4 ms·

Some argue that liquid nitrogen is a decent option for short range. It's cheap, can be contained in relatively low-cost tanks (compared to hydrogen, certainly),

Some argue that liquid nitrogen is a decent option for short range. It's cheap, can be contained in relatively low-cost tanks (compared to hydrogen, certainly), and can be refilled quickly. The LN2 doesn't actually burn. It's more like a steam engine, where the pressure from the vaporizing nitrogen drives pistons or turbines. The nice thing here is that the LN2 comes straight from the atmosphere and goes straight back into it. Net zero emissions from the car (obviously producing the energy to compress the nitrogen in the first place isn't going to be net zero, but that's basically the same issue as with hydrogen, electricity, or this ammonia system).

robryk 3y ago
That seems to have energy density lower than even batteries though. When you vaporize LN2, you apparently need 0.2MJ/kg of heat. The amount of mechanical energy you extract out of vaporizing that (when heat is provided by the environment) can't exceed the heat required to do so (because condensing the nitrogen back into LN2 is exothermic). Apparently current Li-ion batteries have ~250 Wh/kg = ~0.9MJ/kg energy density, which is significantly higher than the upper bound above. Am I mistaken somewhere?