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Multiple-chamber artillery can launch a projectile with energies much higher than single-chamber guns. I'm interested in setting a fundamental upper bound on the energy that a chamber (of a known volume) can impart to a projectile. This would, for example, set a limit on the needed volume for a sub-orbital gun (given a projectile mass). Since the pressure drop-off (like with single-chamber) isn't a constraint, the kinetic energy would be theoretically limited by pressure times volume. But you can't possibly achieve infinite pressure with any chemical reaction.

For that limit, some sources claim that pressures of 60,000 psi can be achieved. Coming from a physics perspective, I understand that a reaction should have a defined energy associated with an individual molecular transition. We've had related questions on physics stack exchange, but my thinking is that chemical equilibrium may be be a necessary tool.

If we ignore reaction kinematics, I believe that the maximum pressure that a reaction can achieve is limited by two things:

  • the density of the reactants before reaction and
  • the energy of the reaction

Given this, we could simply model the reaction with ideal gas assumptions, resulting in simple algebra. But I think this is wrong. Higher pressure would push the reaction to incomplete combustion. From a chemistry perspective, is there any theoretical maximum pressure that we could restrict all combustion reactions to?

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  • $\begingroup$ Maximising the pressure probably isn't a good idea to maximise the energy imparted to a projectile. This isn't a chemical constraint but a physical one: if the pressure is too high the gun barrel bursts. Real projectile weapons rely on explosives that deflagrate (basically the pressure wave travels through the explosive slower than sound) as this allows sustained pressure on the projectile over time rather than a big bang. $\endgroup$ – matt_black Jan 27 '16 at 19:29
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According to New Energetic Materials, table 1.2, a list of explosives ranges from 19-48 GPa in pressure achieved. This is two orders of magnitude greater than the 60,000 psi figure.

As far as maximum theoretical pressure, the question isn't really clear whether the maximum absolute pressure at which combustion can occur or the maximum change in pressure due to combustion is the value of interest. The answer could be related to the maximum pressure at which chemical bonds exist.

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