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Old 09-24-2013, 07:58 PM   #1 (permalink)
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Air/gas engine hybrid idea

I'm planning on taking the back three cylinders in my inline six and running them off of compressed air, the idea is that it would increase low end torque will also allowing me to remove the starter cause one of thoughs cylinders will always be in the power stroke so to start all you have to do is open the compressed air valve. I'm in construction so I have a compressor to maintain compression the only things that come to mind that I'm going to have to do is buy a special camshaft(about $180) cut the back three ports off the intake manifold and manufacture a manifold for the back cylinders, and then get the fittings to adapt the compressor to my jeep and control throttle. Any thoughts on this??

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Old 09-24-2013, 08:23 PM   #2 (permalink)
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My first though is that you're going to need to use higher pressure air than that typically used for use with air tools, both in order to get useful power out of those cylinders and to be able to store a useful amount of energy. Dive cylinders might do it, if you can figure out a way to control the air at those sort of pressures..
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Old 09-24-2013, 10:28 PM   #3 (permalink)
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I'm planning on buying a 400psi compressor, it has a 400psi side for curtain tools and a 150psi side for the tools I already have! Do you think that's enough pressure??
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Old 09-25-2013, 12:41 AM   #4 (permalink)
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I don't think so but maybe.

As a quick first pass assessment, if you assume:

An air tank volume i.e. V1, of 100 liters (26 US gallons)

Adiabatic expansion (no losses), so not realistic.

Between:

Tank pressure, P1 = 400psi = 2775 kPa

and

Atmospheric pressure, P2 = 14.7 psi = 100kPa.

k for air = 1.4.

Using: P1*V1^k = P2*V2^k

Gives V2 =0.714 m^3

Plug that into:

w = [(P1*V1)-(P2*V2)]/(1-k)

Gives work = 417.5 kJ

At a rate of 4kW = 4kJ/s, that will last a little more than 100 seconds. At 40kW, 10 seconds.

Last edited by Occasionally6; 09-25-2013 at 07:30 AM..
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Old 09-25-2013, 01:48 AM   #5 (permalink)
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You may be thinking about a setup similar to what was done in opal mining zones in Australia, where Beetle engines were repurposed to be used as stationary air compressors for pneumatic tools. 2 cylinders remained working as they were designed to, while 2 others were reconfigured to 2-stroke and used only to compress air. Actually, if I were you I'd rather get a 4-cylinder engine for the Jeep and bolt an air compressor into that.

BTW if you're considering to use pneumatic power to move the vehicle, you should search for that prototypes released recently by Peugeot and CitroŽn with a pneumatic auxiliary drive as an alternative to the electric auxiliary drive which got mainstream in production hybrids.
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Old 09-25-2013, 04:13 AM   #6 (permalink)
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How will you power the compressor? I do not have any idea why, but I once figured out how much air an engine needs, wondering about using it in a vacuum or something, and storing enough air to use for combustion was unrealistic. As Occasionally6 demonstrated, air-powering an engine would not really work with tanked air.

I think that cRiPpLe_rOoStEr had an interesting contribution, using an ICE to compress air and the Peugeot and CitroŽn prototypes.

People often said that if crazy ideas work, then every car manufacturer would be using them.

Except my mother. She is a conspiracy theorist and insists that people have invented far more efficient engines, great hydrogen-cell systems, etc, the oil companies did not like them, and they disappeared. However, one of my professors mentioned a friend that came up with an oil system for cars that would last much longer. He was sued until he went bankrupt and then they bought his patent.

Maybe his system was not so much better. Perhaps he could have proved that it lasted 7,500 miles, while most people tell you to change it every 3,000 miles.

Anyway, I think that there is plenty of room for innovation. Not all ideas are viable, though. Hopefully, our friends here can give you more feedback.
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Old 09-25-2013, 07:44 AM   #7 (permalink)
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Quote:
Originally Posted by Xist View Post
How will you power the compressor? I do not have any idea why, but I once figured out how much air an engine needs, wondering about using it in a vacuum or something, and storing enough air to use for combustion was unrealistic.
I've done the same; there are not too many truly new ideas . It might be made to work in drag racing, used like N2O, but dive cylinder type pressures are still required to get a reasonable mass of air.

Using the stored air for supercharging has been tried. There are a couple of SAE papers on it (written in the '50's?).

The initial variant used an air ejector above the carburettor to provide the compressed air. (You've probably seen an air ejector if you've watched an F1 race; they're the short tubes connected to airlines they use to cool the drivers.)

The later version used additional poppet valves in the cylinder head to inject the high pressure air directly into the cylinder, after the normal inlet valve had closed.

The idea was to use a downsized engine and save some fuel when the extra power wasn't being used.

An auxiliary compressor was attached to the engine and a (large) high pressure storage tank installed in the trunk.
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Old 09-25-2013, 07:58 AM   #8 (permalink)
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I don't know how close you want to get to the same sort of torque your engine can make but using the lower end of peak cylinder pressures during combustion your compressor would need to be able to compress 53000 liters of air a minute to about 290psi,thats at 1500rpm. I don't know what compressor your using but that sounds like a pretty big compressor to me.
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Old 09-25-2013, 10:05 AM   #9 (permalink)
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Quote:
Originally Posted by Xist View Post
How will you power the compressor? I do not have any idea why, but I once figured out how much air an engine needs, wondering about using it in a vacuum or something, and storing enough air to use for combustion was unrealistic. As Occasionally6 demonstrated, air-powering an engine would not really work with tanked air.

I think that cRiPpLe_rOoStEr had an interesting contribution, using an ICE to compress air and the Peugeot and CitroŽn prototypes.

People often said that if crazy ideas work, then every car manufacturer would be using them.

Except my mother. She is a conspiracy theorist and insists that people have invented far more efficient engines, great hydrogen-cell systems, etc, the oil companies did not like them, and they disappeared. However, one of my professors mentioned a friend that came up with an oil system for cars that would last much longer. He was sued until he went bankrupt and then they bought his patent.

Maybe his system was not so much better. Perhaps he could have proved that it lasted 7,500 miles, while most people tell you to change it every 3,000 miles.

Anyway, I think that there is plenty of room for innovation. Not all ideas are viable, though. Hopefully, our friends here can give you more feedback.
Current oil systems allow for 7,500+ miles. I change mine every 8,000, the same time I rotate tires. The 3000 mile mark is a conservative one, usually recommended for vehicles that do mostly city driving. Most people cite that number because oil changes are cheap, its the one thing you do that effects engine longevity the most, and why not use the most conservative interval.

As for the air powered engine, gasoline combustion is going to be more efficient and practical. To produce the amount of air required you would need an on board compressor that uses electricity or gas. If you go electric you need to buy batteries, find a way to charge them, etc. Using gas to power a compressor to replace gas is counter intuitive, as gas combustion would be more efficient. Electricity still costs money, and I tend to believe that powering an air compressor to power the engine, rather than using an electric motor, is less efficient therefore will just be more trouble than it's worth.
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Old 09-25-2013, 10:16 AM   #10 (permalink)
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Quote:
Originally Posted by Xist View Post
Maybe his system was not so much better. Perhaps he could have proved that it lasted 7,500 miles, while most people tell you to change it every 3,000 miles.
Oil technology has evolved a bit.

Maybe it's time for the US to get along a bit , and change to a more realistic oil change interval ?
Yes, you can ...

The minimum we have in Europe on current cars is 15000 km - 9500 miles.
20 to 30000 km is quite normal here - that's 12500 to 19000 miles

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