Rate of burning

ASTM D635, Test Methodfor Rate of Burning andj or Extent and Time of Burning of Self-Supporting Plastics in a Hori yontal Position, Vol. 8.01, ASTM, Philadelphia, Pa., 1991. 

Some materials may bum quite slowly but may propagate a flame rapidly over their surfaces. Thin wood paneling will burn readily, yet a heavy timber post will sustain a fire on its surface until it is charred, then smolder at a remarkably slow rate of burning. Bituminous materials may spread a fire by softening and running down a wall. Steel of course does not burn, but is catastrophically weakened by the elevated temperatures of a fire. PVC does not bum, but it softens at relatively low temperatures. Other plastics may not burn readily but still emit copious amounts of smoke. And some flammable plastics, such as... 

The coating penetrates into the base grain to some extent to give, in effect, a progressively increasing rate of burning as the grain burns away... 

Audrieth (Ref 3) patented the use of (SCN)X as a fuel in primers, ignition and fuze time trains (see Table below). A significant advantage of the invention for fuze time train useage over BlkPdr is the greater control evidenced in the rate of burning... 

As the blackpowder core of a safety fuse bums, it produces gases which must escape. At the same time the heat of the combustion melts the bitumen and plastic and thus produces side venting through the textile layers. This results in the production of an increased but constant gas pressure, determined by the equilibrium between gas generation and gas lost sideways. As the rate of burning of blackpowder depends markedly on the pressure, it is this process of equilibration which determines the speed of burning of the fuse. 

It follows also that the actual rate of burning of safety fuse depends on the ambient pressure. Indeed, if the pressure is reduced to less than about a fifth of an atmosphere the burning ceases altogether. In deep mines the extra pressure can be sufficient to give an increase in burning speed of safety fuse. Compared with the effect of pressure other influences on the burning speed are small. Temperature has little effect and humidity also has little effect unless the fuse is kept for a prolonged period at a humidity sufficient to cause deliquescence of the potassium nitrate in the core. 

It was shown by Vieille that the rate of burning, R, of blackpowder depends exponentially on the pressure,p, by the following equation ... 

It is found that the rate of burning increases approximately linearly with the calorimetric value and lies in the range 0-4—1-3 cm s I at 7 MPa, although higher rates can be achieved. 

The results of measurements made in these ways show that the rate of burning of a propellant depends markedly on the pressure. At the high... 

The rate of burning of a propellant is also influenced by the initial temperature of the charge. The effect is much less than the normal effect on chemical reactions, but can still be important when the material is to be used over a wide range of temperatures from arctic to tropical and those encountered in supersonic flight. 

For some purposes, it is indeed desirable that the rate of burning should increase during the process rather than remain constant. This is true in certain guns. For such purposes grains can be produced perforated by a number of holes so that the burning surface increases as combustion proceeds. For rockets special constructions are used which are discussed in Chapter 19. 

Moderated. In propellants, implies the presence of a surface coating to the grain which slows down the initial rate of burning. 

Time fuse, or safety fuse, which is used in most nonelectric firing systems, is available in a multitude of varieties, both in color and rate of burning. 

Ignition sources of BS 5852 Parts 1 and 2 Theoretical heat of combustion approx. Flame height Flame temp. Local heat flux. Rate of burning Duration of flaming ... 

RATE OF BURNING AND USE OF IGNITION TESTS TO DEFINE FLAMMABILITY... 

In an ideal situation the parameters used to define furniture should be ignition resistance and the rate of generation of heat, smoke and toxic gases. Tests to do this with actual or mock-up full sized furniture are not yet available as final specifications but the Nordtest (28) and NBS furniture calorimeters (29) represent scientific methods while room/ corridor rigs, typically UK DOE PSA FR5 and 6 of 1976 (5) (6) were originally used but are less satisfactory from a scientific point of view. The Californian (30) and Boston tests (31) for public area furniture are essentially simple room tests and are similar in principle to DOE, PSA, FR5 and 6 although the latter do not have pass/fail criteria. Bench scale rate of heat release tests include the NBS cone (29) which, with a code of practice represent a possible alternative but the rate of burning of... 

Since at y = 0, the mass flux pv is the mass loss rate of burning rate evolved from the condensed phase. From Equation (9.18) we also realize that we have a constant pressure process... 

It is relatively straightforward to develop the controlling parameters of a stirred reactor process. If ip is defined as the unbumed mass fraction, it must follow that the fuel-air mass rate of burning RB is... 

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