Ignition Of Composite Propellants Research Articles

Effect of the thermophysical properties of the material of a local energy source on conditions and characteristics of ignition of metallized composite propellants

Solid-phase ignition of metallized composite propellants by a single particle heated to a high temperature under conditions of an ideal thermal contact has been numerically studied. The effect of the thermophysical properties of the material of a local energy source on the conditions and characteristics of ignition of composite propellants has been analyzed. It has been found that sources with a high heat storage capacity exhibit shorter ignition delay times for metallized propellants (by 10–60%) and lower initial temperatures required to initiate the combustion process (by 170 K). In addition, it has been found that the presence of particles of metals (boron, aluminum, magnesium, lithium) in the propellant composition leads to an increase in the effective thermal conductivity of the propellant. The cumulative effect of the thermophysical properties of the materials of the “particle heated to a high temperature–metallized composite propellant” system leads to an increase in the ignition delay times (by 25–65%) and the heat penetration depth of the near-surface layer of the propellant (by 25–40%) at the time of combustion initiation compared with metal-free compounds.

Three-dimensional simulations of ignition of composite solid propellants

This paper reports three-dimensional direct numerical simulations of ignition of a composite AP (ammonium perchlorate)–HTPB (hydroxyl-terminated polybutadiene) propellant subjected to a constant flux ϕ. The model includes solid heat transfer, gas-phase combustion with global kinetics and explicit description of propellant microstructure. Simulations show that ignition starts from AP particles because of primary AP/binder flame. Go/no-go computations reveal an unreported intermediate regime between go and no-go with apparent quenching followed by a delayed ignition. This delay is linked to a slow flame spreading from localized scattered hot spots on surface. In accordance with experiments, ignition delays deviate from classical ϕ−2 scaling for high flux and low pressure conditions. For intense flux levels, simulations attest deradiation extinction upon flux termination meaning that there is a critical flux above which ignition is no longer possible. The role of AP particle shape and size distribution on ignition delay is studied and predicted to be limited. The effect of propellant surface conditions is also investigated and can lead to substantial effects on ignition delay. Finally, semi-transparent propellants are also considered and low absorption materials result in longer ignition times, reduced ϕ-dependence, and absence of deradiation extinction. This work eventually highlights the importance of microstructure-based details in the physics of composite propellant ignition and opens the way towards better understanding of the role of AP particles.

Characteristics of composite propellant ignition by a CO2-laser

The delay time of ignition of a composite propellant based on ammonium perchlorate by a CO2-laser is measured at various pressures and radiant flux densities. The characteristics of the propellant at the moment of ignition are calculated. The obtained rate constants of the reactions in the propellant are compared to the respective rate constants of the reactions in the c-phase occurring during the combustion of the composite propellant.

Composite Propellant Ignition and Extinction by CO2 Laser at Subatmospheric Pressure

Composite Propellant Ignition and Extinction by CO2 Laser at Subatmospheric Pressure

Composite Propellant Ignition and Extinction by CO2 Laser at Subatmospheric Pressure

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A comprehensive model for AP-based composite propellant ignition

A comprehensive model and numerical solutions for ignition of AP-based composite solid propellants are presented. The analysis simulates the ignition process of a propellant sample, located in a stagnation region, under rapid pressure loading conditions. Specific features considered in the model include: 1) detailed chemical kinetics information for the ignition of AP-based composite propellants, 2) two-dimensional (axisymmetric) geometry for the composite propellant, and 3) rapid pressurization of the gas phase. An implicit finite difference scheme is used to solve the set of transient, second-order, coupled, inhomogeneous, nonlinear, governing partial differential equations. Numerical solutions reveal a number of important events occurring during the ignition sequence, including: igniter gas penetration to the region near the sample surface, combustion of unburned species upon arrival of compression waves, heat transfer to the propellant, pyrolysis of the oxidizer and fuel, and gas-phase reactions leading to ignition. The model correctly predicts the experimental observation that the ignition delay time decreases as the pressurization rate is increased. The various ignition criteria considered show the same trend as that measured experimentally.

Ignition of composite propellants in a stagnation region under rapid pressure loading

Ignition of AP-based composite solid propellants located at the tip of an inert crack wasinvestigated both experimentally and theoretically. The ignition process was observed by simultaneously using a high-speed (≈40,000 pictures/s) camera and a fast-response photodiode system. Heat flux to the propellant surface was measured with a thin-film heat-flux gage. Effects of pressurization rate, crack-gap width, and igniter flame temperature on the ignition process were studied experimentally. Experimental results indicate that the ignition-delay time decreases and the heat flux to the propellant surface increases as the pressurization rate is increased. Results of the theoretical analysis which employed separate solid-phase energy equations for fuel and oxidizer and the measured heat flux to the propellant surface are in good agreement with experimental data. The decrease in ignition delay with increasing pressurization rate is caused by enhanced heat feedback to the propellant surface at higher pressurization rates. This augmentation in heat feedback to the propellant at higher pressurization is believed to be a result of a combination of the following mechanisms: heating due to compression-wave reflection at the closed end; heat release due to burning of unreacted igniter species near the tip, behind the compression wave; and enhanced heat transfer due to recirculating hot gases near the tip.

Ignition of composite propellant at subatmospheric pressures by means of carbon dioxide laser

AbstractIgnition behavior of solid propellant composed of 25 wt% polybutadiene and 75% ammonium perchlorate under subatmospheric conditions has been studied using a carbon dioxide laser whose radiant flux is uniformalized. Data of ignition time in Ar, N2 and He atmospheres, and critical radiant flux and pressures over which ignition might be achieved, were obtained. Moreover, the data were compared with theoretical values, taking account of variable heat conductivity for the ambient gases with a surface ignition hypothesis.It is concluded that these ambient gases participate in the pre‐ and post‐ignition reactions and the ignition preventive behavior of He atmosphere is not predictable merely based on its high transport properties. The detailed observation of the ignition transient near the critical pressure revealed that the ignition in Ar atmosphere occurs in gas phase under less than 100 torr whereas in He atmosphere it occurs always at the condensed phase surface.

Ignition of composite propellants by low radiant fluxes

The ignition characteristics of several composite propellants subjected to blackbody thermal radiation were experimentally determined. Surface heat fluxes ranging from 1 to 13 cal/seccm were employed, and the effects of surface flux, initial propellant temperature, pressure, and surface geometry on the propellant ignition times were determined. Ignition tests on propellants formed by pressing ammonium perchlorate with nonvolatile carbon black and graphite showed that the surface ignition temperatures of these materials were the same as for normal propellants. A simple ignition theory is proposed which postulates that the ignition is controlled by a single surface reaction. The characteristic constants for this reaction (activation energy, etc.) may be determined from the effect of surface heat flux on the experimentally measured ignition times. Once the characteristic constants of the surface reaction are known, predictions of the variations in ignition times for changes in initial propellant temperature, pressure, and surface geometry are possible for flux levels in the range investigated.