Why don't we "just" synthesize hydrocarbons similar to what are present in gasoline/diesel/etc? We already have all the infrastructure for using, handling and distributing it.
Powerpaste, a hydrogen technology for small vehicles
61–70 of 98 posts
Re: Powerpaste, a hydrogen technology for small vehicles
#62Solving hydrogen storage has great implications. Hydrogen has high gravimetric energy density (1 kWh worth of H2 is light) but very low volumetric density (1 kWh takes up a large volume). Easy solutions are compressed hydrogen (H2 is a small molecule and easily escapes even through a material, steel embrittlement and energy for compression are big issues), cryogenic cooling (energy intensive and cryocoolers have sign…
Well, I don't think hydrogen is the answer for all these reasons. It seems, that sodium (Na) can under certain conditions (very thin film, e.g. when applied to a surface with great speed of 10s of m/s) react directly with water and produce stable electric current. That is not so hard to do, e.g. hard disks, regular turbines etc. pretty much would provide such conditions :-) The patents for such use in Lockheed-Martin…
> Sodium is very easy to handle.
It only blows up when it touches water.
Re: Powerpaste, a hydrogen technology for small vehicles
#63Used to work at the Leibniz institute in Dresden, near where this research at the Fraunhofer institute on POWERPASTE is happening. Not sure why they are trying to brand in all caps, but highly recommend adding Dresden to your bucket list post Covid. Most beautiful city I have experienced.
... and all built since 1945, an as-exact-as-possible copy of the city that had previously existed, in the same place, in 1943. It took decades of devoted work by thousands of people who loved their city, and needed to realize it again before they took their memories to the grave.
Re: Powerpaste, a hydrogen technology for small vehicles
#64Earlier quoted context omitted.
> The big question in my mind is whether direct air capture is inherently expensive Have a look at a tree... I suppose it's possible that billon years of evolution has ended on a local optimum for low energy input (direct sunlight), and we might revolutionize it with high energy (eg: high voltage electricity, fusion etc) - but I doubt it.
> low energy input (direct sunlight) Direct sunlight is actually quite powerful, around 1kW/m^2 at sea level. Although I'd guess most trees aren't particularly efficient at absorbing CO2 vs the energy they consume, which makes sense, since they only have to be as efficient as necessary to survive.
2% efficient, at best. 1000J in, 20J worth of wood and leaves out. Burning it, you get back only a fraction of that, with much of it carried away in the smoke.
Re: Powerpaste, a hydrogen technology for small vehicles
#65Earlier quoted context omitted.
Well, I don't think hydrogen is the answer for all these reasons. It seems, that sodium (Na) can under certain conditions (very thin film, e.g. when applied to a surface with great speed of 10s of m/s) react directly with water and produce stable electric current. That is not so hard to do, e.g. hard disks, regular turbines etc. pretty much would provide such conditions :-) The patents for such use in Lockheed-Martin…
> Sodium is very easy to handle. It only blows up when it touches water.
From an engineering point of view, that might still count as easy. Especially compared to hydrogen.
Re: Powerpaste, a hydrogen technology for small vehicles
#66Earlier quoted context omitted.
You don't need hydrogen, you need electrons. I prefer to store my electrons directly in atomic element 3, so I can fill it directly with electrons and get them back out, at much higher efficiencies than this process.
In all energy storage tech, you're trading off energy density (eg. energy per kilogram) against power rating (energy per second that you can transfer). Then you have trade-off considerations like safety, emissions (which have a value - see Tesla P/L), production cost, supply chain etc. For different use cases, different trade-offs may work out. Lithium battery tech typically trades off power rating and energydensity…
Ion engines are another interesting technology. They are almost the opposite of rockets: very low power and very low force, but great energy density.
Keep in mind that both rockets and ion engines actually have fairly low realized energy density, because they can't just rely on atmospheric oxygen.
Re: Powerpaste, a hydrogen technology for small vehicles
#67Earlier quoted context omitted.
> Full of combustions , not explosions. It's both, no? Aren't all chemical-based explosions considered combustion? If "explosion" means "a violent release of energy", that seems a reasonable word to describe what happens in a cylinder in about ~5 ms.
Explosion is a faster speed of burn than what an internal combustion engine is designed for.
Yes. And for another example: gunpowder is not considered an explosive.
Re: Powerpaste, a hydrogen technology for small vehicles
#68Earlier quoted context omitted.
Why not just use a closed loop hydrocarbon from electricity system as a shipping fuel if you have excess power and a need for transit? The main theoretical point of hydrogen is very high specific energy per mass but it is essentially purest acidic gas and a pain. Bonding it to something else mitigates it so why 3 H per N instead of 4 H per C? Both are toxic gases at this point leaving ammonia's main advantage in the…
The problem with every hydrocarbon-based fuel is that you need the carbon. You get that from CO2. But then you need to get the CO2. Where do you get it from? From a fossil-based plant? Well, ideally you'd want to get rid of those, not exactly smart to create incentives to keep them running. The alternative is either biomass (problematic) or direct air capture (expensive and inefficient). (Some insightful discussion o…
We need to deploy direct air capture of some form anyway because we're not reducing our carbon output quickly enough.
Re: Powerpaste, a hydrogen technology for small vehicles
#69Why don't we "just" synthesize hydrocarbons similar to what are present in gasoline/diesel/etc? We already have all the infrastructure for using, handling and distributing it.
Because the well-to-wheel efficiency of internal combustion engines isn't that good to begin with. Add lossy synthesation and it gets even worse.
If we had unlimited, clean power (hello fusion!) it might be viable.
Re: Powerpaste, a hydrogen technology for small vehicles
#70Earlier quoted context omitted.
Full of combustions , not explosions. “The speed of the reaction is what distinguishes an explosive reaction from an ordinary combustion reaction.” - Wikipedia on explosion. “An internal combustion engine nominally operates on a controlled rapid burn.” - WP on combustion.
Internal combustion engines do in fact attempt to burn fuel and oxidizer at maximum stoichiometric efficiency, and they also are trying to burn it as quickly as possible to capture all of the heat rather than exhausting a partially burnt mixture and wasting fuel. Effective explosives have the exact same chemical goals and nearly the same thermodynamic goals. If that isn’t a carefully controlled explosion I don’t know…
There are HCCI engine prototypes, but they are finicky, because the mixture (mostly regarding initial temperature and pressure) has to be in a narrow flammability band, so that it ignites precisely at Top Dead Centre from adiabatic compression heat.
If it ignites earlier, the pressures are far higher than normal. If it doesn't trigger, it won't for the complete cycle, as the piston expands and the temperature drops.
Free-piston engines have an advantage there, as they don't force the compression ratio with a crankshaft. They would decelerate the piston somewhat earlier and harder than necessary, but there are no bearings that have to handle this load.
Their issue has more to do with extracting energy from the oscillation, and keeping a stable operating point that's neither prone to stalling nor prone to runaway.