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Author Topic: can petrol engine covert into air compressed engine? pls help  (Read 7101 times)

Offline josh123

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Hi
 i was just thinking about the petrol engine when the piston goes up and down it produce compressed air
why cant we store that air directly to a tank and pump the air into the piston head .so the engine can run with air after
felling the air tank with petrol for once ..
will it work ... sorry if its stupid ?



 

Offline CliffordK

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If you are using the engine for 100% compressed air, then you might choose to regrind the cam to make a 2-stroke engine.

Air Engine:
Open intake valve on downstroke.  Close somewhat before the bottom of the stroke.
Open exhaust valve on upstroke.  Close at TDC.

Compressor
Same as above, but intake from open air, exhaust into compressor tank.

Note, a compressor normally uses a spring loaded passive valve system in which a vacuum opens the intake valve, and pressure opens the exhaust valve.

Jake Brakes and Exhaust Brakes are often used on Diesel engines, and could potentially be routed into a compressor, or compressor exchange system.  Or, to avoid complications with using exhaust heat and exhaust gases, one might route a turbocharger into a compressor when one desires energy recovery.

Some manufactures have been experimenting with Camless Solenoid Valve Engines.  These might be beneficial for the engines that are used as compressor/air engines for braking energy recovery systems.
 

Offline peppercorn

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If you are suggesting the compressed air tank (usually called an accumulator) simply acts as a store of energy (just like an electric battery) then there are more efficient approaches (though not many simpler) to storing energy for later use.

But remember that any change of energy from one type (eg. mechanical force from combustion pushing down on the piston) to another type (eg. air being pumped into a high pressure accumulator) will never return 100% of the energy that was available to begin with (esp. with compressed air as the air will heat up as compressed and any cooling whilst stored will reduce it's ability to do work later on).

There has to be a very good reason to bother to store energy (ie. the ability to carry out work) in a machine, because you are going to pay a price for doing so.   The only reason hybrid vehicles make sense is a piston engine is far less efficient at part load.  So the battery pack gives the control system the ability to shift the time that the piston engine is working to either an all or nothing situation (ie. it's Fully On/working hard or Fully Off/not working at all).
[I'm sure some bright spark's going to pick me up on this description, so I'll just add that this is only meant as an introductory outline of a hybrid's operation and there are also other factors involved ::) ]
« Last Edit: 12/05/2012 17:10:29 by peppercorn »
 

Offline Geezer

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As Clifford says, with some modifications, it should be possible. I think this method of energy storage is not used on vehicles because it is not very efficient. Unless you compress the air very slowly it gets quite hot, and the heat produced is usually lost to the atmosphere. The energy density is also very small, so you need a really big storage tank to produce a reasonable amount of mechanical energy (work).

There actually are/were locomotives used in mines that operate on stored compressed air. Also, there are large scale compressed air storage systems (link attached).

http://en.wikipedia.org/wiki/Compressed_air_energy_storage
 

Offline CliffordK

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How about this...
With a Diesel engine in stop & go traffic...

One might be more inclined to use turbo gain during hard accelerations.
So,
Use the turbo to compress air for braking.
Then shunt over to use the compressed air for acceleration, without using the boost (and loss of energy) generated by the turbo.

As far as pure compressed air engines.
I believe some people have experimented with running a vehicle with pure compressed air, or perhaps liquefied oxygen or nitrogen.  As Geezer mentions, there are significant problems with density and thermal changes.
 

Offline Geezer

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I think the efficiency and density won't justify the cost and weight.

The US gov. went to some lengths to encourage industry to abandon air powered tools and switch to electric tools because of the very low efficiency of air.
 

Offline josh123

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many thanks for all the infos

 

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