Re: C23 thoughts and opinions

On 6/4/2024 10:59 PM, Paul wrote:

On 6/4/2024 9:44 PM, BGB wrote:

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).

 There are whizzy solutions. But they're not practical for consumer automotive.
 

As can be noted, I was also partly trying to come up with something workable in the 500W to 2kW range; where neither ICE's nor batteries are a good solution.
Examples of things one might find in this power-range:
   Lawn mowers;
   Chainsaws;
   ...
Or, futuristic applications, like human-sized quadruped or biped robots.
Here, both batteries and ICE's suck.
Batteries work well for a cordless power drill (typically 100W to 250W). For a chainsaw or lawnmower (1kW to 2kW), not so much.
ICE's work reasonably well for a car (say, around 50kW to 200kW), but for a chainsaw, they are very noisy and blow smoke in the user's face (so, poor user experience). And, no one is going to want a running chainsaw engine in their house, ...
As noted, some other technologies exist, but are not used much in this space:
Turbines, but these have generally not been particularly efficient at smaller sizes.
Rankine engines have also not seen much use; these traditionally work by boiling a working fluid and using the vapor to perform work (spinning a turbine or driving a turbine). In their most well known application (steam powered locomotives) the working fluid was water being heated by coal.
If using ethanol, the ethanol could be used as both fuel and working fluid (if it is already boiled into vapor, something like a propane burner nozzle could be used to good effect).
Ethanol has a lower boiling point than water (and is highly flammable in vapor form), which could be useful in this application; and has a moderately low toxicity (in its pure form) so would be safe to handle (though, when sold as fuel, it is often adulterated in ways that increase its toxicity).
Pretty much no one has done this that I am aware of. But, getting such an engine started up would be annoying (would need some alternate mechanism to heat the boiler to get the engine started). Likely also (if using pistons) it would need at least two or three pistons to allow for cold start (if one had 3 pistons 120 degrees out of phase, then at least one of the pistons will be in a position to start the engine spinning once pressure starts to build).
The pistons would effectively operate with only two cycles (intake and exhaust), effectively operating like a reciprocating pneumatic motor. The design would also need to minimize heat loss in the cylinders, since if the cylinders loose too much heat, the working fluid could start to re-condense in the cylinders.
Possible options:
More complicated: Making the block and pistons out of polycarbonate and similar, with PTFE piston rings;
Simpler: Making block and pistons out of aluminum, but then encasing the block inside of acrylic or rubber to reduce thermal losses (due to the high thermal conductivity of aluminum). Though, there would still be potential heat loss via conduction via the crankshaft, ...
While vane-motors also exist (and are common in pneumatic power tools), they have a drawback (shared with turbines) in that their efficiency sucks.
But, yeah, can still note that no one has seemingly used a Rankine cycle engine for powering something like a chainsaw or lawnmower (or a robot...).

The battery chemistries have "spider diagrams" which evaluate the battery on
a number of factors. And that is how we've settled on what is inside cars today.
The lifetime of the battery pack, received a high priority. A ballpark number
is 5000 charging cycles. Real cars, some of them it might be closer to 1800.
And leaving a car sitting in the hot sun, might contribute to some of the
difference there. The charging history is part of it, but exposing the automobile
to harsh conditions, can also impact the battery a bit.
 The solid state batteries in the lab, are around 1000 charge cycles currently.
These have no liquid electrolyte like the currently-shipped batteries.
 There have been announcements of lab demos of battery chemistries
with extremely short charge time. But then, the number of charge cycles is
a joke.
 There was even a vehicle that went 1000 miles on a battery. Why ? Because
the battery was not rechargeable at all. The battery, at destination,
needed to be sent to a recycler. But that particular experiment was intended
to prove they could build a battery trip with more range than your bladder.
 

I had heard about zinc-air, aluminum-air, and alkaline batteries being used in this context. Seems like a no-go.
Of the commonly used batteries, seemingly the most suitable to fast charging are NiCd and NiMH chemistries, but the energy density for these is worse than for Li-ion or Na-ion chemistries.

These are all examples of spider diagrams, where multiple points on the
diagram are a compromise. And if they don't compare favorably to a 5000 charge
cycle battery, you won't see them in a car. Not with an 8-year warranty.
     Paul