chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a natural science that covers the elements that make up matter to the compounds made of atoms, molecules and ions: their composition, structure, proper ...

, the burn rate (or burning rate) is a measure of the linear

combustion Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combus ...

rate of a compound or substance such as a candle or a

solid propellant A propellant (or propellent) is a mass that is expelled or expanded in such a way as to create a thrust or other motive force in accordance with Newton's third law of motion, and "propel" a vehicle, projectile, or fluid payload. In vehicles, the e ...

. It is measured in length over time, such as millimeters per second or inches per second. Among the variables affecting burn rate are pressure and temperature. Burn rate is an important parameter especially in the area of

propellants A propellant (or propellent) is a mass that is expelled or expanded in such a way as to create a thrust or other motive force in accordance with Newton's third law of motion, and "propel" a vehicle, projectile, or fluid payload. In vehicles, the e ...

because it determines the rate at which exhaust gases are generated from the burning propellant, which in turn decides the rate of flow through the nozzle. The thrust generated in the rocket of missile depends on this rate of flow. Thus, knowing the burn rate of a propellant and how it changes under various conditions is of fundamental importance in the successful design of a solid rocket motor. The concept of burn rate is also relevant in case of liquid propellants.

Measurement

One device for measuring burning rate is a V-shaped metal channel about 1–2 feet long wherein a sample is placed, with a cross-sectional dimension of approximately 6 mm or 1/4in. The sample is ignited on one end and time is measured until the flame front gets to the other end. Burn rate (typically expressed in mm/s, or in/s) is the sample length over time at a given pressure and temperature. For solid fuel propellant, the most common method of measuring burn rate is the Crawford Type Strand Burning Rate Bomb System (also known as the

Crawford Burner A Crawford burner is a device used to test burn rate (chemistry) of solid propellants. It is also known as a strand burner. A Crawford burner consists of a small pressure vessel in which a thin bar of propellant to be tested is mounted on a stand. ...

or Strand Burner), as described in MIL-STD-286C.

Characterization

A substance is characterized through burn rate vs pressure chart and burn rate vs temperature chart. * Higher burn rate than the speed of sound in the material (usually several km/s): "detonation" * A few meters per second: "deflagration" * A few centimeters per second: "burn" or "smolder" * 0.01 mm/s to 100 mm/s: "decomposing rapidly" to characterise it. However, there is difference in opinion in differentiating the three in absence of firm numbers at a given

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country a ...

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...

References

{{DEFAULTSORT:Burn Rate (Chemistry) Combustion Temporal rates

Measurement

Characterization

See also

References