Is there a limit in physics/chemistry I need to change by inventing Unobtainium? Or is it just a matter of economy by making regular fuel much harder to extract, and chemical explosives much commonly available?

If using TNT/C4 for civilians cars is still to expensive/unreliable/dangerous, what about specialized military hardware where cost isn't too much a concern compared to having mech/ubertank?

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    $\begingroup$ High speed explosives like TNT explode faster than the speed of sound, generating a bigger-than-usual pressure wave. It would severely damage the combustion chamber (i.e. instantly blow out the head gasket). Plastic/ powder explosives also can't get sucked into the chamber like liquid/ gas fuels so the self-sustaining internal combustion process wouldn't work at all. $\endgroup$ Jan 3, 2017 at 3:25
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    $\begingroup$ Mythbusters tried to do this with black powder. They were not successful. $\endgroup$ Jan 3, 2017 at 4:16

2 Answers 2


Two points:

Regular fuel is an explosive after being run through a carburetor or fuel injector. Read about fuel-air bombs (aka thermobaric weapons).

We use petroleum as the feedstock for manufacturing C4 and TNT. You're going to need a different history of organic chemistry to make this work.


Won't work. It is thermodynamics and physical chemistry.

Combustion is not an explosion it is a (fast) burn. I have a degree in chemical engineering and a burn is mass transfer limited. Oxygen and fuel must come in contact and the fuel is oxidized producing heat. Efforts are made to slow down the burn rate so it does not complete before the cylinder gets to the bottom. Lead was great for slowing burn rate. Super is slower burn. Ping is when the gas vapors burns too fast.

On an explosion the elements are already in contact and you are only limited by kinetics.

Basically an explosion is too fast for a thermal engine. Now you may invent an engine other than a thermal. A thermal engine means not harnessing the energy directly. Rely on PVT (pressure, volume, temperature) properties to push the cylinder.

  • $\begingroup$ I know that this is just arguing semantics, but stating that combustion is too limited to be considered an explosion is just a matter of point of view. It is fully possible to consider a combustion to be a very controlled explosion provided that the material can undergo a more rapid, uncontrolled version, which gasoline can (see the thermobaric link in John Feltz answer). I'm not after an argument over the definition of explosion, just to point out that the PoV and choice of fuel makes a difference (this was discussed when I studied chem. engineering). You are still correct; +1 for your answer $\endgroup$
    – Mrkvička
    Jan 3, 2017 at 8:30

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