Black powder burning

Figure 2.1 Influence of pellet density on black powder burning time.

To calculate the number of moles of gas produced per gram of black powder burned,... 

When black powder burns, the first portion to receive the fire undergoes a chemical reaction which results in the production of hot gas. The gas, tending to expand in all directions from the place where it is produced, warms the next portion of black powder to the kindling temperature. This then takes fire and burns with the production of more hot gas which raises the temperature of the next adjacent material. If the black powder is confined, the pressure rises, and the heat, since it cannot escape, is communicated more rapidly through the mass. Further, the gas- and heat-producing chemical reaction, like any other chemical reaction, doubles its rate for every 10° (approximate) rise of temperature. In a confined space the combustion becomes extremely rapid, but it is still believed to be combustion in the sense that it is a phenomenon dependent upon the transmission of heat. 

Black powder burns to produce a dense white smoke which contains extremely small particles held temporarily in suspension by the hot combustion gases. 

If dry and in good condition, black powder burns rapidly, especially in small grain size, with a yellow or pinkish-blue flame and dense smoke. 

Black powder burns v/ith a great burning rate even at 1 atm. This allows us to fire a shell in a loose mortar in spite of little clearance between the shell and the mortar.With a smokeless powder,which burns only quite slowly below 1 atm, we cannot fire the shell unless we use a thick and heavy mortar and close the clearance entirely to raise the interior pressure to allow the smokeless powder to burn quickly, but it is not practical. 

Brownish-black powder burns to Sn02 on heating in air. d 6.45. fnsol in water or alcohol sol in acids, in coned sodium or potassium hydroxide solns. 

The functional relationship between pressure and Black Powder burn rate is shown below [Conkiing]. 

The burn rate of compacted Black Powder is about 0.5 cm/s. However, granular Black Powder burns at about 60 cm/s in the open [Urbanski] or at about 1000 cm/s if confined as above [Kosanke]. 

Naturally, none of the equations above are the only reactions occurring when black powder burns, but it is interesting that the equations reveal mechanisms for shifting the gas volume produced, and shifting the energy released when this old mixture is burned at different conditions. It was this ability to shift chemistry that made the development of firearms possible. Black powder does not shift from one equation to another like a transmission shifts gears. It s a smooth continuum of changing chemical reactions that has made this mixture a very versatile composition for centuries. 

Black powder burns basically according to the following empirical formula [1]... 

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