Burning rates

Burning rate is strictly defined as the mass rate of fuel consumed by the chemical reaction, usually but not exclusively in the gas-phase. For the flaming combustion of solids and liquids, the burning rate is loosely used to mean the mass loss rate of the condensed phase fuel. However, these two quantities - mass loss rate and burning rate - are not necessarily equal. In general, 

Fundamentals of Fire Phenomena James G. Quintiere 2006 John Wiley Sons, Ltd ISBN 0-470 09113 4 

Factors that influence the burning rate of fuel packages include (1) the net heat flux received at the surface, q , and (2) the evaporative or decomposition relationships for the fuel. We can represent each as 

A crude, but effective way to deal with the complexities of transient burning and fuel package properties is to consider liquid-like, quasi-steady burning. By Equation (6.34), 

In this form, the energy needed to break the original polymer bonds to cause unzipping or volatilization with char is closer to values representative of noncharring solid polymers. Table 9.1 gives some representative values found for the heats of gasification. 

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Tensile yield strength, 103 lb in-2 Thermal Burning rate, mm min Coefficient of linear thermal expansion, 10 °C 50-90 0.5-2.2 50-90 50-80 50-60 10-13 Self- extinguishing 40-55 46... 

Tensile yield strength, 1Q3 lb in-3 Thermal Burning rate, mm min Not Not Not Not Not Self- Self-... 

Ignition, pressure, burning rate, and thmst characteristics over temperature range... 

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. 

Propellants with potassium perchlorate have relatively high burning rates (1.75 cm/s at 6.9 MPa (1000 psi) and 21°C) and high burning rate exponents (0.6-0.7). 

Propellants with ammonium nitrate have very low burning rates (0.01 cm/s). 

R. C. Strittmater, E. M. Wineholt, and M. E. Holmes, The Sensitivity of Double Base Propellant Burning Rate to Initial Temperature, MR-2593, BRL, Aberdeen, Md., 1976. 

D. W. Reifler, Tinear Burning Rates of Ball Propellants Based on ClosedBomb Firings, CR 172, BRL, Aberdeen, Md., 1974. 

K. Adas, A. Method of Computing Web for Gun Propellant Grains from Closed Bomb Burning Rates, memo report 73, Naval Powder Factory, U.S. Navy, Indian Head, Md., 1954. 

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