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Audi e-diesel takes a bad idea and makes it worse
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Raffy.Roma
Rome (Italy)
IMO Audi's lack of engineering is the evidence that in Europe we are far away from understanding how to handle the CO2 reduction of emission.
all process are carbon neutral unless you are talking about fusion, fission or getting off the planet.
I think the concern here is atmospheric carbon. in that case if you are using a non-gas source of CO2 this may not be carbon neutral at all.
Anyways this seems like an old process that was used in WWII for synthetic jet fuel.
Probably just more of the Audi Hype Machine
I think the concern here is atmospheric carbon. in that case if you are using a non-gas source of CO2 this may not be carbon neutral at all.
Anyways this seems like an old process that was used in WWII for synthetic jet fuel.
Probably just more of the Audi Hype Machine
jgs
Active Member
Of course not, but the same can be said of absolutely anything, including batteries. The energy inputs can be carbon-neutral, is the point, and if they are then the cycle is carbon-neutral. (Actually it might be slightly better than neutral, because probably not every single gram of fuel gets burned, so some minuscule part of the carbon captured during fuel production remains captured instead of returning to the atmosphere.)
Me too >_<
I started reading other articles about other synthetic fuels and when I was deep in the rabbit hole I emerged unfairly ascribing some characteristics of other systems to Audi's.
Audi's seems just a chemical energy storage scheme. Very inefficient generation-to-wheel but not necessarily open loop.
If you have a hydrocarbon (CnHn) and you get complete combustion, you add oxygen, break up the C-H and C-C bonds and you end up with CO2 and H2O.
Since the inputs to produce the hydrocarbons are H2O and CO2, you should end up with the same amounts of CO2 and H2O at the end.
So, it's theoretically closed cycle, and results in moving H2O, CO2 and O2 to different places. Reality would be leakage and incomplete combustion, of course, but the process is not specifically "trapping" the water in other chemicals.
jgs
Active Member
Your use of "sequestration" is a bit confusing to me -- normally I associate that with deliberately removing carbon from the atmosphere, typically as an offset to some other CO2-releasing process, e.g. so-called "clean" coal. In the Audi process, I wouldn't call what they're doing "sequestering" the CO2 since the intent is to release it again. But if you didn't burn the fuel I guess it would be sequestration.
Indeed. It's not clear if you're disputing this, but the process Audi describes is indeed carbon neutral
[*], because it uses the atmosphere as both source and sink for CO2, and sinks no more than it sources. The article linked from the OP isn't clear that the CO2 source is the atmosphere, but this article is clear on that point: Audi is creating synthetic diesel from air, water and green energy
A bit of a tangent, but the NRL process I linked to earlier uses seawater as the CO2 source, if I recall correctly. Which works out to much the same thing, in terms of carbon reservoirs. In either process, the point is that CO2 is a feedstock at the front end as well as effluent on the back end, and in equal quantities.
[*] Assuming the energy input is carbon neutral, such as the windmills in Audi's pretty graphic.
ThosEM
Space Weatherman
Carbon neutrality and other emissions are only half of the story. There is also energy efficiency, which if bad enough, will eliminate the cleanliness advantage. Even if such a clean (or neutral) burning fuel is real, it would make more sense to burn it in a power plant turbine to make electricity for EVs, than to burn it in an inefficient Carnot cycle engine.
So I don't agree, EV are great for passenger cars, but what about trucks (18 wheeler) or Trains. We still have to move goods around the world. A clean diesel is the only this can happen. Airplanes will never be electric....
So while Audi developed this for a SUV, the implications are much larger. and in a good way.... lets not knock alternatives to big oil....
So while Audi developed this for a SUV, the implications are much larger. and in a good way.... lets not knock alternatives to big oil....
Elon is talking about how batteries might get to 400 Wh/kg in the next decade, but gasoline/avgas is like 13000 Wh/kg.
A 757 on a cross country flight might carry 30 tons of fuel. The equivalent energy in batteries would be like 1000 tons of batteries.
A 757 can carry about 60 tons worth of fuel and people. How could it possibly carry 1000 tons of batteries?
Sure, you say, an electric motor is more efficient than a gasoline engine, so you need less energy, so maybe only 250 tons of batteries could carry the plane and the people. but it doesn't work like that because a plane has to do a lot of extra work to keep all the extra battery weight in the air, so the electric plane might actually need more energy just to lift its own batteries.
To me, it seems like batteries need to improve by more than an order of magnitude in energy density for them to be commercially viable as the main energy storage on an airplane. I don't see that happening for some time.
What does Elon see that I'm missing? Usually Elon seems quite practical.
jgs
Active Member
The other thing is that even if you imagine you get the energy density you need for commercial aviation, there's still the military. They require very energetic fuel sources for many of their applications. The U.S. military is said to be the single largest consumer of oil in the world, so even if only the military niche requires liquid hydrocarbon fuels, that's still a big deal.
I realize this isn't what you meant, but some of them already are:
NASA Helios - Wikipedia, the free encyclopedia
If we get lighter, more efficient solar panels, some sort of hybridization may make sense for airliners in longer cruises (right now the added weight requires more fuel than the energy could save,) and I know companies are working on electric drive for taxiing on the ground.
I'm not convinced everything will go that way, and it's still a very long way to go, but it could happen. You're certainly right that airplanes are the application that's hardest to make fully electric, and likely one of the last things that will continue to burn long chain hydrocarbons. For shorter heavily traveled routes, they might be replaced by high speed electric trains (elevated or encapsulated.)
As for the rest of it... You can build a pretty convincing semi tractor using 5 Model S battery packs and two of the original big rear motors (with an additional ~3:1 reduction.) It won't be much heavier than a current Semi, and will get 250-300 miles fully loaded. (But you'd need half a megawatt or so to Supercharge it...)
Trains are better done as electric by overhead catenary line anyway - almost all european trains are that way, along with much of the east coast and much of asia. My hope would be to replace most of the long haul coast to coast type trucking with electric trains.
Walter
stopcrazypp
Well-Known Member
I think for long haul 18 wheelers, CNG/LNG is the only viable alternative right now. An all-electric solution would be trains and short haul trucks. However, the technology isn't so far off that an all-electric 18 wheeler isn't possible.
I remember Elon saying around 500Wh/kg is when it begins making sense to consider an electric jet. And I believe his goal was something like the Concorde, which carried 95 tons of fuel. And the rest I think would have to be achieved by efficiency optimizations you can do from not having an air breathing engine and not having energy storage that can slosh around and can change weight as it depletes (this was an issue in the Concorde).
However, I think lithum air (which can practically achieve 2000Wh/kg, theoretical is 11kWh/kg, 5000Wh/kg including oxygen) is probably the chemistry that can make electric commercial aircraft possible, although you lose the advantages mentioned above (since lithium air batteries need air and get heavier as they deplete). Lithium sulfur theoretical is about 3000Wh/kg, achieved is 500Wh/kg, I don't have a source, but I'm guessing practical achieveable would be ~1000Wh/kg (20-30% of theoretical is typically achievable).
Keep in mind you can't use the fuel density as a straight comparison. Even though a jet turbine is efficient, it's still not as efficient as an electric motor since a lot of the energy in the fuel is lost as heat (wiki says cycle efficiency for a jet turbine is still only around 30%). That would bring the jet equivalent to ~4000Wh/kg.
I remember Elon saying around 500Wh/kg is when it begins making sense to consider an electric jet. And I believe his goal was something like the Concorde, which carried 95 tons of fuel. And the rest I think would have to be achieved by efficiency optimizations you can do from not having an air breathing engine and not having energy storage that can slosh around and can change weight as it depletes (this was an issue in the Concorde).
However, I think lithum air (which can practically achieve 2000Wh/kg, theoretical is 11kWh/kg, 5000Wh/kg including oxygen) is probably the chemistry that can make electric commercial aircraft possible, although you lose the advantages mentioned above (since lithium air batteries need air and get heavier as they deplete). Lithium sulfur theoretical is about 3000Wh/kg, achieved is 500Wh/kg, I don't have a source, but I'm guessing practical achieveable would be ~1000Wh/kg (20-30% of theoretical is typically achievable).
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Well I did mention the efficiency difference in my post. but with it, I pointed out that you need more energy to lift a plane with 100 tons of batteries in it. Unlike a constant speed car on a freeway, a plane's energy usage depends heavily [sorry] on its weight.
To carry 1000 kg more weight, you need somewhere around 600 kWh of useful energy. With gasoline, that means you add 150 kg of avgas = 2000 kWh of chemical energy = 650 kWh of useful energy, and off you go. With batteries, 400 Wh/kg means that the battery doesn't have enough energy to carry itself across the country, nevermind carry itself and cargo. Lastly, with gasoline, you dump it into the atmosphere as you go, so by the end of your journey you need less fuel per mile than at the start. Batteries aren't going to work that way.
stopcrazypp
Well-Known Member
As with cars, where there is a limitation, simply make a plane with less range. It doesn't necessarily have to start out as a transatlantic, transpacific or cross-country plane, but can be a regional jet first and work from there.
Bulletproof
Former Vendor
I think what Audi is trying to do is not so much revolutionize the world, but to show that it is a relevant company. If you take its past four decades, it tried to beat BMW and finally got caught up with it, some might even say surpassing BMW. Unfortunately, by that time, the tide turns away from diesel to electricity, leaving the company with a lot of somewhat wasted research money. Then we witnessed the sad back and forth on the e-tron, and only after an officer reshuffle, it decides to use the well spent R&D on electricity for a PHEV and an eventual, far away real EV. It also knows that Toyota is the top eyeball dog in this game, thanks to a well funded PR department, and despite countless recalls, is still perceived as competition. Will Audi ever do anything with its "breakthrough"? Most likely never. But it sure is great publicity. At the very least, we're talking about it 
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