The flame propagation into a narrow gap, which is prepared perpendicular to the prime burning surface of solid propellant grain, has been experimentally investigated using the test specimens of polyester-ammonium perchlorate composite propellants. Experimental results show that the flame propagates from the original burning surface into a gap when its width is larger than some critical value, and vice versa. This means that there always exists the critical value for the width of gap which is the threshold of propagation and nonpropagation of flame into it. The critical value is primarily the function of linear burning rate and the over-all mechanism of flame propagation into a gap of solid propellant grain will be explained with the quenching theorem. It is expected that further work will give a useful measure to the setting of standards of nondestructive testing of solid propellant grains and motors. (Author).

The flame propagation into a narrow gap, which is prepared perpendicular to the prime burning surface of solid propellant grain, has been experimentally investigated using the test specimens of polyester-ammonium perchlorate composite propellants. Experimental results show that the flame propagates from the original burning surface into a gap when its width is larger than some critical value, and vice versa. This means that there always exists the critical value for the width of gap which is the threshold of propagation and nonpropagation of flame into it. The critical value is primarily the function of linear burning rate and the over-all mechanism of flame propagation into a gap of solid propellant grain will be explained with the quenching theorem. It is expected that further work will give a useful measure to the setting of standards of nondestructive testing of solid propellant grains and motors -- Author.

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Future direct-fire gun systems will require solid propellant at high loading density, which can be achieved with propellant in slab-type geometry such as radial discs, concentric wraps, or scrolls. Adjacent propellant slabs will form porosity as narrow sheet-like channels (with entirely different permeability than bundled sticks or cylindrical grains). Successful functioning of the charge requires rapid ignition and unimpeded flame propagation throughout this system of channels. The present investigation is concerned with characterizing the fundamental ignition and transient combustion behavior of energetic materials when packed in such configurations. A special laboratory apparatus was designed to isolate two propellant channels and allow direct comparison of the influence of variable gap width, wall composition (inert or JA2 here), and channel end closure. Diagnostics include multiple pressure time histories along each channel length and high-speed cinematography of the propagation of flame. Results are presented for several channel configurations, showing influence of JA2 or plastic wall material, gap widths of 0-0.89 mm, and channel downstream ends either open or closed.

A one-dimensional theoretical model, incorporating the Noble-Abel dense gas law, has been developed to describe the transient model combustion phenomena inside a propellant crack. The theoretical model can be used to predict wave phenomena, heat transfer from the gas to the propellant surface and associated thermal penetration, flame propagation, and resultant pressurization at various locations along the propellant cavity. Calculations made with the current theoretical model revealed that the internal pressurization rate, pressure gradient, and flame velocity in propellant cracks (for which gases can penetrate) decrease as: the gap width increases, the rocket chamber pressurization rate decreases, and the propellant gasification temperature increases. Additionally, the predicted flame spreading was found to decelerate in a region near the crack tip; this phenomena has been experimentally observed by others.