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by trollbridge7 hours ago |
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upvoteby thechao7 hours ago|
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Gasoline has 10x the energy (MJ/Kg) than TNT, but it's not a "bomb". Being a "bomb" is about energy release rate. A battery is still controlled by its chemistry.
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upvoteby vikramkr6 hours ago|
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Liquid gasoline does not have anywhere near the energy of TNT, or even a battery for that matter. It contains basically zero releasable energy. It needs oxygen or another oxidizer to react with to actually release any energy. TNT and batteries' energy density calculations include the oxidizer and the oxidizer is in close proximity to the fuel (molecularly so in the case of TNT). If you 10x the "energy content" of gasoline it's still rate limited by access to oxygen. If you 10x the energy density of a battery (the type with the oxidizer contained within the battery, not a fuel cell or metal air battery) you've got 10x the energy ready to be released quickly if oxidizer and fuel mix in unfortunate ways
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upvoteby csours6 hours ago|
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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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upvoteby saltcured5 hours ago|
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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...

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upvoteby ux2664784 hours ago|
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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.

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upvoteby SV_BubbleTime3 hours ago|
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Air is usually quite available though.
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upvoteby 3 hours ago|
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upvoteby ranger_danger6 hours ago|
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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.
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upvoteby csours5 hours ago|
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Yes, that's what makes it interesting.

Interesting discussions about energetics are best had from a distance.

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upvoteby K0balt4 hours ago|
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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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upvoteby 5 hours ago|
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upvoteby lightedman6 hours ago|
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"Liquid gasoline does not have anywhere near the energy of TNT,"

Energy density of gasoline is approximately 44 to 45 megajoules per kilogram.

Energy density of TNT is approximately 4.184 megajoules per kilogram.

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upvoteby leonidasrup3 hours ago|
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Gasoline, when in liquid form, is not mixed with oxygen and burns, releases energy slowly. In comparison with TNT which is both the fuel and oxidizing agent releases energy very fast, it has detonation velocity of 6,900 m/s.

https://en.wikipedia.org/wiki/Table_of_explosive_detonation_...

There is a way how to use the energy density of gasoline for explosive purposes, Thermobaric weapons.

"A fuel–air explosive (FAE) device consists of a container of fuel and two separate explosive charges. After the munition is dropped or fired, the first explosive charge bursts open the container at a predetermined height and disperses the fuel in a cloud that mixes with atmospheric oxygen (the size of the cloud varies with the size of the munition). The cloud of fuel flows around objects and into structures. The second charge then detonates the cloud and creates a massive blast wave."

https://en.wikipedia.org/wiki/Thermobaric_weapon

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upvoteby K0balt4 hours ago|
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A snickers bar has nearly 5× TNT’s energy per kilogram—TNT merely has the habit of being extremely impatient about releasing it.
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upvoteby 18 minutes ago|
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upvoteby moffkalast3 hours ago|
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I'm still surprised we haven't figured out a bioreactor you can feed your scrap food and turn it into energy, methane combustion notwithstanding. Like imagine feeding a roomba some sugar and it's set for a few days lol.
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upvoteby vitally36435 hours ago|
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[flagged]
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upvoteby lightedman5 hours ago|
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I read it all and even what is stated is mostly wrong UNTIL THE EXACT UNIT IS SPECIFIED.

And I'd know because I have to work with this IN ORBIT. I've had this conversation a dozen times in meetings with military and government.

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upvoteby 6 hours ago|
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upvoteby trollbridge6 hours ago|
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One of the problems with gasoline is its explosive nature, which the fuel storage and delivery system of a car attempts to mitigate. It has a better profile for burning off than a battery though since it will spill out and burn away from the vehicle.
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upvoteby not_the_fda4 hours ago|
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Gasoline isn't that explosive. You can shoot up a gas tank and it will just burn. What you see on TV is movie magic. Gasoline vapor can explode, but you need the right air to fuel ratio and a spark.
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upvoteby SV_BubbleTime3 hours ago|
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Uh… gasoline has a super high vapor pressure. If you start out at the wrong ratio, it does what it can to make that ratio right.

I’ve seen a few gasoline fires that start by burning, and then much more rapidly expressing potential.

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upvoteby capitainenemo3 hours ago|
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Requires a good mix though. The parent is still correct. Mythbusters spent a long time trying to get cars to blow up in a dramatic hollywood fashion in various episodes and determined that under most conditions it wouldn't happen.

They did get it to happen, they just had to try really hard.

In most accidents the gas tank will not blow up.

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upvoteby vablings2 hours ago|
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High velocity accidents where the gas is quickly dispersed into the air is pretty much the only way that happens.
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upvoteby leonidasrup3 hours ago|
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"Fast X: why cars don’t really explode when they crash"

"Petrol and diesel can only explode when under pressure and mixed with air and in the case of petrol, have a small amount of energy added in the form of a spark or a flame. Engines pressurise the fuel/air mixture in the cylinder and so produce small, confined explosions which turn a crankshaft and drive the wheels."

"When cars are involved in collisions, fuel lines are often torn and petrol leaks out onto a hot engine. Liquid petrol can catch fire in the presence of air. But it can’t explode because it’s not under pressure and is in the liquid phase rather than a vapour."

https://theconversation.com/fast-x-why-cars-dont-really-expl...

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upvoteby jimt12343 hours ago|
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> Gasoline ... it's not a "bomb"

My teen years would beg to differ, when some neighborhood friends and I decided to experiment with gas and bleach. The neighborhood residents, fire department and local police also had an opinion, too. (We all got into BIG trouble. Definitely one of the dumber things I did as a teen.)

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upvoteby duped6 hours ago|
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Poorly stored gasoline can spontaneously combust, though. So more like a firebomb.
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upvoteby not_the_fda4 hours ago|
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No it can't. To combust it needs ~ 500F. If you left it out uncovered in the open and allowed the it to vaporize with a spark nearby, it might explode, but thats not spontaneous combustion. Gasoline sitting in a sealed container wont spontaneously combust.
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upvoteby swiftcoder4 hours ago|
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Didn't everyone have one of those old mechanic friends who liked to put the cigarette out in the can of gas to scare the tourists?
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upvoteby SV_BubbleTime3 hours ago|
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That is definitely one of those “it worked the first 50 times no problem” tricks.
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upvoteby ridgeguy4 hours ago|
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Gasoline doesn't do that. Perhaps you're thinking of the following?

What it does do is slowly polymerize, becoming useless as an ICE fuel in time, typically in a year or two. This is why backup generators should run on propane, which has no degradation mechanism.

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upvoteby duped3 hours ago|
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No, I'm thinking of improperly stored gasoline evaporating and combusting.
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upvoteby emptyfile6 hours ago|
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upvoteby interstice6 hours ago|
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Some heavier elements have hilariously high energy densities and aren't bombs (on their own), but the catch is the energy release is a trickle. Point is it's not an automatic follow that high density = high discharge.
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upvoteby butvacuum6 hours ago|
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Have a look at Electric impedance spectroscopy- https://en.wikipedia.org/wiki/Dielectric_spectroscopy

Theres a handfull of Tier 1 BMS chips that support it already. though, half of them are meant for traction/EV packs instead of BESS.

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upvoteby HPsquared3 hours ago|
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Making it require air (or some other kinetic / transport process) would help with that. E.g. zinc-air battery.
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