Using a multicylinder engine as a compressor

[cheb]

Has anyone tried this? The Americans used V8 engines, one bank running normally for power, the other purely as an air compressor, no fuel nor sparks, as a air supply for surface supplied air scuba diving

I'm sure there's lots of reasons why it's not done, but it's an interesting concept, well, to me at least.

 

[Ruffian]

Seen old engine linked to another engine flywheel to flywheel,
One as a driven engine one as a pump.
Driven engine was old k10 micra if I remember correctly.

Cant remember what the other engine was but had exhaust cam bypassed and one way valve in the spark plug holes.

 

[brightspark]

probably not worth doing unless its a decent size and then u need a decent size motor . would have to be diesel or petrol unless you have 3 phase supply

 

[DAPPH]

Way back in the stone age 51 yrs ago out in Germany I visited a Canadian barracks & popped into their forces shop at Zoest which was like an Aladdin's cave .

I purchased a nifty little device that you screwed in place of a spark plug , left the HT lead off and started the engine . On every compression stroke of the cylinder it was fitted to it pushed a small piston up to compress about 20 cc of clean air .
Good enough to inflate a car tyre in 4 min or so and good enough to operate a small spark plug grit blaster .

Both items came as a set with a small bag of grit IIRC .

 

[Shox Dr]

Worth searching the forums, it was discussed in detail many moons ago

 

[brightspark]

remember my brothers mate making one out of a triumph t10 engine what a waste

 

[Rig Pig]

I seem to remember something about vw beetle engines making good 2 cylinder self powered compressors, think it was on here.

 

[Greg05]

I seem to remember something about vw beetle engines making good 2 cylinder self powered compressors, think it was on here.

I have seen that in the past too, if I remember correctly I think it's called volks-air

 

[minimutly]

I had rountuit plans in my head years ago - ford crossflow (flat head), using 1 and 2 pots, with spring loaded poppet valves instead of using the cam. No reason it wouldn't work.

 

[Screwdriver]

I can see the attraction of using an engine to compress air directly, seems neat. Just wondering what the efficiency of a regular 4 cycle might be unless the “compressor” cylinders have radically altered valve timing. Surely it would be much better just to bolt a regular compressor to an engine?

 

[CompoSimmonite]

What you want is a Cadillac V8-6-4 engine. It's a V8 that will also run as a V6 and V4 when all the power not required

 

[Seadog]

Just wondering what the efficiency of a regular 4 cycle might be unless the “compressor” cylinders have radically altered valve timing.

If each cylinder has a separate inlet and exhaust port, remove the rockers for those cylinders and fit non-return valves to the ports, one allowing ingress and the other egress.

 

[Screwdriver]

If each cylinder has a separate inlet and exhaust port, remove the rockers for those cylinders and fit non-return valves to the ports, one allowing ingress and the other egress.

Hmm but surely if a regular petrol/diesel engine isn’t designed specifically to compress air, it will be severely compromised no matter what you do? The compression ratio and shape of the cylinder head/squish would affect efficiency, plus half your compressor would be twostroking so half the compression cycle would be relying on the flywheel as the engine tries to exhaust the spent combustion and simultaneously compress air. Seems fraught and your mpg is going to be horrendous.

 

[eddie49]

https://www.mig-welding.co.uk/forum/threads/these-compressors-sufficient-for-blasting.27938/

 

[minimutly]

Hmm but surely if a regular petrol/diesel engine isn’t designed specifically to compress air, it will be severely compromised no matter what you do? The compression ratio and shape of the cylinder head/squish would affect efficiency, plus half your compressor would be twostroking so half the compression cycle would be relying on the flywheel as the engine tries to exhaust the spent combustion and simultaneously compress air. Seems fraught and your mpg is going to be horrendous.

I thought I spelled it out above - flat head, spring loaded poppet valves instead of using the cam - sigh....
But if you want to waste 2 strokes fine, use the cam. Who is going to drive around using this?

 

[R Kraft]

Way back in the stone age 51 yrs ago out in Germany I visited a Canadian barracks & popped into their forces shop at Zoest which was like an Aladdin's cave .

I purchased a nifty little device that you screwed in place of a spark plug , left the HT lead off and started the engine . On every compression stroke of the cylinder it was fitted to it pushed a small piston up to compress about 20 cc of clean air .
Good enough to inflate a car tyre in 4 min or so and good enough to operate a small spark plug grit blaster .

Both items came as a set with a small bag of grit IIRC .

One of these ?
http://www.aerostich.com/media/cata...06319eda06f020e43594a9c230972d/3/5/3570li.jpg

 

[frank horton]

loadsa flow but little pressure......don't bother......ud be better off with a comp from Lidil......
did see a Harley 45engine converted.....again what a waste.....

 

[Screwdriver]

I thought I spelled it out above - flat head, spring loaded poppet valves instead of using the cam - sigh....
But if you want to waste 2 strokes fine, use the cam. Who is going to drive around using this?

Sigh all you like mate but you are not understanding the obvious problem with using a poppet valve. A four stroke engine opens the exhaust valve once every four strokes without "radically altering the port timing" as I said earlier. Stick a poppet on there and the exhaust/compressor valve will operate every two strokes, it will be similar to "twostroking" which is a technical term for a specific problem in a four stroke engine.

The upshot is, the four stroke engine will be pressurising the compressor tank twice per crankshaft revolution with the modified cylinder when it will only producing power once for each unmodified cylinder. On top of that, the modified cylinder will be operating against the compressor tank pressure every time the driving piston needs to compress the fuel charge. Plus a modern engine relies on a technical phenomena I have little practical knowledge of called scavenging. It is of course a property of gas flow which optimises the evacuation of a cylinder due to the swirl created by a flame front. That phenomena relies on not only the design of the cylinder head shape but also some subtleties of valve timing where the engine is optimised for a specific rpm range. Actual valve timing is based on the characteristics of combustion gas flow meaning an exhaust valve might actually be open slightly during the compression cycle before tdc and prior to ignition. How that effects the efficiency of its use as a compressor cylinder is a non trivial problem (I suggest).

There are a number of interesting problems with this nominally simple idea, not the least of which being, at what pressure will the compressed air in the cylinder balance with the pressure in the compressor tank. You can't rely on pressure pulses to effectively "close" an open exhaust valve with a shock wave (which is how a four stroke engine uses back pressure returning from the exhaust pipe) and you certainly can't casually assume an actual two stroke would even run without these complex shock waves controlling port timing. A two stroke engine would probably sit there chuffing air in and out of its ports since it relies almost entirely on the expansion chamber sending a high pressure "echo" from the reverse cone to slam the ports shut.

If you sit and think about what is actually happening inside an engine, it becomes an extremely challenging question. I suspect this is what cheb is flagging up as "interesting" about the concept.

 

[minimutly]

You need to stop telling me what I don't understand, and making problems out of what you don't.
Two stroke compressor and four stroke engine - perfect. Why wouln't it work? Well pulse tuning isn't going to stop it that's for sure.
Compressing the air whilst compressing the charge - no problem I see, the engine isn't pushing you up a hill, after all.
You allmost make me want to build it to prove you wrong, but life's too short.

 

[mtt.tr]

screwdriver has woken up in a bore you to death with long replies consisting mostly of google