weight % of ultrafine aluminum having a particle size of less than 1 μm. In addition to the ingredients in this basic formulation will be cure catalysts, curatives, crosslinkers, burn rate catalysts and modifiers, thermal and aging stabilizers other such ingredients commonly utilized in solid propellant formulations.

Combustion system for a heater

Abstract: A combustion system for a portable forced air heater having two frusta-conical sections attached to a circular burner tube, wherein each frusta-conical section has pre-determined vent hole patterns that allow the gas heater to have a variable burn rate.

端面燃焼式ハイブリッドロケットの基礎研究:その2 燃焼特性

Abstract: To overcome defects of conventional hybrid rockets such as the loss of specific impulse, which is caused by the O/F shift during the combustion, and the low combustion efficiency, the authors have proposed a new idea of design. The point of this idea, named “End-Burning Hybrid Rocket, ” is that oxidizer gas flows in the gap space of a porous solid fuel bed. Diffusion flame is formed at the end of the solid fuel bed. Experimental studies were made to clarify the basic combustion characteristics of the propellant. Results show that pressure exponent of the burning rate with the same equivalence ratio is approximately 0.85 and virtually independent with the equivalence ratio. Using this result, a designing method of End-Burning Hybrid Rocket Motor is shown. Finally, thrust and specific impulse is estimated as functions of oxidizer gas flow rates to investigate the throttling characteristics of the motor.

Dynamic Vivacity and Its Application to Conventional and Electrothermal-Chemical (ETC) Closed Chamber Results

Abstract: : Historically, dynamic vivacity has been used extensively in propellant lot acceptance. More recently, dynamic vivacity has been used in the analysis of closed chamber experimental data to assess propellant grain surface area behavior during combustion. The objective of this report is to: (a) examine the physical meaning of dynamic vivacity; (b) theoretically explore the behavior of dynamic vivacity for conventionally ignited charges of various geometries, including layered propellant charges; and (c) determine the appropriate method for applying dynamic vivacity to electrothermal-chemical (ETC) closed chamber data. The results presented indicate that dynamic vivacity is a robust statistic for assessing grain surface area behavior during combustion as long as the burn rate exponent in Vielle's Law is between approximately 0.7 and 1.0. if the burn rate exponent is greater than 1.0, the nature of the propellant surface area deduced from the dynamic vivacity appears to be distorted. In these cases, the dynamic vivacity always indicates a progressive grain geometry. From the cases studied, it appears that grain fracture during combustion will not significantly change the dynamic vivacity results unless the original grain possess a progressive grain geometry and the fractured grain pieces are relatively large. Finally, it appears that ETC ignition does not impact the shape of the dynamic vivacity curve but only affects the magnitude of the curve.

Intermittent burning and its contribution to plateau burning of composite propellants

Abstract: The plateau burning behavior of composite solid propellants consisting of ammonium perchlorate (AP) and hydrocarbon (HC) binder with a bimodal AP particle size distribution (coarse and fine) is examined. The focus is the weak pressure dependence of the propellant burn rate (i.e., a plateau) in an intermediate range of about 2.7-6.9 MPa (-400-1000 psi). The relationship between the appearance of this mid-pressure plateau for a composite propellant and self-extinction during the burning of the corresponding fine AP/binder matrix (i.e., the propellant formulation without the coarse AP particles) is experimentally examined through the study of a compositional array of propellants, sandwiches (two-dimensional propellants) and matrixes. The burning history of the samples was captured with a highspeed digital camera, and surfaces from quenched samples (burning that was self-extinguished or intentionally interrupted) are analyzed using a scanning electron microscope. The combined results indicate the prevalence of intermittent burning of the matrixes as the pressure is varied across the boundary between continuous burning and self-extinction (burn/no-burn boundary). The burning surfaces are marked by extreme threedimensionality coupled with a redistribution of the fine AP particles and the binder. The results point to the need for a more realistic approach to the underlying processes that contribute to plateau burning rate trends in bimodal composite propellants than has been adopted hitherto.

Comparison of in-cylinder coherent anti-Stokes-Raman scattering temperature measurements with predictions from an engine simulation

Abstract: The objective of this work was to compare the burned gas temperature measured using coherent anti-Stokes-Raman scattering (CARS) with the predictions of a multiple-zone computer simulation of combustion. The tests were at various engine operating conditions with different fuels. Mean cycle modelling was used initially to obtain the appropriate heat transfer tuning parameters for the engine simulation by matching to the cylinder pressure. The predicted mean cycle burned gas temperatures gave good agreement with the measured mean temperatures. Similarly, cycle-by-cycle modelling produced burned gas temperatures that agree with the measured values.This work showed that the multi-zone computer simulation could accurately predict the burned gas temperature once the fuel burn rate and completeness of combustion have been analysed and the model tuned correctly. The effects of methanol, methane, toluene and iso-octane on the burned gas temperature were investigated. It was found that the fuel burn rate an...

Damage of a high-energy solid propellant and its effects on combustion

Abstract: In order to improve the safety of high-energy solid propellants, a study is carried out for the effects of damage on the combustion of the NEPE (Nitrate Ester Plasticized Polyether) propellant. The study includes: (1) to introduce damage into the propellants by means of a large-scale drop-weight apparatus; (2) to observe microstructural variations of the propellant with a scanning electron microscope (SEM) and then to characterize the damage with density measurements; (3) to investigate thermal decomposition; (4) to carry out closed-bomb tests. The NEPE propellant can be considered as a viscoelastic material. The matrices of damaged samples are severely degraded, but the particles are not. The results of the thermal decomposition and closed-bomb tests show that the microstructural damage in the propellant affects its decomposition and burn rate.

Theoretical Analysis of the Effects of Cigarette Design Parameters on the Smoldering Rates, Heat Flux, and Total Heat Released during Smoldering of a Cigarette

Abstract: A mathematical model developed by Muramatsu, Umemura, and Okada (1979) was modified and improved by changing the relative amounts of radiative and conductive heat transfer to study the effects of moisture content in the cigarette, cigarette packing density, and cigarette circumference on the smoldering rates, heat flux, and total heat released during natural smolder of a cigarette.A mathematically predicted temperature profile was fitted to the corresponding experimental values with a nonlinear least-square fitting routine to obtain a smoldering rate and the relative amounts of radiative and conductive heat transfer. Then, based on the relative contribution of heat transfer modes, the heat flux and the total heat released were calculated with the fitted smoldering rate as a function of cigarette design parameters. Results show that the circumference of the cigarette is the major physical factor affecting mass burn rate (MBR), while the packing density of the cigarette strongly affects the linear burn rate...

High-speed Visualization of Flame Propagation in Explosions

Abstract: Flow visualization data is presented to describe the structure of flames propagating in methane-air explosions in semi-confined enclosures The role of turbulence is well established as a mechanism for increasing burning velocity by fragmenting the flame front and increasing the surface area of flames propagating in explosions This area increase enhances the burning rate and increases the resultant explosion overpressure In real situations, such as those found in complex process plant areas offshore, the acceleration of a flame front results from a complex interaction between the moving flame front and the local blockage caused by presence of equipment It is clear that any localised increase in flame burn rate and overpressure would have important implications for any adjacent plant and equipment and may lead to an escalation process internal to the overall event To obtain the information required to quantify the role of obstacles, it is necessary to apply a range of sophisticated laser-based, optical diagnostic techniques This paper describes the application of high-speed, laser-sheet flow visualization and digital imaging to record the temporal development of the flame structure in explosions Data is presented to describe the interaction of the propagating flame with a range of obstacles for both homogeneous and stratified mixtures The presented image sequences show the importance of turbulent flow structures in the wake of obstacles for controlling the mixing of a stratified concentration field and the subsequent flame propagation through the wake The data quantifies the flame speed, shape and area for a range of obstacle shapes

Further studies concerning the energy distribution in the ETC closed chamber and the impact on observed propellant burn rate

Abstract: In this paper, the authors investigate the consequences of the changing chemical equilibrium states that occur during ETC closed chamber experiments and the associated impact on the propellant burn rate calculation. The theoretical results are compared with experimental data to determine the influence on the computed propellant burn rate when a plasma is present.

Study on Low Burning Rate NEPE Propellant

Abstract: A low burning rate NEPE propellant were investigated by means of adding some burning rate inhibitors and adjusting its composition. The compatibility of additives with nitrite ester, combustion properties of the propellant and the standard specific pulse of Φ40 rocket motor were measured. It was observed that the burning rate of the propellant could be depressed by more bigger particle diameter AP , low ratio of NG/DEGDN, less AP content and presence of burning rate inhibitors. The burning rate under 4.0MPa could be 4.7mm/s, and standard specific pulse was 2239.3N·s/kg without additives.

Initiation of Chemical Reactions in Energetic Materials Using Plasmas and Arc Channels

Abstract: : Development of arc channels in propellant beds will lead to initiation of chemical reactions and possible ignition. Same initiation can take place with high-energy density plasmas generated by electrothermal plasma sources. Arc channels can be simulated via arc generators from as low as few milli-joules to several joules of energy. For electrothermal plasmas, the energy is in the range of few kilo-joules. When using electrothermal plasmas, the performance of the propellant is more governed by radiation transport and the plasma-flow-field parameters. The temperature of the propellant's bed may also play a role in the burn rates under plasma injection. In this report, a set of experiments were first conducted on the plasma-flow-field to determine the spatial and temporal distribution of the plasma temperature, pressure, number density, and velocity. The experiments revealed a decreasing plasma pressure, plasma temperature and plasma number density as plasma is leaving the capillary source and expands in air. The plasma jet velocity 2 inches from the source exit was found to be about 1300 m/s. Following characterization of the plasma-flow-field, a set of experiments were conducted on JA-2 solid propellant with controlled bed temperature. Increased burn rates were observed with increased bed. A model for the burn rate is proposed, which includes the bed temperature and has the BR = A P(sup a) (T/T(sub ambient))(sup b).

Effect of aluminium in propellant composition on acoustic emission parameters (Short Communication)

Abstract: The study reports the variation in acoustic emission signals acquired during combustion of typical propellants with varying aluminium and ammonium perchlorate content. It was observed that when propellant strands having the same composition undergo combustion under similar conditions, they produce consistent acoustic emission signals. To study the effect of variation of aluminium content in the propellant composition on the acoustic emission produced during combustion, the aluminium content was varied from 6 per cent to 18 per cent in a HTPB-based composite propellant with 86 per cent solid loading. Experiments were carried out with propellant strands under the same conditions for a comparative study. Acoustic emission parameters, such as peak amplitude, ring-down counts, average frequency, hits and energy were studied as functions of time. Among these parameters, only energy ring-down counts and frequency varied significantly with aluminium content. The effect of cumulative values of energy, frequency and ring-down counts, the effect of burn rate and theoretical specific impulse against the aluminium percentage variation, and the variation of specific impulse against acoustic energy can all be correlated. The clear trend is indicative of possible prediction of propellant performance parameter like specific impulse from acoustic emission parameters.