Combustion Of Double-base Propellants Research Articles

Accounting for super-, plateau- and mesa-rate burning by lead and copper-based ballistic modifiers in double-base propellants: a computational study.

We present a first-principles computational study to understand the action of lead and copper-based ballistic modifiers in the combustion of double-base propellants (DBPs). We show that lead oxide clusters are easily broken down upon addition of small amounts of carbon and the resulting graphitic matrix, dispersed with weakly bound and exposed Pb sites, acts as a Lewis acid to bind small molecule Lewis bases such as NO2 and CH2O that form in the combustion flame. This accounts for super-rate burning, where the fuel burn rate is enhanced. We also show how carbon availability accounts for the plateau- and mesa-rate burning effects, where the fuel burn rate is suppressed. In contrast, cluster integrity on binding carbon to copper oxide is retained, and interaction with NO2 and CH2O is essentially negligible. Carbon binds more strongly to copper oxide, however, and we therefore propose that when carbon levels start to fall this results in the lead oxide clusters being starved of carbon, which leads to plateau and mesa burning. Taken together, the calculations support a general model that accounts for the super-, plateau- and mesa-rate ballistic modifier burning effects.

Study on the reaction mechanism of CH2O + NO2 transformed by PbO/SnO in double-base propellants through theoretical calculation and experiment

The reaction of CH2O and NO2 plays an important role in the combustion of double-base propellants, the mechanism about the influence of PbO (SnO) on this reaction is still unclear. In this paper, we obtained the product PbCH2O2 (SnCH2O2) through DFT calculations. After wavefunction analysis (MBO, LMOs, ESP et al.), we not only deeply understood the properties of PbCH2O2 (SnCH2O2), but also realized that the introduction of heavy metals (Pb, Sn) will greatly increase the van der Waals interaction and electrostatic interaction. The calculations of reaction thermodynamics and reaction kinetics indicated that PbO (SnO) can obviously reduce the Gibbs free energy barrier and increase the reaction rate. The burning rate shown the positive correlation with the results of thermodynamics and kinetics. The analysis of the combustion residue showed that the elemental Pb (Sn) produced on the surface, which may be related to the further decomposition of PbCHO2 (SnCHO2) and also reveal a transformation cycle of PbO(SnO)-Pb(Sn). The RSFT-IR analysis of the double-base absorbent powder not only proved that the existence of PbO (SnO) could reduce the decomposition temperature of the absorbent, but also indicated that the existence of PbCH2O2 (SnCH2O2) and PbNO2 (SnNO2). Combining with the theoretical calculations and experiments, we established a reaction process about the cyclic catalysis of PbO (SnO) in double-base propellants. And more importantly, the effect of the metals with higher density and larger radius in double-base propellants deserves more attention.

Effect of fluorine-containing nano-sized multi-functional additives on thermal decomposition behavior and gaseous products of double-base propellants

To study the effect of fluorine-containing nano-sized multi-functional additives on the thermal decomposition behavior and gaseous products of propellant, the thermal decomposition process and gaseous products of double-base propellants were studied by TGA/DSC-IR instruments. The high-pressure combustion of double-base propellants was conducted in a closed vessel, and the gaseous products were characterized by FT-IR spectroscopy. The effect of pressure, TiO2-trifluoroacrylate additives and temperature on the gaseous products was discussed. Results show that NO2 and NO gases were produced in the thermal decomposition rather than in the high-pressure combustion. The fluorine-containing nano-sized multi-functional additives do not affect the species of gaseous products of double-base propellants, but it decreases the concentration of CO toxic gas. Also, the thermal stability of double-base propellant is improved after the addition of TiO2-trifluoroacrylate additives. Furthermore, the FT-IR peak intensity of gaseous products was improved by increasing temperature in the temperature range 30–150 °C. Therefore, the application of fluorine-containing nano-sized multi-functional additives can reduce the damage of toxic gases on the environment and personnel.

Combustion of double-base propellants of various compositions containing ammonium nitrate

The combustion of various propellants containing ammonium nitrate (AN) is studied. It is shown that the effect of AN on the burning rate depends on the heat of combustion of the starting propellant, the amount of AN, and the pressure at which combustion occurs. Thus, AN slightly increases the burning rate of low-calorific value propellants and significantly reduces that of high calorific value formulations. It is shown that combined catalysts can considerably increase (by a factor of up to ≈6 at a pressure of 2–4 MPa) the burning rate of propellants containing 50–70% of AN, and reduce the pressure dependence of the burning rate.

Transient modes of double-base propellant combustion in a semiclosed volume

Experimental data on the transient combustion of double-base propellants in a semiclosed space are presented. The transient process is initiated by a sharp change in the cross sectional area of the nozzle. The pressure in the combustion chamber at various ratios between the initial and final cross sectional areas of the nozzle is measured. An attempt to explain the experimental data obtained within the framework of the phenomenological theory of non-steady-state combustion of energetic condensed systems is undertaken. A comparison of experimental and theoretical results demonstrates their satisfactory agreement.

Effect of Some Catalysts on Combustion of Double-Base Propellants

The effect of PbO2, SnO2, TiO2, and Bi on the combustion of propellants of various compositions is investigated. It is established that SnO2, TiO2, and Bi have a significant effect on the burning rate of propellants without carbon black and additional plastifiers. A marked catalytic effect of PbO2 is manifested only when its content is higher than 5%. It is shown that the addition of SnO2 and PbO2 to propellants leads to formation of a carbon black matrix on the burning surface, on which catalyst particles build up. With the addition of carbon black to propellants, the catalytic action of TiO2 and Bi is enhanced only slightly, and the effect of SnO2 at moderate pressures is markedly reduced due to a considerable increase in the degree of reduction of the active form of (SnO2) catalyst up to its inactive forms (SnO and β‐Sn).

Effect of RDX and HMX on the Efficiency of Catalysts for Double-Base Propellant Combustion

High explosives (RDX or HMX) are added to double–base propellant formulations to improve their energy characteristics. The influence of these HE on the catalysis of propellant combustion practically has not been discussed in the literature. The present paper considers the role of RDX and HMX in the catalysis of double–base propellant combustion. Propellants having various compositions and energy characteristics were studied experimentally. It is established that RDX and HMX decrease the burning rate of double–base propellants (without catalysts) with moderate and high calorific values irrespective of their effect on the energy and combustion characteristic of the propellants. It is shown that if the burning rate of a propellant is affected by catalysts, the addition of RDX or HMX to this propellant (in excess of 100%) does not decrease the relative efficiency of catalysis but even increases it somewhat.

HMX and RDX - Combustion mechanism and influence on modern double-base propellant combustion

Experimental investigations of the burning wave structures of HMX and RDX were carried out by microthermocouple technique at a pressure of 1-70 (90) atm. Burning-surface temperature, heat release in solid, heat feedback from gas to solid, and heat-release rate in gas near the surface were obtained. The data obtained show that in the condensed phase of combustion waves of nitramines, evaporation, and thermal decomposition occur simultaneously, with heat release in the solid being negative at p 5-10 atm. Activation energies of HMX and RDX decomposition in combustion waves were evaluated. Published results of investigation s of the thermal burning wave structures of double-base propellants (DBF) containing HMX and various catalysts were used to establish the influence of additional nitramines on the unified dependencies of simple DBFs. It was found that the gasification law, heat-release law in the solid, and heatfeedback law do not change, but that the dark zone laws and dependencies for temperature sensitivities change significantly when HMX is added.

The mechanism of lead catalysis of double-base rocket propellant combustion: Super-rate burning and the plateau/mesa phenomena

Although double-base propellants contain a fairly complex mixture of ingredients, the most unstable compounds present are the nitrate esters, nitrocellulose and nitrate ester plasticizers, which represent the majority of most formulations; usually the ballistic additives, a lead compound and often carbon, represent from 1% to 5% of the total propellant. Energetic additives such as RDX and HMX are often present, but these nitramines are less responsive to lead catalysis which is characterized by a region of super-rate burning at lower pressures followed by a plateau region at higher pressure as the catalytic effectiveness appears to decrease and often a mesa region as the burn rate actually decreases with pressure. To explain both the super-rate burning and the plateau/mesa phenomena, one should logically examine the chemistry of decomposition of the nitrate esters to explain both lead catalysis and the apparent loss of catalysis; fortunately, examination of the reported chemistry of nitrate esters and several more recent investigations, which used sophisticated experimental techniques to examine double-base propellant combustion, provide support for a comprehensive mechanism to explain both.

A model for double base propellant combustion

A model has been developed to describe the combustion of double base propellants with a primary objective to develop a better understanding of the combustion mechanisms of double base propellants in both condensed and gas phases. The gas phase in double base propellants sustains two flames which are separated by a dark zone at low pressure. At high pressure, the secondary flame merges into the primary flame, eliminating the dark zone. The proposed model calculates the temperature profile in both the condensed phase and through both flames of the gas phase. the model solves the energy equations and species equations for both the condensed and gas phases separately, and then matches the boundary conditions between the two phases. The model assumes that there are three parallel reactions occurring in the condensed phase; a zero order degradation reaction, a first order reaction with NO 2 , and a second order reaction of complex aldehyde species. The gas phase kinetics are summarized with four reactions; a first order NO 2 reaction, a second order reaction of aldehydes, a first order NO-carbon reaction, and a second order NO reduction reaction. p In the past, several models have been developed to predict the burning rate of double base propellant as a function of pressure and initial temperature. Increasingly numerous experimental results (most from Kubota and Zenin) provide a well established data base which, along with increased computing capability, now allow one to verify the reliability of numerical models using a much broader variety of experimental data. A complete model must determine the burning rate as a function of pressure and initial temperature. In this study, the behavior of each reaction zone through the propellant combustion wave has been examined.

ニトラミン化合物添加によるＣＭＤＢ推進薬の安定燃焼領域の拡大

The effect of nitramine addition on stable combustion of double-base propellants has been examined in order to lower the combustion limit of rocket motors. The nitramines tested in this study are RDX (cyclotrimethylene trinitramine) and HMX (cyclotetramethylene tetranitramine). These nitramines are used as the energetic materials to increase the specific impulse and are also used as the agents to decrease the burning rate of double-base propellants. It has been found that the addition of the nitramines acts to increase the heat of explosion at low pressures and to prevent an incomplete combustion of double-base propellants. Thus, the pressure exponent of the flame temperature decreases due to the increased flame temperature at low pressures. Consequently, the pressure of stable combustion limit of a double-base propellant rocket motor is lowered by the addition of nitramines.

Thermal decomposition studies of catalysed double base propellants

To understand the rote of lead salts of organic acids in the combustion of double base rocket propellants, thermal decomposition behaviour of propellants was studied bydta andtg methods. Catalysed propellants decomposed at lower temperatures than the control. Percent thermal decomposition of propellants containing lead salts was also higher. Rate constants were higher and energy of activation was lower for catalysed propellants. Results obtained suggest that condensed phase reactions may be the site for the action of lead salts in the combustion of double base propellants

Chemistry of combustion of double-base propellants through sliver analysis

Chemistry of combustion of double-base propellants through sliver analysis

A comprehensive erosive-burning model for double-base propellants in strong turbulent shear flow

A comprehensive aerothermochemical model of erosive burning of double-base propellants has been developed. The present analysis includes detailed modeling of the combustion process, taking into account both chemical kinetics and diffusion effects in the gas phase. Different reactions simulating the fizz zone and the final flame zone (including dark and luminous zones) are considered in the gas phase. The instantaneous governing partial differential equations are Favre averaged to take into account variable density effects. The turbulence modeling consists of a two-equation ( k-ϵ) turbulence closure model for the final Favre-averaged conservation equations. The set of governing equations is solved numerically. Predicted results compare well with experimental data of Burick and Osborn for a noncatalytic double-base propellant. Predicted temperature profiles in the boundary layer correctly depict the characteristics of double-base propellant combustion. The main mechanisms for augmentation of the burning rate is the increase in heat feedback caused by turbulence-enhanced reactions and transport properties in the fizz zone.

Influence of long metal wires on combustion of double-base propellants

There have already been quite a number of experimental studies and reports, such as Refs. [1] and [2], concerning the influence of long and short metal wires embedded in composite propellant grains by casting on propellant combustibility. However, there have been few reports on the influence of long metal wires embedded in homogeneous double-base and modified double-base propellant grains by continuous extruding on propellant combustibility. Studying the combustion of the grains of propellants with single or multiple long wires embedded by extrusion, we observed that either double-base propellants or modified doublebase propellants, especially with higher energy and higher density, are just as good as some composite propellants with resepet to ballistic performance. This paper discusses the influences of long metal wires embedded in homogeneous double-base and modified double-base propellant grains on their combustibility. The experimental data in this paper are taken from tests of five kinds of propellants given in Table 1. The burning rates of propellant strands, with a single long metal wire embedded by extrusion, are determined with a burner filled with nitrogen. The outer diameter of the propellant strands tested is 6 rnm, and the lateral surfaces of the strands are inhibited so that the burning can only take place at the ends of the strands. In Table 2, we list the burning rate, the ratio of burning rates, and pressure exponent of propellant B, with various embedded wires of diameter 0.18

Model for double-base propellant combustion

The Beckstead-Derr-Price (BDP) monopropellant model that was originally developed as a limiting case for composite propellants has been modified and applied to double-base propellants. The work was performed with the intent of applying the model to modern double-base systems of interest in rocket propulsion. Therefore, the model has been developed to predict burn rate as a function of pressure, initial temperature, and the double-base binder energy. The model has been compared to a set of experimental data covering a wide range of pressures, initial temperatures, and binder energy with excellent agreement. A comparison with 81 test conditions resulted in 96% of the predictions within ± 10% of the data and a maximum error of 12%. All of the calculated rates, sensitivities, and combustion parameters using the double-base model appear to be consistent with available experimental data. The quantitative predictions of the model varying pressure, initial temperature, and binder energy are considered a significant advance in the state of the art.

The Role of Impurity Particles in the Combustion of Double-Base Propellants

Abstract The thermo-mechanical effect on combustion behavior of incorporating inert impurity particles into double-base propellants is investigated. Burning rate and temperature profile measurements of propellants containing various amounts of aluminium oxide powders of different grain sizes indicate that the inclusion of inert impurity particles enhances the burning rate at low pressures, the effect diminishing with increase in pressure. A theoretical model is constructed, based on the assumption that the interfaces created by these particles provide internal burning surfaces which decompose following an Arrhenius relationship. The simple theoretical model predicts the trend of the experimental results, but cannot provide any insight into the contribution of the thermo-mechanical effect to the overall heat of condensed phase reaction in double-base propellants.