Thanks for the wisdom, oh Obi Wan...
Obi Wan Spiccoli
cheers
Compressed Air Car
To return to jollyrgr's original question:
The 46 MJ figure quoted as the stored energy in the tanks is probably a little optimistic, but in the right range.
Consider a cylinder 1 sq ft in cross section and 3750 feet long. For isothermal compression, the volume times the pressure is constant. If you move the piston in a short distance, the air pressure rises as the volume reduces. The work done can be approximated by using the average of the starting and ending air presssures times the distance the piston is moved. This can easily be done for 100 points using a spreadsheet such as Excel. There will be some error in the results, but probably only a few percent.
For a compression ratio of 300, I get that the total work required would be 31 million ft-lb, 11.75 KW-Hr, or 42 MJ.
During compression, heat must be romoved from the air to keep it at the same temperature. When the air is expanded, this heat will have to be replaced or there will be some loss in efficiency.
The usable energy in the air tank may be a little less, since the motor may not be usable when the pressure drops below a few hundred psi. This will reduce the range but will not necessarily reduce the overall efficiency.
If the charging efficiency was 80 percent (90 percent electric motor, 90 percent compressor) and the motor efficiency could be kept to 80 percent, the overall efficiency would be 64 percent. This would be considerably better than an automobile engine, which is in the 20 percent range.
For some uses, such as taxi service, this type of car may be adequate. High horsepower is not required. Rickshaws and pedicabs have been used for this type of service, with a total power available of about 1/10 horsepower.
Whether this particular design is practical may be an open question. The engine seems to be much more complex than a normal gasoline engine and it may be expensive to build and maintain. The car uses an aluminum frame, which is expensive and energy intensive. The claims for the car are probably overstated, but do not appear to violate basic Physics by a great deal.
The 46 MJ figure quoted as the stored energy in the tanks is probably a little optimistic, but in the right range.
Consider a cylinder 1 sq ft in cross section and 3750 feet long. For isothermal compression, the volume times the pressure is constant. If you move the piston in a short distance, the air pressure rises as the volume reduces. The work done can be approximated by using the average of the starting and ending air presssures times the distance the piston is moved. This can easily be done for 100 points using a spreadsheet such as Excel. There will be some error in the results, but probably only a few percent.
For a compression ratio of 300, I get that the total work required would be 31 million ft-lb, 11.75 KW-Hr, or 42 MJ.
During compression, heat must be romoved from the air to keep it at the same temperature. When the air is expanded, this heat will have to be replaced or there will be some loss in efficiency.
The usable energy in the air tank may be a little less, since the motor may not be usable when the pressure drops below a few hundred psi. This will reduce the range but will not necessarily reduce the overall efficiency.
If the charging efficiency was 80 percent (90 percent electric motor, 90 percent compressor) and the motor efficiency could be kept to 80 percent, the overall efficiency would be 64 percent. This would be considerably better than an automobile engine, which is in the 20 percent range.
For some uses, such as taxi service, this type of car may be adequate. High horsepower is not required. Rickshaws and pedicabs have been used for this type of service, with a total power available of about 1/10 horsepower.
Whether this particular design is practical may be an open question. The engine seems to be much more complex than a normal gasoline engine and it may be expensive to build and maintain. The car uses an aluminum frame, which is expensive and energy intensive. The claims for the car are probably overstated, but do not appear to violate basic Physics by a great deal.
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Chris Smith
- Posts: 4325
- Joined: Tue Dec 04, 2001 1:01 am
- Location: Bieber Ca.
And the cost to charge the air tank is?
And the efficiency ratio of compressing air into a tank is?
And the return loss from an air tank is?
And the motors efficiency is?
And the dollar per HP, per hour, per tank is?
We knew it worked over 100 years ago so the math in the above post is moot.
A little Better than back then,... but still moot unless you can gather free air at the end of the rainbow.
So far, no one has a clue on that one, .....gee, I wonder why?
Remember the completely undeniable fact that if a 50 hp compressor charges a tank for one hour, regardless of the size of the tank and pressure, you wont be getting anywhere near as much as 50 hp back and the cost of the 50 hp motor in,... per hour, wont be free or cheap any time soon not even with special Dorothy Slippers.
It still costs between 7 cents to over 25 cents per HP in,..[min] to run a motor, and a lot less bucks worth of air will be coming out.
Average cost of a hours worth of air needed to drive a 50 HP Air motor is $5.00 per hour in,...on the low side, and $17.00 per hour in,... on the high side.
And this is the sanitized version and its still only 50 HP.
No wonder there is soo much hype on the web, We have lots of hot air just for you, come to Venezuela?
So regardless of trying to compare efficiencies of air VS gas, there is none that come even close.
Gas has 100,000 BTUs per gallon or 6 pounds of weight, and at 25% return of this value, air doesn’t come any where near to giving us 25,000 BTUs worth of pay back for one gallon volume, or six pounds of weight.
Even liquid air weighs more per volume, cost more to produce, and only gives us a fraction of this value of 25,000 BTUs per gallon back.
The COST of producing power from ....[not retail]
Hydroelectric......1.1 to 7.0 cents per KW
Wind...............5.3 to 8.1 cents per KW
Electrical wind generators already cost over 1000 bucks per KW to build on land and can only produce when the wind blows for more money that the dam can do the same job for.
Then you have to convert these towers to air compressors and transport air from where the wind blows to distribution centers at what cost, then distribute the air at what cost, lose 66% of the energy you started with and then some, buy and build the stations and equipment, find the land and the labor and make a profit for all of the above as well as amortize everything.
We can waste energy any time and be a Rube with out the need of compressed air.
Remember if it sounds too good, you have been spending way too much time on the web.
And the efficiency ratio of compressing air into a tank is?
And the return loss from an air tank is?
And the motors efficiency is?
And the dollar per HP, per hour, per tank is?
We knew it worked over 100 years ago so the math in the above post is moot.
A little Better than back then,... but still moot unless you can gather free air at the end of the rainbow.
So far, no one has a clue on that one, .....gee, I wonder why?
Remember the completely undeniable fact that if a 50 hp compressor charges a tank for one hour, regardless of the size of the tank and pressure, you wont be getting anywhere near as much as 50 hp back and the cost of the 50 hp motor in,... per hour, wont be free or cheap any time soon not even with special Dorothy Slippers.
It still costs between 7 cents to over 25 cents per HP in,..[min] to run a motor, and a lot less bucks worth of air will be coming out.
Average cost of a hours worth of air needed to drive a 50 HP Air motor is $5.00 per hour in,...on the low side, and $17.00 per hour in,... on the high side.
And this is the sanitized version and its still only 50 HP.
No wonder there is soo much hype on the web, We have lots of hot air just for you, come to Venezuela?
So regardless of trying to compare efficiencies of air VS gas, there is none that come even close.
Gas has 100,000 BTUs per gallon or 6 pounds of weight, and at 25% return of this value, air doesn’t come any where near to giving us 25,000 BTUs worth of pay back for one gallon volume, or six pounds of weight.
Even liquid air weighs more per volume, cost more to produce, and only gives us a fraction of this value of 25,000 BTUs per gallon back.
The COST of producing power from ....[not retail]
Hydroelectric......1.1 to 7.0 cents per KW
Wind...............5.3 to 8.1 cents per KW
Electrical wind generators already cost over 1000 bucks per KW to build on land and can only produce when the wind blows for more money that the dam can do the same job for.
Then you have to convert these towers to air compressors and transport air from where the wind blows to distribution centers at what cost, then distribute the air at what cost, lose 66% of the energy you started with and then some, buy and build the stations and equipment, find the land and the labor and make a profit for all of the above as well as amortize everything.
We can waste energy any time and be a Rube with out the need of compressed air.
Remember if it sounds too good, you have been spending way too much time on the web.
Most of the questions in Chris's post have been answered several times.
Chris is simply too dumb to understand the answers.
Ideally, charging the tank takes 46 MJ. This is 12.78 KW-Hr. A reasonable value for the motor efficiency is 90 percent, and from the Pressure-Volume diagram on the web site, a multistage compressor should be 80 to 90 percent efficient. This would require several compression cycles with cooling in between to approximate isothermal compression. Total energy to charge the tank would be 17.75 KW-Hr assuming an 80 percent efficient compressor. Using Chris's figures of 1.1 to 8.1 cents per KW-Hr give a recharging cost of 19.5 cents to 1.44 dollars for refilling a tank.
With reasonable power cost the energy cost for refilling a tank might be in the 60 to 80 cent range. A 2.00 dollar filling charge would allow a fair amount for other business costs, such as salaries, rent and depreciation. It is not totally unreasonable.
There is no need for 50 horsepower. I know of one electric car conversion (a Volkswagen van with an overload of batteries). It was driven from coast (Pasadena, CA) to coast (Cambridge, MA). The motor was about 10 horsepower.
No one has claimed to be using liquid air, and no one has claimed that this is a high energy density system.
The overall efficiency would be the power plant efficiency (55 percent), times the motor efficiency (90 percent), times the compression efficiency (80 percent), times the air motor efficiency (possibly 75 percent). The overall efficiency would be about 30 percent. The efficiency of an automobile engine is about 20 percent. Even if the electric power was generated with fossil fuel, the air powered car would be about 50 percent more efficient than a normal car. Since the performance is scaled down, the impact on natural resources would be substantially less than a conventional car.
I note that this is being proposed for India. India has iron, coal, and thorium deposits available. Future plans in India are to shift electric power production from mostly coal fired plants to nuclear energy using a thorium fuel cycle. India does not have significant petroleum deposits. This type of car is attractive because it can be produced and powered with domestic materials and will not increase dependence on imported materials. There does not appear to be any insurmountable obstacles, since air powered vehicles were built with the technology available over 100 years ago. Incidently, that technology also included engines with multiple expansion, which gives a substantial efficiency increase for both air and steam engines.
This particular design may be less desirable because of its extensive use of aluminum. A design done in India might use either steel or composite materials to make it more compatible with domestic resources.
Chris is simply too dumb to understand the answers.
Ideally, charging the tank takes 46 MJ. This is 12.78 KW-Hr. A reasonable value for the motor efficiency is 90 percent, and from the Pressure-Volume diagram on the web site, a multistage compressor should be 80 to 90 percent efficient. This would require several compression cycles with cooling in between to approximate isothermal compression. Total energy to charge the tank would be 17.75 KW-Hr assuming an 80 percent efficient compressor. Using Chris's figures of 1.1 to 8.1 cents per KW-Hr give a recharging cost of 19.5 cents to 1.44 dollars for refilling a tank.
With reasonable power cost the energy cost for refilling a tank might be in the 60 to 80 cent range. A 2.00 dollar filling charge would allow a fair amount for other business costs, such as salaries, rent and depreciation. It is not totally unreasonable.
There is no need for 50 horsepower. I know of one electric car conversion (a Volkswagen van with an overload of batteries). It was driven from coast (Pasadena, CA) to coast (Cambridge, MA). The motor was about 10 horsepower.
No one has claimed to be using liquid air, and no one has claimed that this is a high energy density system.
The overall efficiency would be the power plant efficiency (55 percent), times the motor efficiency (90 percent), times the compression efficiency (80 percent), times the air motor efficiency (possibly 75 percent). The overall efficiency would be about 30 percent. The efficiency of an automobile engine is about 20 percent. Even if the electric power was generated with fossil fuel, the air powered car would be about 50 percent more efficient than a normal car. Since the performance is scaled down, the impact on natural resources would be substantially less than a conventional car.
I note that this is being proposed for India. India has iron, coal, and thorium deposits available. Future plans in India are to shift electric power production from mostly coal fired plants to nuclear energy using a thorium fuel cycle. India does not have significant petroleum deposits. This type of car is attractive because it can be produced and powered with domestic materials and will not increase dependence on imported materials. There does not appear to be any insurmountable obstacles, since air powered vehicles were built with the technology available over 100 years ago. Incidently, that technology also included engines with multiple expansion, which gives a substantial efficiency increase for both air and steam engines.
This particular design may be less desirable because of its extensive use of aluminum. A design done in India might use either steel or composite materials to make it more compatible with domestic resources.
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Chris Smith
- Posts: 4325
- Joined: Tue Dec 04, 2001 1:01 am
- Location: Bieber Ca.
This is where your fantasy falls apart...
With reasonable power cost the energy cost for refilling a tank might be in the 60 to 80 cent range.
[In the land of OZ perhaps?]
A 2.00 dollar filling charge would allow a fair amount for other business costs, such as salaries, rent and depreciation. It is not totally unreasonable.
It is way past absurd, all the way to stupid.
Try 5 to 15 bucks per hour, and with only a 50 hp motor production, and you may start to get a little closer to reality.
At over 7 cents per hp/ hr to fill, [and up wards or four times this at todays prices and more for wind generation of compressed air] your costs are up there with Alice in wonderland.
At a discount rate which wont be happening any time soon,....$2.00 worth of air is 20 to 28 KW worth of energy which when translated into HP is 11 hp per hour and even less when you consider all of the real losses.
So why don’t you show us where your rainbow can be found, preferably the free tank at the end of the rainbow.
And some here actually cant do the math, much like your proposal above.
Your units of measure are moot, useless, and irrelevant because you cant count the energy necessary to fill a tank and how much return you will get in exchange.
Mentioning MJs is at best a lousy smoke screen so you can avoid the real costs of filling up the air tank.
But you do tell a good pipe dream.
With reasonable power cost the energy cost for refilling a tank might be in the 60 to 80 cent range.
On what planet?
With reasonable power cost the energy cost for refilling a tank might be in the 60 to 80 cent range.
[In the land of OZ perhaps?]
A 2.00 dollar filling charge would allow a fair amount for other business costs, such as salaries, rent and depreciation. It is not totally unreasonable.
It is way past absurd, all the way to stupid.
Try 5 to 15 bucks per hour, and with only a 50 hp motor production, and you may start to get a little closer to reality.
At over 7 cents per hp/ hr to fill, [and up wards or four times this at todays prices and more for wind generation of compressed air] your costs are up there with Alice in wonderland.
At a discount rate which wont be happening any time soon,....$2.00 worth of air is 20 to 28 KW worth of energy which when translated into HP is 11 hp per hour and even less when you consider all of the real losses.
So why don’t you show us where your rainbow can be found, preferably the free tank at the end of the rainbow.
And some here actually cant do the math, much like your proposal above.
Your units of measure are moot, useless, and irrelevant because you cant count the energy necessary to fill a tank and how much return you will get in exchange.
Mentioning MJs is at best a lousy smoke screen so you can avoid the real costs of filling up the air tank.
But you do tell a good pipe dream.
With reasonable power cost the energy cost for refilling a tank might be in the 60 to 80 cent range.
On what planet?
On the Earth.
The Pressure-Volume diagram shows fairly clearly how the efficiency can be improved by using several expansion steps with added heat rather than a single adiabatic expansion. A similar technique can be used to improve the compression efficiency.
There is no "automatic" 33 or 66 percent loss in either compression or expansion. The amount of loss can be reduced substantially by using several stages of compression or expansion and removing or adding heat between the stages.
Engines with multiple expansion for both steam and air were built and used in the nineteenth century. It isn't a new or impossible idea.
Most of this is covered by the Ideal Gas Law:
P*V = n*R*T
P is pressure
V is volume
n is moles of gas
R is a constant
T is absolute temperature
Work is represented by area on a Pressure-Volume diagram
The Pressure-Volume diagram shows fairly clearly how the efficiency can be improved by using several expansion steps with added heat rather than a single adiabatic expansion. A similar technique can be used to improve the compression efficiency.
There is no "automatic" 33 or 66 percent loss in either compression or expansion. The amount of loss can be reduced substantially by using several stages of compression or expansion and removing or adding heat between the stages.
Engines with multiple expansion for both steam and air were built and used in the nineteenth century. It isn't a new or impossible idea.
Most of this is covered by the Ideal Gas Law:
P*V = n*R*T
P is pressure
V is volume
n is moles of gas
R is a constant
T is absolute temperature
Work is represented by area on a Pressure-Volume diagram
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Chris Smith
- Posts: 4325
- Joined: Tue Dec 04, 2001 1:01 am
- Location: Bieber Ca.
In other words, you don’t have a clue, but the fancy smoke and mirrors of the web keeps you happy?
The Pressure-Volume diagram shows fairly clearly how the efficiency can be improved by using several expansion steps with added heat rather than a single adiabatic expansion. A similar technique can be used to improve the compression efficiency.
"with added heat"?
More free energy?
Too bad physics makes you dizzy, you could do your own math and stop pretending all of these web sales are going to solve your problems.
There is no "automatic" 33 or 66 percent loss in either compression or expansion. The amount of loss can be reduced substantially by using several stages of compression or expansion and removing or adding heat between the stages.
Really, again in what world.
Physics isn’t going to change for you, your statement, or anything else.
Its called “The Laws of Physicsâ€
The Pressure-Volume diagram shows fairly clearly how the efficiency can be improved by using several expansion steps with added heat rather than a single adiabatic expansion. A similar technique can be used to improve the compression efficiency.
"with added heat"?
More free energy?
Too bad physics makes you dizzy, you could do your own math and stop pretending all of these web sales are going to solve your problems.
There is no "automatic" 33 or 66 percent loss in either compression or expansion. The amount of loss can be reduced substantially by using several stages of compression or expansion and removing or adding heat between the stages.
Really, again in what world.
Physics isn’t going to change for you, your statement, or anything else.
Its called “The Laws of Physicsâ€
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positronicle
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Chris Smith
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- Location: Bieber Ca.
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positronicle
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Chris Smith
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