Strand burning rate determination

If the gases are continually flowing out, as in the case of a rocket motor, the pressure remains almost constant thruout the combustion period. The linear burning rate and its variation with temp and pressure can be determined in a Crawford type strand burning rate bomb. The temp coefficient of the burning rate is the variation per degree of temp increase at constant pressure, The dependence on pressure is characterized by the pressure exponent... 

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. 

Burning Rates of Propellonts Experimental Techniques. Burning rates of gun propellants are usually determined in closed bombs (vessels), while for rocket proplnts the strand burning apparatus is used. Both methods are described in Vol 3 ">f Encycl, under Closed Bomb , pp C330 to C335, Figs on pp C333... 

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. 

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