Engine derived compressor, power calculations and motorcycle donor

[normspanners]

The rings must seal to start compressing the fuel/air mixture before its ignited though so I don't see why it wouldn't work? There are lots of other issues to overcome I agree but I don't think the rings sealing is one of them.

Agreed

Take a look at the piston from a compressor pump, and note that the compression ratio is far higher than an IC engine, and that the ring set up is very different.

The piston rings in most of the pumps I have seen have been exactly like IC engine rings and I have repaired pumps with ic rings that have fitted the compressor pistons, usually used the second ring as it is thicker, when the comp parts where unavailable and as most engines normally max out from 150 up to 200 for a competition engine, I agree also, and dont see the issue, the main difference between compressor and ic are that compressors dont have positive bore lube as engines do, so dont require an oil scraper ring.
At the end of the day an engine is a compressor, especially a diesel coz thats how it works.
If an engine pump as is, gives 150 or 10 bar I dont see the need to make it go higher because most compressors stop at 10bar anyway.
And with the volksair, if using equal sized cyl you dont want the compressor to be too efficient anyway because the power side of the engine wont handle powering it.

 

[normspanners]

And with the volksair, if using equal sized cyl you dont want the compressor to be too efficient anyway because the power side of the engine wont handle powering it.

hang on a minute----------- just thought----------- the volkair unit's cant work??!! coz they use standard VDub cyl and pistons and rings, they must be just a figment of my imagination, sorry chaps for suggesting one ---- I just got carried away with the idea.

Just had a dig...http://www.mig-welding.co.uk/forum/threads/diy-blasting-compressor.39815/
Crips...three years ago.. Must get on and finish it off Been lots to do elswhere..

and yours wont work either kempi

 

[8ob]

Vaguely related to the original post.
Q; could you use the crank case pressure from either a parallel or boxer twin motor as a kind of pulsed turbocharger?
Ok I know a boxer is effectively a parallel twin. Loads of work and pressure going to waste in my book. or rather my tiny mind. The world is probably lucky that I am not an engineer. This has been stewing for donkeys years.

Most engines have as many pistons going up the bore as they do coming down at any one time which cancels out crankcase pressure. The only pressure kicking about is a bit of blowby. The only engine I can recollect having pistons bobbing up and down together was my old triumph 650 twin.

Bob

 

[normspanners]

Most engines have as many pistons going up the bore as they do coming down at any one time which cancels out crankcase pressure. The only pressure kicking about is a bit of blowby. The only engine I can recollect having pistons bobbing up and down together was my old triumph 650 twin.

Yamaha's big bang theory
two strokes use crankcase pressure to run but it is minimal, so stick to bending metal chunko!!!

 

[chunkolini]

Triumphs, BSA's, or Boxer twins, in out in out, up and down up and down; always in pairs!!!!!! a lot of air being moved pointlessly.
Crank Case breathers? they must shift some pointless energy.
Why has nobody spotted this before?

 

[normspanners]

Triumphs, BSA's, or Boxer twins, in out in out, up and down up and down; always in pairs!!!!!! a lot of air being moved pointlessly.
Crank Case breathers? they must shift some pointless energy.
Why has nobody spotted this before?

some engines run a negative pressure crank case ie a vacuum especially dry sump ones that normally have two scavenge pumps pulling on the underside of the pistons to create more power and lesson the pumping load.

 

[PhillipM]

Yeah, my buggy for one

A lot of serious race engines have transfer ports undercut into the cylinder walls to reduce pumping losses by helping the flow between adjacent pistons.

 

[Chris Stevens]

^^ the plug hole

Sure there will be pressure at the plug for a short time on a 4T motor, but only for a limited amount of crankshaft rotation, and obviously a need for a method of preventing loss of pressure when intake or exhaust valves open.

But the fact a 4T IC engine takes 720 degrees of crankshaft

Agreed


The piston rings in most of the pumps I have seen have been exactly like IC engine rings and I have repaired pumps with ic rings that have fitted the compressor pistons, usually used the second ring as it is thicker, when the comp parts where unavailable and as most engines normally max out from 150 up to 200 for a competition engine, I agree also, and dont see the issue, the main difference between compressor and ic are that compressors dont have positive bore lube as engines do, so dont require an oil scraper ring.
At the end of the day an engine is a compressor, especially a diesel coz thats how it works.
If an engine pump as is, gives 150 or 10 bar I dont see the need to make it go higher because most compressors stop at 10bar anyway.
And with the volksair, if using equal sized cyl you dont want the compressor to be too efficient anyway because the power side of the engine wont handle powering it.

Radial pressure on compressor piston rings is in almost all cases higher than the 1mm section rings used in modern IC engines, as the compressor rings are in most cases 2mm or more section, and need the higher radial pressure as there is no rapidly expanding combustion gases to push the rings out against the cylinder wall.

Compression ratio on modern petrol IC engines is about 11:1 max, while those used on piston compressors are likely to be at least 15:1 or more, as this makes the pump more efficient and helps generate more pressure more quickly.

 

[normspanners]

Sure there will be pressure at the plug for a short time on a 4T motor,

the same 180deg that a compressor does and when the inlet valve is open it is filling the cyl the same as a compressor, in the case of a normal 4T with out modifying a standard engine the 'gap' may be not such a bad thing allowing rest time for the flywheel to build up energy if using two of a four or using identical engines the compressor engine might load the driver too much ----pumping on every stroke.
I think you need to ring volkair and break it too them that their idea, that they sell at the moment wont work.

 

[rtbcomp]

Sure there will be pressure at the plug for a short time on a 4T motor, but only for a limited amount of crankshaft rotation, and obviously a need for a method of preventing loss of pressure when intake or exhaust valves open.

....

Pressure starts building from BDC to TDC. If it doesn't that means air is going somewhere, if the piping is right that somewhere is the tank.

On the compression stroke the valves are closed anyway, on the exhaust stroke the exhaust valve will be closed if the camshaft/rockers/whatever are disabled, a point made early on in the thread. Connecting cylinders 1&4 and 2&3 via the plug holes means both cylinders of a pair work in parallel.

 

[normspanners]

When two of a four cyl engine go down as in the case of a wasted spark coil ingnition system you will be very lucky to get the car to move, because there is VERY little power left over from the two powered cyl's, running the two dead ones as compressors. It will JUST run the car but not up a hill, so if those pumping cyl's where to be modified to pump fully every stroke there would be no chance of it moving which leads me to think the split is quite even ie the power required is equal to the load.Espiecially when taking the extra loading on the driven engine water /oil pumps, the charging system etc then you have to drive the air cooling system whether it be mech or electric into consideration .

 

[Chris Stevens]

the same 180deg that a compressor does and when the inlet valve is open it is filling the cyl the same as a compressor, in the case of a normal 4T with out modifying a standard engine the 'gap' may be not such a bad thing allowing rest time for the flywheel to build up energy if using two of a four or using identical engines the compressor engine might load the driver too much ----pumping on every stroke.
I think you need to ring volkair and break it too them that their idea, that they sell at the moment wont work.

Interesting...................always thought 4T cycle was 720 degrees of crank rotation?

 

[normspanners]

Interesting...................always thought 4T cycle was 720 degrees of crank rotation?

it is obviously----- but is still compressing for 180deg -----------same as a compressor.

 

[Chris Stevens]

some engines run a negative pressure crank case ie a vacuum especially dry sump ones that normally have two scavenge pumps pulling on the underside of the pistons to create more power and lesson the pumping load.

Main reason dry sump systems run at negative pressure is to evacuate oil as quickly as possible and reduce power losses related to windage.

 

[Chris Stevens]

it is obviously----- but is still compressing for 180deg -----------same as a compressor.

I would guess very few modern engines are running cams which mean 180 deg compression stroke.......................

 

[Johnseat]

Usually a little less than 180, open after tdc so a vacuum inside the chamber helps pull in the fuel air mixture for better mixing and closes just before bdc.
Somewhere in the 160 range is more realistic but you still get as much air in due to the vacuuming.

 

[KemppiFrog]

After reading this thread, I feel I have built Schrödinger's Compressor.

 

[Crater Creator]

After reading this thread, I feel I have built Schrödinger's Compressor.

Yeah from this thread it would appear there is an equal chance of your compressor both existing and not existing. Similar odds to leaving your garage door open for 10 minutes in Glasgow.

 

[KemppiFrog]

Just to clarify. While building it, I did not expect top efficiancy. But using a 75hp engine driving a 4 pot 1250cc engine, would allow me to ignore the lower compression ratio of 9.5:1 because I did not fill up the compustion chamber and any other inefficiencies due to the NRVs not giving a high flow rate and, it seems, that my piston rings don't seal too well. Reality is, it whacks out a lot of air.
Reminds me of the guys at the Lockheed Skunk Works.. We can make it 80% efficient, the other 20% is too expensive/difficult to achieve, so we go with what works.