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Author Topic: How does one modify a 4-stroke engine to run on compressed air?  (Read 5680 times)

Offline CliffordK

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This question was sent to me via PM mail.  With a little effort to write up an answer, I thought it was better to answer in the forum.

Quote
Sir,
Can you tell me how to modify the cam of a 4 stroke engine to run on compressed air..?????


 

Offline CliffordK

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In a 4-stroke engine, the crank turns through two complete revolutions for every cycle while the cam turns only a single revolution.

(Piston Motion)
Down - Intake (intake valve open)
Up - Compression (both valves closed)
Down - Power (both valves closed)
Up - Exhaust. (exhaust valve open)


An air compressor or an air engine only requires 2 cycles, or one crank revolution.

Most piston-type air compressors are built with one-way flapper valves and no cam shaft. 
(Piston Motion)
Down - Intake (intake valve opens due to suction, and exhaust valve is closed)
Up - Compression (intake valve closes with pressure, and the pressure pushes the exhaust valve open).


Your air engine would probably require some kind of an active valve system. 
Down - Power (intake valve is open)
Up - Exhaust (exhaust valve is open).

One could accomplish this in a couple of ways.  Using the standard 2:1 Crankshaft to cam ratio, one would put on 2 lobed cams, for the intake and exhaust, oriented 90 degrees from each other.

If the camshaft timing gear and crankshaft timing gear was the same size giving a 1:1 crankshaft/camshaft ratio, one would grind hemisphere lobes on the cam.



Using standard valves, your intake pressure would be limited by the valve spring strength on the intake valve.  One might want extra strength springs.  One could redesign the head to flip the intake valve so that it opened towards the pressurized intake manifold, and thus allow higher pressure.

However, it might be better to design some kind of either rotary valve or sleeve valve.



Thus allowing higher intake manifold pressure.

I believe the reason this isn't used in modern automobiles is that the combustion chamber would be harsh on the sleave valves.  An air engine, however, would not have the caustic combustion chamber, and could effectively utilize the rotary or sleeve valves.
« Last Edit: 03/08/2013 07:55:58 by CliffordK »
 

Offline Lmnre

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Okay, so how would the engine or vehicle operator control the power being produced? We wouldn't want to drive around with maximum power all the time. The carburetor wouldn't be necessary because there's no need to regulate the fuel/air mixture, right?
 

Offline CliffordK

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Correct,
If one was using an ordinary engine, just add the air supply to the intake manifold.

Power, on/off, etc can all be regulated with a simple valve to vary the air flow/pressure/volume.

 

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