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Comment by csours | Hacker News Reader

It's an interesting discussion, because if you assume access to atmospheric oxygen, gasoline is MUCH more energy dense.

    TNT.....:  4 kJ/gram and  7 MJ/liter
 
    Gasoline: 43 kJ/gram and 33 MJ/liter

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The previous point is fair though. What is the energy density of gasoline in a stoichiometric mixture with its oxidizer and not already detonated? That's where TNT beats it by a long shot. The mixture with any chance of being stored would be some relatively low pressure gas.

Edit: Or, a fair closed-system comparison to a battery would need to include a liquid oxygen tank or similar so you have the two components stored but can control the delivery...

In the context of the conversation, it doesn't actually refute the point though, which is that explosive danger is contingent on a much broader set of relations than simple energy density. Gasoline just demonstrates the disconnect. Tacking on additional conditions to make high-density batteries dangerous is exactly what the engineering goal should be.

As a stupid example, if we have a high density battery technology that never explodes unless, say, under magnetic forces only seen being produced by magnetars, that's a pretty safe battery.

Gasoline + LOX beats TNT on energy density per unit mass and per unit volume, no? There's a reason that kerosene+h2o2 is a classic rocket fuel, and TNT is not.

It's usually kerosene + O2, not H2O2. But H2 + O2 is another classic liquid rocket fuel that has higher specific energy (energy per mass), but lower energy density (energy per volume) than kerosene, and is used mostly as a 2nd stage fuel (where mass is most important). Its lower density and the need to keep it very cool mean heavier tanks, and it's also hard to work with due to being such a small molecule that likes to leak, which causes development costs to be higher.

> The previous point is fair though. What is the energy density of gasoline in a stoichiometric mixture with its oxidizer and not already detonated? That's where TNT beats it by a long shot. The mixture with any chance of being stored would be some relatively low pressure gas.

eeeh that still doesn't matter really. Gasoline is safe(r) because it needs conditions to explode (spreading into area then ignition), instead of just detonator. Diesel even more so

A damaged gasoline tank that's near empty might explode but more likely it will just leak and start burning, and probably at that moment be still extinguishable. Explosives, well, you won't have time to blink.

Batteries ? Zero chance to extinguish, gonna let it burn thru. THAT is the problem

To stoichiometrically burn 1 gram of gasoline requires 3.5 grams of oxygen, so an energy density of 9.5 MJ/g, still more than double TNT. The state of the oxygen doesn't impact its mass.

Air is usually quite available though.

Many batteries are sealed specifically for this reason.

That's a huge assumption that won't always be the case though. A gasoline tank with a small hole in it is a lot safer than a liquid-electrolyte battery with a hole in it.

Yes, that's what makes it interesting.

Interesting discussions about energetics are best had from a distance.

I can remember several situations where “a little bit of gasoline” caused a lot of problems. It’s a relative term. You need a lot of air to make it really shine, but “a little bit of gas” goes a long way lol.

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