yeah me again, ," just doin a bit of readin" on bp burn rates, and it looks like( well to me anyway) this is what the text says, that with extra loading pressure of a composition in a tube this effects the efficiency of energy feed back by convective transfer, high loading pressure decreases the burn rate by decreasing gas permeability.
Interesting what do you mean by burn rate? Conclusion 1 taken from the document says:-
(1) An increase in compaction produces a decrease in the
linear burning rate (cmls) but an increase in the mass burning
rate (gis). Similar observations(28) led to the conclusion that the
rate-controlling reactions of black powder occur in the condensed
(i.e. liquid and solid) phase. The maximum reaction
temperature (1250 °C) is, however, sufficient to cause the sublimation
or vaporization of most intermediates and products.
Hence the same amount of powder will burn in a shorter time in a rocket motor.
Looking at figure 1 in the paper, it shows a difference in the temperature when burning a pressed or rammed powder. This graph relates to a binary mixture. It would have been interesting to see this analysis continued through the paper. As assuming the total sample size was the same the integral of the two lines on the graph would show that the total energy output was lower in the pressed sample. This is interesting because it would mean that a different reaction stoichiometry is occurring under these different preparation regimes.
It would also have implications for developed thrust in a motor (ideal gas law PV=nRT).
However it would appear later in the paper they say that the calorific value of the fuels is identical (pressed vs rammed). In which case given their other results you would expect the lines on the graph in figure 1 to be reversed.
[/list]so.. the extra pressure is not allowing a higher temperature to form in the motor therefore you dont get a hotter more efficient burn, hmm so an additive( metal powder) should give you a higher heat of reaction and more power, irregardless of press load?, ho made my first batch of sulfur-less bp rp riced in baby oil dissolved?/ mixed in a acetone carrier, and it makes a lovely fluffy comp that presses into a good firm propellant grain, vid soon,
It is pretty much certain that the addition of metal powders will increase the temperature of the burning fuel. There is a high possibility that it would increase the heat of reaction (this can be checked using heats of reaction / heats of formation tables), but I am not certain without checking. From experience it does make for a powder with more thrust (except in the case of course powders which create nozzle erosion and burn mainly outside the rocket body), but this is probably due to the higher gaseous volume due to the higher temperature (PV=nRT).
As usual I am looking forward to seeing videos of your next test motors.
Phew that was close.