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From: BGB <cr88192@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: C23 thoughts and opinions
Date: Tue, 4 Jun 2024 20:44:59 -0500
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On 6/4/2024 2:21 PM, Scott Lurndal wrote:
> BGB <cr88192@gmail.com> writes:
>> On 6/3/2024 3:23 PM, Tim Rentsch wrote:
>>> scott@slp53.sl.home (Scott Lurndal) writes:
>>>
>>> [ ... (internal-combustion) engines, ... ]
>>>
>>>> It's pretty clear that the ICE is becoming a dinosaur.
>>>
>>> Kind of makes it full circle, doesn't it?  ;)
>>
>> Though, annoyingly, there isn't a great alternative in some use cases:
>>    Batteries: Lower energy density and require charging (slow);
> 
> Both of which are an order of magnitude better than just a
> decade ago - and both energy density and charge time are
> a subject of intense research (both in the automotive
> and aircraft industries).  I fully expect that energy density
> per kilogram will be more than doubled in the next decade.
> 

Still pretty far tough to catch up with Ethanol or Gasoline, where it is 
also many orders of magnitude faster to refill a fuel tank than to 
charge a battery, ...

IIRC, there aren't many battery technologies that can manage a charge 
rate much over 1C to 3C (so, getting a recharge time much under ~ 20 
minutes or so is unlikely).



Vs, say, refilling something like a car in ~ 25 seconds or so at a fuel 
pump (but, could potentially be made faster if needed). Though, there 
are likely to be limits here short of redesigning the mechanical interface.

Say, it could be possible to refill a gas tank in around 3 seconds or so 
with enough pressure and active sensing, but whether this could be done 
reliably without undue risk of causing fuel tanks to rupture or similar 
is unclear (say, rather than pumping the fuel at 10 gal/min, they pump 
it at 90 gal/min, and effectively pressure-washing the inside of the 
fuel-tank).

Also would need a fairly strong fuel hose as well (likely steel 
reinforced to deal with the pressure within the hose).


The main traditional disadvantage of liquid fuel (and ICE's) vs 
batteries and electric motors, is the comparably low conversion 
efficiency. Liquid fuel would be stronger here if better conversion 
efficiencies were achieved (an ICE losing much of its potential energy 
as noise and heat).

So, ideally, need some sort of semi-efficient fuel to electricity 
conversion (possibly using a more modest size batter pack as a buffer 
stage).


Well, also some potential application areas, like human-scale robots, 
are hindered by not having any good way to power them (both ICE's and 
batteries sucking in this application area).



>>    Fuel Cells: More expensive and finicky.
> 
> And if you're going to use renewable energy to crack water
> into H2, why not just use the electricity itself (concentrate
> on better storage technology rather than H2 (gas or liquid)
> fuel cells).
> 

Yeah, H2 just kinda sucks.

Ethanol is much better as a fuel in most regards.

But, effectively running fuel cells on Ethanol (rather than H2) is a 
more complex problem. Methanol is a little easier here, but still not 
great (also methanol poses a risk due to its high toxicity).


But, yeah, not really a good way to convert electricity into Ethanol or 
similar.


Methanol could be produced using electricity assuming one can scavenge 
enough CO2 (with water as an additional input, leaving O2 as a waste 
product).


Could in theory produce methanol simply using air and electricity as 
inputs (scavenging both H2O and CO2), but the conversion efficiency 
would likely be dismal (most of the energy use would be spent running an 
air compressor, though an air-motor could recover some of this on the 
output side).

Say:
Compress air into a big tank;
Collect water that accumulates in tank;
Bubble compressed air through an amine solution (this collects CO2 into 
the solution);
Pump amine through another tank where heat is applied to extract CO2 
from the solution (it is then cooled and pumped back through the former 
tank, to collect more CO2);
Collected water is subjected to a momentary pressure drop (to remove 
dissolved CO2), and then sent in to an electrolysis stage (to get H2 
gas), with the H2 and CO2 being pumped into a heated high-pressure 
reaction chamber (to produce water and methanol, say, 250C and 75bar), 
with the resulting water and methanol being collected, then fed through 
a distillation phase (likely dropping the pressure by a controlled 
amount so that the methanol vaporizes but leaving the water behind); the 
water is then pumped back into the electrolysis step (which can also 
serves to also remove oxygen).

Likely, things like heat control/recovery would be needed to have any 
semblance of efficiency (as well, one would need to recover what energy 
they can when the waste products are returned to atmospheric pressure).


Pumping (followed by electrolysis) are likely to be the main energy 
uses, potentially much of the heating and cooling needed could be 
achieved through the compression and expansion stages (so potentially 
wouldn't need any additional energy input).

Would need to process a fairly large volume of air relative to any 
methanol produced though (so, I would expect mechanical losses in the 
compression and expansion stages would be where most of the energy loss 
would occur, such as due to friction in the pumps and similar).



....