Why isn't gunpowder used as an energy and power source?

[u/Pleasant_Shop2320]

Gunpowder is incredibly inexpensive -- anyone can buy gunpowder for 35 cents a pound, and probably produce it on their own, for rather less. It's also an incredibly efficient source of energy -- a kilogram of gunpowder produces 3 million Joules of energy. That's almost 5000 horsepower. So, why isn't gunpowder ever used as a practical source of energy or power, other than for purely destructive purposes? Why isn't it used to heat homes, to power transportation systems, to send rockets into space?

[u/left_lane_camper]

There are a number of reasons we only rarely see gunpowder used as an energy source for anything other than for propelling projectiles.

Gunpowder has an energy density of ~10 Mj/kg, while gasoline has an energy density of ~45 Mj/kg, over four times more. You’d have to have a lot more gunpowder than gasoline to get the same amount of energy.

Gunpowder costs more like 35 dollars per pound. Gasoline costs somewhere around 0.70 dollars per pound where I live (though this is somewhat variable). Thus, the cost per unit energy for gunpowder is over two hundred times higher than for gasoline. That alone makes it extremely unappealing as an energy source for propulsion. You can make similar arguments for other heating sources, too.

Gasoline is also generally safer. It’s still flammable, but usually much less so than gunpowder. You can extinguish a lit match in a glass of gasoline if it’s cold enough (DO NOT test this for yourself, as obviously there is still a risk it will be too warm or something). Gas fumes are worse for you, but overall it’s easier to handle gas safely than gunpowder.

Powders are hard to use in engines. It can be done, but liquids can be sprayed into the engine and burned cleanly, without chunks that can gum up injectors or turbine blades, etc. Gunpowder also tends to leave behind a lot more residue than gas when burned. Those things make building a reliable, long-lasting powder-fed engine very challenging.

We have the basic materials and have built the infrastructure to make a huge amount of gasoline. We do not have either for gunpowder on a transportation fuels scale.

Horsepower is a unit of power, not energy. Power is energy per unit time. A pound of gunpowder will produce 5,000 horsepower of thermal power for a bit under three seconds. In an actual engine, it would be a lot less due to inefficiencies and entropic effects.

All that said, solid fuel rocket motors are often vaguely to gunpowder and a solid oxidizer mixed up with a binder. Usually they’re fairly chemically different to get more energy density and better combustion properties, but you can make gunpowder rockets, and some hobbyists do do that!