the difference between combustion and explosion is the speed of the reaction.
what is the difference between combustion and explosion?
the speed of the reaction
the speed of the reaction is what distinguishes an explosive reaction from an ordinary combustion reaction. unless the reaction occurs very rapidly, the thermally expanding gases will be moderately dissipated in the medium, with no large differential in pressure and there will be no explosion. consider a wood fire. as the fire burns, there certainly is the evolution of heat and the formation of gases, but neither is liberated rapidly enough to build up a sudden substantial pressure differential and then cause an explosion. this can be likened to the difference between the energy discharge of a battery, which is slow, and that of a flash capacitor like that in a camera flash, which releases its energy all at once.
explosion
the pyrophone is similar to the steam calliope, but the difference is that in the calliope the combustion is external to the resonant cavity, whereas the pyrophone is an internal combustion instrument. the difference initially seems insignificant, but external combustion is what gives the calliope its staccatto. operating under the constant pressures of an external combustion chamber, the calliope merely directs exhaust (hb# 421.22: internal fipple flutes). by controlling the combustion specific to each resonant chamber, the pyrophone has, for better or worse, a greater range of variables in play when producing tones. in a purely mechanical (non-solenoid) calliope, the resulting pressures of external combustion result in between of trigger pressure. in a mechanical pyrophone, trigger weight per key is related to comparatively lower backpressure of combustible gas. again, the force of combustion happens in the resonance chamber; rather than controlling the exhaust of an explosion that has already happened in order to produce tones, the pyrophone controls the explosion to produce the tone.
pyrophone