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Discussion Starter #61
Coward, you only deem other alternatives as wasteful, because you don't want the feasibility of your preferred solutions to see the light of day. For policy makers to make decisions, they must see the various technologies market tested, which is what is happening today. Since a 100% BEV costs $100K, it is clear that EV's are nowhere near ready for broad acceptance in our economy, while less attractive solutions like ethanol from corn and hydrogen from natural gas is.

I do have my favorites, but having succeeded in high tech by iterating a tech through less preferred incarnations, until you reach the ultimate solution, I KNOW how to best drive a broadly accepted answer to existing problems - YOU do NOT.
 

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Hey Lyle, What's the banning policy here? Jason has clearly lost his grip with reality. I'm sure the real juicy expletives are on their way. I can hardly wait. I have already decided to not debate with him any longer but I'm guessing he would like to continue insulting me from behind his computer screen. Anyway, I have already hit the virtual ignore button. I'm also hoping his mother takes away his computer privileges. ;)
 

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I always thought that cowards were people that insulted others on the Internet because they didn't have to worry about the consequences. I can guarantee that you wouldn't be insulting me if we were standing in front of each other. When you write something pretend you are in the same room as the other person. I played sports my whole life and always enjoyed healthy banter. However, there is a point when it's no longer healthy and it becomes down right insulting. When that happens I guess you can imagine what happens. You do understand the dynamics right?
 

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Discussion Starter #65
I have my full name listed at the top of every post, how 'bout you? Further, your insistence on trying yet another intimidation tactic just reinforces that you are a bully, and used to brow beating people into compliance. Not getting any traction with me though, huh? Must be pretty frustrating for someone like you who's used to getting your way by force.

I'll let you in on a little secret - those who tried those tactics with me in person no longer get in my face, as they aren't prepared to go as far as I'm willing. Like you, they run for the school teacher.

Any and all these techs are going to be necessary to quickly move our economy from one with a severe energy trade deficit to a trade balance. Those who interfere are only trying to line their own pockets, while wrapping themselves in a thin veneer of sophistication and altruism, which you reveal yourself to be more and more each day.
 

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How far ARE you willing to go? I'm guessing "those" who tried to get into your face but who no longer do (notice a pattern?) head for the hills because they probably realized you are slightly off kilter, ever think of that? Funny, I also have this feeling. Something like, "Oh no, he's a stalker." If I ask you real nice will you just go away? Seriously dude, take your medication!
 

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boys, may I step in?

If Texas and Jason can stop squabbling for a minute, I would like to insert some technical data.

Some good news and some bad news about compressed air energy storage.

First, the good.

If energy is cheap, compressed air beats out current generation LI batteries hands down for energy density per unit weight. See http://en.wikipedia.org/wiki/Energy_density

Note that compressed air has an energy density of 0.512 MJ/kg by weight at about 0.14 MJ/liter at 300 bar (4500 psi). Compare to LI's current density of about 0.25 MJ/kg. I think the volumetric energy density is about 0.3 MJ/L.

If you can compress the air to 600 bar (9000 psi), you about double the energy density again in both weight and volume. That's 4 times the energy density per unit weight of LI and about equal the volumetric density.

Now the bad news -
There are two problems. The first is efficient compression. Thermodynamic limitations start to kick in. About all that a state-of-the-art 4-stage inter-cooled compressor can do is 85%. This is very sophisticated industrial technology, usually reserved for compressors rated at 100's of HP.

So you might think, why can't a compressed air station just have a big tank and compressor (like they do for filling tires) and air engine owners just pull up, scan their credit card, and fill up?

Answer - filling a low pressure tank from a high pressure tank is very inefficient, energy-wise. Ultimately, my figures show that it could waste up to 50% of the energy. For those with thermodynamics training, this would be an isenthalpic, irreversible pressure reduction. This was actually a test question one of my thermo classes from long ago, so I remember it well.

Here is the way to think about it.

You put in X amount of work to compress Y lbs of air to 10000 psi in a tank. You connect that tank to a second tank that is at 0 psi. You open the valve. Air flows through the valve from one tank to the other tank until both are at 5000 psi. Let them set and assume ambient temperature again. Now you want to re-empty one tank and put the air back in the other tank at 10,000 psi again, just like you started. You will have to put in about X/2 more work to get the system back in its original state. During the filling process, you lost X/2 energy to entropy increases.

This will happen anytime you fill an empty tank from a high pressure tank through a valve. There are two ways to avoid this entropy loss. The first, and simplest, is to fill the empty tank directly with the compressor.

To fill up one 16 kW-hr air tank in 6 minutes (0.1 hours). (16/0.1)/0.85 = 188 kilowatt-motor to fill up your tank. The equivalent of your local Shell station would have to have several hundred kW of compressors to serve multiple vehicles. This gets to be pretty outrageous.

The second is to have an air turbine in the filling stream that "expands" the air to the lower pressure of the empty tank, recovering a portion of the lost work from the expansion and generating some electricity. I'm not sure how much recovery you could get, but let's just say for calculation's sake that it were 50% of available. That would reduce the entropy losses to 25%. This means the net W2W efficiency would be 0.75 x 0.85 = 63%. A lot better than hydrogen's W2W, but not as good as current technology LI batteries.

One key advantage of BEV's is that they can plug into the electric grid pretty much everywhere and re-charge, with minimal hassle and waste. The battery's high-tech, but the charging technology is mainstream.
To re-charge an air car by plugging into an outlet, you'd need a little 1 HP 10,000 psi onboard compressor (with the 4-stage intercooling).

That will take some mechanical breakthroughs that make future LI battery nanowire concepts look simple by comparison.

The second problem is trying to get more energy density out of compressed air than already available. It basically means even higher pressures. We'd have to go to 20,000 psi to get another density doubling. The storage tanks, compressors, etc. start to get pretty hairy at that pressure. the case of diminishing returns kicks in.

Compressed air does have some long-term potential in the wind-energy market, where 5 MW wind turbines could direct-drive the compressors, store the air in deep underground reservoir, and realize a bunch of efficiency improvements.

In conclusion, Jason's right about this being a pretty interesting idea, but it would be a short-term solution while power is still cheap and LI batteries are still improving. When electricity gets more pricey, W2W efficiency issues will dominate and and electro-chemical energy storage solutions will probably win-out.
 

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Discussion Starter #68
hvacman,

Yes, I agree. I believe that compressed air tech will gain a temporary foothold in our vehicle markets, which will put more price pressure on battery tech. Simple emissions standards won't force people to batteries, if batteries are still expensive, so they will turn to simpler things like hydraulics and pnuematics.
 

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Hey hvacman, nice analysis. Ah, the beautiful numbers. You sound like a man of reason. Let me ask you this... Say you have two 16 kWh drive train systems with similar final horsepower ratings (say 75 hp). These systems are installed in two cars using the same aerodynamic body and tires:

System 1 - Air Car technology (2010 expected technology):

This drive train system has the latest 10,000 psi carbon fiber tank technology, multistage intercooled air motor (need both the multistage and intercooling to get anywhere near isothermal expansion), mechanical transmission to drive wheels. It has all the electronics including digital pressure and flow control as well as all the associated high pressure lines, pumps, valves, safety systems etc.

System 2 - Battery technology (2010 expected technology):

This drive train system has the latest, safe lithium-ion battery technology (A123 or similar) contained in it's customized battery pack. It's connected to a high efficiency controller and AC drive motor. It has all the necessary connections including plug-in port, battery environmental controls, wiring, safety systems, etc.


Results Predictions:

1) Which system would have the higher volumetric energy density (remember that the entire storage system must be considered. Since giving the gas a high potential energy requires it to be constrained at extremely high pressures I feel this is a important consideration. The main tank used for the Ford hydrogen concept car has only a 5,000 psi tank but the walls are 2 inches thick of kevlar and carbon fiber (this is the only thickness data I could find). If we were to include the entire system (motor, storage, electronics, transmission, etc.) How would that change?

2) Which system would be cheaper to produce in large volumes?

3) What would be the final real-world plug-to-wheel efficiency of each system? How would this effect the operating costs of the system?

4) How far would each system go starting with a full charge(regeneration braking not considered, although essentially free for the electric system)?

5) Which system would have lower maintenance costs? Remember that current high pressure vessels transported on US streets have a life of 15 years and must be water tested every 5 years (not sure what the new regulations would be but there will be regulations).


Anyway, curious as to what you feel are the answers to these questions.
 

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shades of engineering school!

Good question(s). Sound's like something from my PE exam way back when. You aren't with the board of registration, doing a surprise re-check on my license, are you?

How about if some other engineering-type steps up to the numbers plate and takes a swing? My office manager keeps mumbling something in my ears about "billable hours". Until I can figure out how to charge GM for this analysis, it'll have to wait a bit.

Keith
 

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shades of engineering school!

Good question(s). Sound's like something from my PE exam way back when. You aren't with the board of registration, doing a surprise re-check on my license, are you?

How about if some other engineering-type steps up to the numbers plate and takes a swing? My office manager keeps mumbling something in my ears about "billable hours". Until I can figure out how to charge GM for this analysis, it'll have to wait a bit.

Keith
 

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oops - double clicked on the reply.

Haven't run any numbers yet, but here is a link to an interesting paper that reviewed the well-to-wheels efficiency of hydrogen, LI batteries, and air. I haven't studied it much, but it may have a good start to many of the answers.

http://www.efcf.com/reports/E18.pdf

You might note that intercooling is required during compression. The air motor requires heating between stages to be isothermal.
 

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Haven't run any numbers yet, but here is a link to an interesting paper that reviewed the well-to-wheels efficiency of hydrogen, LI batteries, and air. I haven't studied it much, but it may have a good start to many of the answers.

http://www.efcf.com/reports/E18.pdf

You might note that intercooling is required during compression. The air motor requires heating between stages to be isothermal.

Oh, my bad. I thought the multistage motor heat exchangers were still called intercoolers because they are so similar physically. What are they called? interheaters? lol. Anyway, here's what Ulf's report states:

"As expected, the highest efficiency is obtained when the expansion process proceeds close to the isothermal limit. From an energetic standpoint, the best results may be obtained by using a multistage expansion motor with heating between stages.

-Figure 7 T-s-diagram of a four-stage expansion compared to a single-stage expansion (point 4) -

The thermodynamics of a four-stage expansion with three heat exchangers has been analyzed. As the cold exhaust is released into the atmosphere, nature will take care of the final heat exchange to restore the original ambient conditions. It's assumed that all heat exchangers are sized to raise the temperature of the air exhaust of all but the last stage to 20°C. This is not easily accomplished on hot
summer days, but may be possible under cold weather conditions."


hvacman, sorry about the questions. Others can feel free to add their analysis. My intentions are actually to explore the viability of an air car for the application I originally suggested - car for a crowded city like those found in India. Reading the report that you linked to I noticed the following:

"However, because of the different densities hydrogen
compression requires 15 times more energy than air compression for identical initial volumes and identical pressure limits."

Is this correct? Anyone? It seems like a mistake. Anyway if true the hydrogen car is even worst off than I thought before. I would like to see a real-world test of this. If true, that would make the hydrogen car highly impractical (as the author states). I need confirmation! lol. Anyway, back on topic. The author then states:

"Compressed air vehicles, if engineering hurdles can be overcome, promise an efficiency equal to that of FCVs. However, the lower energy density of compressed air will limit the maximum range of such cars to values appropriate only for in-city commuting. "

That agrees with my previous post results. Compressed air has very low amounts of stored energy per volume when compared to other technologies. If I would have included all these inefficiencies in my analysis (I didn't need to in order to prove the point) it would make the number of Quantum units go up by quite a bit.

If the author is also correct in stating that his example car would go 133 km on lithium-ion but only 46 km on compressed air then the example I used in a previous post would make the 16 kWh air car highly impractical, even for city driving. The lithium-ion to compressed air drive distance ratio would be an amazing 2.9 to 1 Let me use my previous Volt example:


Volt:

16 kWh battery pack - distance traveled: Approximately 50 miles (assume the set points can be opened up slightly for BEV operation).



Air Car:

16 kWh Battery pack - distance traveled: 50 / 2.9 = 17.3 miles!


Wow, that figure along with honest answers to my previous questions would just about guarantee that we will never see a practical Air Car. I think the author may have exaggerated a bit. It just couldn't be that bad for the Air Car. Could it? I will need to see the actual data from the Tata Air Car, if it ever makes it to production, to see for myself. Anyone still feel the Air Car has a chance? Things are looking very grim.
 

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Discussion Starter #74
Once again, you fail to compare the cost of a 16 kWhr battery / motor vehicle with a compressed air tank and air motor.

Below is a link to an article that shows how hydraulic systems (similar to air / pnuematic systems) are already deployed with FedEx with Eaton providing a hydraulic system for garbage trucks which is completely free of electric motors and batteries:

Link to article

As EV's come at a steep premium, we will see the proliferation of mechanical energy storage systems in heavy vehicles with lots of stop and go driving requirements.
 

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Once again, you fail to compare the cost of a 16 kWhr battery / motor vehicle with a compressed air tank and air motor.

Below is a link to an article that shows how hydraulic systems (similar to air / pneumatic systems) are already deployed with FedEx with Eaton providing a hydraulic system for garbage trucks which is completely free of electric motors and batteries:

Link to article

As EV's come at a steep premium, we will see the proliferation of mechanical energy storage systems in heavy vehicles with lots of stop and go driving requirements.
Oh did I? Here's what I wrote a few posts back. Look at my questions 2 and 3:


"Let me ask you this... Say you have two 16 kWh drive train systems with similar final horsepower ratings (say 75 hp). These systems are installed in two cars using the same aerodynamic body and tires:

System 1 - Air Car technology (2010 expected technology):

This drive train system has the latest 10,000 psi carbon fiber tank technology, multistage intercooled air motor (need both the multistage and intercooling to get anywhere near isothermal expansion), mechanical transmission to drive wheels. It has all the electronics including digital pressure and flow control as well as all the associated high pressure lines, pumps, valves, safety systems etc.

System 2 - Battery technology (2010 expected technology):

This drive train system has the latest, safe lithium-ion battery technology (A123 or similar) contained in it's customized battery pack. It's connected to a high efficiency controller and AC drive motor. It has all the necessary connections including plug-in port, battery environmental controls, wiring, safety systems, etc.


Results Predictions:

1) Which system would have the higher volumetric energy density (remember that the entire storage system must be considered. Since giving the gas a high potential energy requires it to be constrained at extremely high pressures I feel this is a important consideration. The main tank used for the Ford hydrogen concept car has only a 5,000 psi tank but the walls are 2 inches thick of kevlar and carbon fiber (this is the only thickness data I could find). If we were to include the entire system (motor, storage, electronics, transmission, etc.) How would that change?

2) Which system would be cheaper to produce in large volumes?

3) What would be the final real-world plug-to-wheel efficiency of each system? How would this effect the operating costs of the system?

4) How far would each system go starting with a full charge(regeneration braking not considered, although essentially free for the electric system)?

5) Which system would have lower maintenance costs? Remember that current high pressure vessels transported on US streets have a life of 15 years and must be water tested every 5 years (not sure what the new regulations would be but there will be regulations).


Anyway, curious as to what you feel are the answers to these questions."


Well, I asked the question but did not get a response. What are your estimations of the cost of a 155 liter 10,000 psi carbon fiber tank (thickness more than 2 inches thick) with associated multi stage and multi interheated (still not sure of the name for this) air motor with associated control electronics and high pressure devices? When you are done with that tell me if that's worth the 17.3 miles you will get from that.

I'm ready to go to the minute details on this. Let's get going! From the required tank size, to operating cost. Just throw out some numbers for me. Propose the air car or range extender that you mentioned in earlier posts and let's get to work.

Oh, an now you are tying to slide yourself into an almost insignificant hydraulic / pneumatic device as a way of vindicating your original position? Do you realize that the link posted before is for a non electrical system that can store the braking energy and allow that energy to help get the vehicle moving again? A sort of a non-electrical regen system. Do you know how much energy that is? Well, get in a truck and step on the brakes. How far did you go? You will get about 75% (that is what an electrical regen system gets) of that energy back. Is that a long distance? Did I ever say that was impossible? Does that violate the laws of physics or have an unrealistic system volume? No, no, no, no and no. Shame on you.


Here, I will state it clearly:

1) A BEV will be cheaper to purchase and operate than a vehicle using air car technology. From golf cart to Tesla class. You don't think so? How about you propose a practical air car vehicle and let's work on the costs.

2) If you then propose to include a liquid fuel air heating system to the air car to increase the volume of the compressed air in order to extend range (what seems like the next plan for air car developers) then I claim it will be far cheaper to purchase and operate a vehicle that uses a turbo ICE. It will emit less CO2 as well!


Summary:

If you want an inexpensive-to-purchase and operate environmentally friendly short-range vehicle that uses no petroleum fuel buy a small BEV city car. Think Tata with a small motor and battery.

If you want an inexpensive to purchase and operate vehicle that has more range but uses some petroleum fuel buy a small turbo ICE car. Think Tata with a tiny and efficient VW turbo diesel. Do you think you will be able to heat the compressed air for the air motor using a petroleum fueled air heater better and more efficiently than the highly developed VW turbo diesel (both are mechanical devices that use compressed air and liquid petroleum fuels to expand gases to push pistons). Fat chance. You'll get more efficient use of fuel inside the cylinder of that diesel than you will outside of the cylinder with the proposed air heater.
 

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Discussion Starter #77
Texas,

You can set up your strawmen as much as you want, fudging numbers to achieve your outcome - I wouldn't expect anything better of you.

As I posted above, mechanical energy systems are finding their way into Formula One and FedEx delivery fleets, and compressed air will find its place(s) as well. All these things are going to have applications where heavy and expensive battery packs just won't be feasible.

You can go hang out with all the other sideliners, who are missing out on the real innovations in this industry - people so steeped in their text books, that they can't contribute to future advancements. You will forever be a spectator of advancements, cheering only for what is provided to you, not made by you.
 

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Eaton hydraulics

Link to Eaton's hydraulic series hybrid

As a new member to this formum, I don't know which one of you started this food-fight, but knock it off. If you'd both get off the name-calling kick, you'd see that both of you post the most interesting and informative messages on the forum.

Jason, Texas' numbers look ball-park right - the odds aren't good that a straight compressed-air energy system as proposed by the Air Car will actually ever pencil out economically.

Texas, I know you may hate to hear it, but Jason's on to something here with this hydraulic concept. Very interesting.

It looks like Eaton's system actually stores energy in two closed hydraulic fluid/air compression tanks (called accumulators). As the hydraulic pump/motor increases system pressure, fluid enters the high pressure tank and compresses the air.

It taps energy by drawing hydraulic oil off the hi pressure tank, allowing the air to expand and reduce pressure. Because the tanks will be steel, have a large surface area, and are exposed to ambient air, there is adequate heat transfer to make both the air compression and expansion cycles work isothermally without all the intercooling/heating.

This is a very creative way to simplify the entire compressed air energy-storage thermodyamic cycle using off-the-shelf components and great idea for commercial vehicles. Liquids are a lot easier/more efficient to mechanically pump than gasses are to mechanically compress.

On the negative side, the energy density per unit volume will be very low, as there has to be two tanks, not one (it is a closed system), and the pressures have to work with standard hydraulic pressures in the 2000 psi range. This would limit its all-hydraulic range probably to dynamic braking energy recovery and some engine power boosting.

I'll have to see if I can dig up the operating efficiencies of hydraulic pumps and motors so we can get a W2W efficiency calc.

Keith
 

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Discussion Starter #80
hvacman,

It appears that Engineair has some competition:

APT Air Engine

20krpm Wolfhart Air Motor

Air cars will still find their niche. I think they would be most feasible as range extenders for PHEV's in cities demanding zero emissions vehicles.

Hydraulics find their greatest feasibility in very heavy vehicles where the equivalent battery tech would weigh tons and costs tens of thousands alone. You are correct that they will only be used as a regenerative braking / launch assist system.
 
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