This paper presents an overview of ammonium perchlorate (AP) based propellant ignitability. A CO2laser provided the radiantenergy source. Neat AP ignition was performed on both production grade and high purity AP. The material was di©cult to ignite under the conditions. Five nonmetallized and sixteen metallized AP based formulations were

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Radiant ignition studies of ammonium perchlorate based propellants

Unsteady effects are introduced into the heat loss theory of low-pressure extinction of solid propellants to improve the prediction by the steady-state analysis. These effects include dynamic extinctions induced by the natural flame oscillation and by the forced flame vibration in response to external pressure disturbances. The analysis shows that a part of the steady-state solution at low pressure is linearly unstable and so it cannot be physically observed. In the linear stable region, flames that are close to the neutral stable point can still be quenched easily by a finite amplitude external pressure disturbance. The critical magnitude of this disturbance is computed in an approximate way. Both effects broaden the nonflammable range of the propellants.

Unsteady effects on low-pressure extinction limit of solid propellants

There were many studies on ammonium perchlorate (AP) based solid rocket propellant (SRP) and some data already exist. However, there is no complete data available in Malaysia especially the information on the combustion characteristics of baseline data of AP based SRP. This thesis discusses on the combustion characteristics of AP based SRP including the methods of the propellant selection and fabrication, burning rate test and static thrust test. Together with literature study and theoretical performance, thirteen sets of different propellant mixture were finalized with consideration of the mechanical and processability factors. The propellant was a mixture of AP as an oxidizer, Aluminum (Al) as fuel and Hydroxy-Terminated Polybutadiene (HTPB) as binder/fuel. For each mixture, HTPB binder was fixed at 15% and cured with Isophorone isocyanate (IPDI) (9.33% per mass of HTPB). The percentage of the solid materials was set at a constant value of 85%. By varying the AP and Al, the effect of oxidizer-fuel (O/F) ratio on the whole propellant can be determined. The propellant strands were manufactured using press-molding method and burnt in the strand burner at ambient pressure to obtain the initial burning characteristics. Then four propellant compositions were selected, namely p60, p66, p74 and p80 for further evaluation over a range of pressure from 6 atm to 31 atm. The results show that the increasing of O/F ratio and combustion pressure lead to the increase in burning rate. The fastest burning rate achieved was 12 -1 mmsec at combustion pressure of 31 atm for propellant p80 which has O/F ratio of 4.0. It was found that, the formulated propellant in this study have the normal burning characteristics with pressure exponent lies within the range of 0.501 to 0.561. Based on theoretical evaluation, formulation for p66 gives highest specific impulse, sp I . Thus, p66 has been selected to be evaluated in static thrust testing to obtain its performance characteristics. The results showed that the maximum thrust obtained is 162 N with generating sp I of 143.92 sec

Combustion characterization of ammonium perchlorate based solid rocket propellant

: A comprehensive theoretical model has been formulated for studying the degree of vulnerability of various solid propellants being heated by hot spall fragments. The model stimulates the hot fragment conductive ignition (HFCI) processes caused by direct contact of hot inert particles with solid propellant samples. The model describes the heat transfer and displacement of the hot particle, the generation of the melt (or foam) layer caused by the liquefaction, pyrolysis, and decompression of the propellant, and the regression of the propellant as well as the time variation of its temperature distributions. To partially validate the theoretical model in the absence of the necessary chemical kinetic data, an ice-melting and evaporation experiment was designed and conducted. These experiments provide features of the conductive heating, melting, and evaporating process. Calculated results compare well with experimental data in temperature-time traces, spall particles-sinking velocity, and displacement.

Modeling of Hot Fragment Conductive Ignition of Solid Propellants With Applications to Melting and Evaporation of Solids

: Laboratory ignition and combustion data have been compiled for Hazard Division (HD) 1.1 and 1.3 substances. These data can be used to identify their hazards potential with respect to a thermal threat. In general, the ammonium perchlorate (AP) based HD1.3 substances are easier to ignite at low pressure than the HD1.1 substances, such as nitramine-based explosives. Burning rate as a function of pressure and initial temperature has been illustrated for samples of HD1.1, 1.3, and 1.6, Extremely Insensitive Detonating Substances (EIDS). Convective combustion has also been illustrated. The effect of burning rate on friability data was illustrated for the three HD substances. Accounting for the effect of burning rate is necessary in order to quantify damage levels.

Ignition and Combustion Studies of Hazard Division 1.1 and 1.3 Substances

: Studies were directed at developing an understanding of mechanisms of propellants burning in air and of factors that control limits of burning so that one may rationalize choices of propellant formulation, charge configuration, process techniques, and special additives to reduce accidental ignition and burning of propellants in ambient air. Propellants were categorized in terms of convective, conductive, and radiative ignition data and in terms of burning rate and extinguishment limit data. Significant improvements in the flammability limits have been achieved using coolants (at the 10% level) with composite propellants made from high decomposition-temperature ingredients (e.g., HMX and polyurethane).

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L. H. Caveny

Papers

Solid Propellant Flammability Including Ignitability and Combustion Limits