Strand burner

Rocket propellants must not contain sizable cracks, pores, or cavities. They are inspected using x-rays and ultrasonics, and firings are conducted in strand burners, intermpted burners, and in reduced or full-scale rocket motors (see also Nondestructive evaluation) (16—20). 

Experimental Determination of the Burning Rate. Experimental determinations of the burning rate are made with the closed tomb for gun propellants and the strand burner for rocket propellants. The closed bomb is essentially a heavy-wahed cylinder capable of withstanding pressures to 689 MPa (100,000 psi). It is equipped with a piezoelectric pressure gauge and the associated apparatus requited to measure the total chamber pressure, which is directly related to the force of the propellant. It also measures the rate of pressure rise as a function of pressure which can then be related to the linear burning rate of the propellant via its geometry. Other devices, such as the Dynagun and the Hi—Low bomb, have also been developed for the measurement of gun propellant performance. 

The strand burner is a bomb pressurized with an inert gas-to-rocket pressure and equipped with auxiUary apparatus consisting primarily of electrical... 

Fig. 5.7 shows scanning electron microphotographs of a TAGN surface before combustion (a) and after quenching (b). The quenched surface is prepared by a rapid pressure decay in the strand burner shown in Appendix B. The quenched sur-... 

In an attempt to understand the combustion mechanism of catalyzed double-base propellants, several investigators have conducted experiments to measure the burning rates of strands of liquid nitrate esters. The various measurement techniques were very similar to that employed in a conventional solid propellant strand burner. The liquid esters were placed in a tubular container, and the liquid surface regression speeds were measured by optical methods or by the fuse-wire method used in solid-propeUant strand burners. The only important difference between the solid and the liquid strand burning-rate measurements is that the liquid strand burning speed is very much dependent on the diameter of the container. 

Figure E-1. Chimney-type strand burner with observation windows.

Low-frequency oscillation in a rocket motor depends on the pressure exponent of propellant burning rate and the free volume of the chamber. [ -7] when a double-base propellant composed of nc(0 510), ng( - 55), and dep(0.120), with pbsa(0.015) as a platonizing catalyst, bums in a strand burner, the burning rate characteristicsmay be divided into four zones, as shown in Fig. 13.14. The pressure exponent varies between the pressure zones n = 0.44 in zone I above 3.7 MPa, n= 1.1 in zone II between 3.7 MPa and 2.1 MPa, n = 0.77 in zone III between 2.1 MPa and 1.1 MPa, and n = 1.4 in zone IV below 1.1 MPa. 

The burn rates of propellants are determined in a strand burner (Crawford bomb/ acoustic emission technique) at various pressures using an inert gas for pressurization. This data, when fitted in the empirical relation r = a.P" provides the pressure index n and the coefficient a. This technique is highly useful as a first approximation and is extensively used for propellant screening and quality control. The bum rates at different pressures are also determined by static testing in a ballistic evaluation motors (BEMs) and burn rates are typically scaled up from 1-5% for full scale motors. 

A series of tests were conducted by the Ballistic Research Laboratory at the APRFR which ranged from developing techniques and methods of irradiating burning miniature rocket motors and strand burners from outside to inside the reactor core (in the glory hole) (Refs... 

The neutron dose increased from 1012 n/cm2 to 3 x 1014 n/cm2 in the glory hole. SPRINT-type solid rocket propints containing NC, NG, AP, HMX and A1 were irradiated without any effects in strand burner and motor burning configurations taking into consideration the safety features required for this type of expt... 

By having a surge tank attached to the strand burner, only a very slight pressure rise occurred as a result of the burning of the strand. Consequently, burning occurred at essentially constant pressure. This method has also been adopted for use with strands which have been cut from sheet proplnt and even strands sliced from sections of cast grains. Fig 1 shows a typical strand burner assembly... 

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