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Self Supercharging engine
3

Self Supercharging engine

Self Supercharging engine

(OP)
Last night during a bench racing session, some friends and I discussed a concept that was new to us. I assume that it has been tried somewhere by someone (as almost everything has thanks to Smokey). Anyone please speak up, as this is probably tragically flawed.

There is a class that limits engines to four cylinders and forbids turbochargers and superchargers, but does not specify Natural Aspiration strictly. What if you took a V8 engine and used the exhaust charge from four cylinders to compress the intake charge for the other four cylinders? Let me explain a little more. It would have to be direct injected, the 'compressor' side would have no ignition, just air in, compression, and release compressed air thru a one way flow control of some sort into a chamber to be used in the intake charge of the other four cylinders. Understanding that there would be energy wasted in running the piston thru the power stroke without actually making power, do you think the power increase from the charged intake would overcome the power losses of swinging that heavier mass(8 cyl VS 4 cyl) and the wasted power stroke of the compressor side.

RE: Self Supercharging engine

I suppose you could feasibly make it work. But based on the rules, I'd doubt they'd let you run, even if the other 4 aren't combusting fuel.

RE: Self Supercharging engine

The other four are a supercharger.  Period. And probably a low-efficiency one.

RE: Self Supercharging engine

I've worked on a few self super charging designs, everyone I've worked on required reed valves to push the energy balance towards positive, poppets are too complex, and waste energy.

There is a thread about SBC compressors, where half the motor is a compressor for air, while the other half powers it.


I dont think that normal head/piston/valve geometry is a very efficient way to compress things. There is way too much dead space at the top of the stroke. (You could modify the head to eliminate these problems.)

Interestring thought, though I dont know how well a SI motor would handle 2x the air from 0rpm till whenever the rpm's are too high for the whole second bank compressed intake air to move across.

Nick
I love materials science!

RE: Self Supercharging engine

The cam on the comperssor side would be 1 times rpm, so you would get 2 times the air.  You would dome the piston for very little clearance.  Sounds interesting.  

There is a unit that kinda does this called GasJack from Compressco.  The compressor side doen't seam to make enough air though when I looked at the curves.

RE: Self Supercharging engine

2
I think we also need to account for swept volume.  In a conventional engine, where all 8 cylinders have the same swept volume (and are all tied to the same crank), using 4 cylinders won't give you any additional air per cylinder, if they feed the other 4 cylinders.  To make this work as a supercharger, you would need the 4 "compressor" cylinders to have a larger swept volume per cylinder than the 4 that are used for making power.  Then you would have a higher than atmospheric pressure in the power cylinders prior to their compression stroke.

Certainly not impossible, but not terribly practical, and absolutely not going to be allowed by any racing sactioning body in a "limited" class.

-Tony Staples
www.tscombustion.com

RE: Self Supercharging engine

It could be done, no special cam required, reed and or check valves. If i were the sanctioning body i would allow it no problem, convert as many cylinders as you like to supercharging so long as they all count towards the displacement limit. that being the case i suspect it would be a net loser. but i could be wrong ?

RE: Self Supercharging engine

It was done about 100 years ago on some early 20th century French racing cars. I forget the details.

It is a supercharger, so it would be illegal. A supercharger is a device to compress the inlet charge before it enters the cylinder.

Regards

eng-tips, by professional engineers for professional engineers
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RE: Self Supercharging engine

(OP)
Thanks so far guys. All very good comments. Anyone else want to chime in?

RE: Self Supercharging engine

Tstaples- Thanks, that was what I was trying to realize in the back of my head, I couldn't express it though. Star for ya!

RE: Self Supercharging engine

There has been rumor of people routing air through the bell housing to get some boost.  The rumor said the Differential pressure was measurable.  Put a couple holes into the top and route the positve pressure one to the air cleaner.  A dividing plate between them may even help guide the air out bell housing.

I know were not about rumors here, but I thought the theory was interesting anyway.

RE: Self Supercharging engine

Sure just a very inefficient centrifugal blower.

RE: Self Supercharging engine

I think a reed valve compressor is a 2 stroke, so equal cylinders would pump about twice as much air as the 4 stroke consumes thereby giving near 15# boost, depending on the VEs of both sides.

Regards

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Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.

RE: Self Supercharging engine

re the bellhousing blower - you might well get a bigger power boost by evacuating the bellhousing!

Cheers

Greg Locock

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RE: Self Supercharging engine

Pat,

you are absolutely correct.  I was assuming one stroke per each.  If you added the reed valves, then you could get boost by using two pumps of the "compressor" cylinder, for each four stroke cycle.  Then the problem becomes one of how to route air. To me, the smart option would be to use the "exhaust" valves as inlets for the compressor cylinders, letting the compressed air into the common intake via the normally "intake" valves.

Still, frightfull to implement, but fun to toss the idea around.

-Tony Staples
www.tscombustion.com

RE: Self Supercharging engine

Somewhat related:

While in its death throes, Triumph Motorcycles (the old one) came up with a piston having two skirts, the second much larger and attached at the bottom to the first.  The engine was a twin, and the cylinders supercharged each other.  There were, of course, two concentric cylinder surfaces for each cylinder, too.  Given the extra complexity, the difficulty of making annular cylinders and annular pistons, and the difficulty of cooling and lubricating the combustion cylinder's walls, the idea probably didn't stand a chance, but it was a clever thing to have been exploring, in a company that was _not_ in dire financial straits.  Given the company's business situation, I thought it was an irresponsible distraction, or maybe a last gasp.

Mike Halloran
Pembroke Pines, FL, USA

RE: Self Supercharging engine


Have a Google for:
Comprex Pressure-wave supercharger
United States Patent 5799641

Bill

RE: Self Supercharging engine

Re: bellhousing supercharger.
In Smokey's three book series there is a brief description of a bellhousing supercharger. He said he welded fittings onto the housing, then filled it with expandable foam. When the engine was started it cleared a passage through the foam, and once the outlet was cleared of foam he claimed it produced positive pressure. My memory is foggy on how much it was able to produce or what sort of difference it made.

Thanks,
Jack

RE: Self Supercharging engine

Smokey claimed 22psi. dead headed at 6,000rpm. Did it make a difference? Look at the lap times of the 1962 Daytona 500 winner. Nobody else was even close.------Phil

RE: Self Supercharging engine


Static pressure -- no flow (?)

Bill

RE: Self Supercharging engine

22 psi from a flywheel at 6000 rpm. Just give it a bit more of a rev and it could pump up tyres.

Regards

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RE: Self Supercharging engine

22 inches of water maybe ?

RE: Self Supercharging engine

The weight of 22 gnats whiskers per sq metre maybe, unless it has a very special shape to the clutch pressure plate and / or flywheel.

Regards

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RE: Self Supercharging engine

And don't forget to remove the transmission,  it's blocking the inlet.

RE: Self Supercharging engine

My copy of Smokey's book states:

"Now I have everything clean inside and stick a bottle of urethane at a hole and press the button, everything inside gets full of foam. Let it harden. Now crank engine up and cut a path for the rotating parts. Then...opened the entrance and exit areas up with a knife, then cut room for throwout bearing and fork. Then run engine up to 7000 rpm AND FIND OUT YOU GET 10 PSI OF PRESSURE, AND ARE PUMPING 800 CFM WITH NO PARASITIC LOSSES."

800CFM at 10 psi?????  Jeez, that's a lot of air.  I don't buy it.  Unless he left out the part about building the engine with a special turbine shaped  . . ..  Aw, never mind.

-Tony Staples
www.tscombustion.com

RE: Self Supercharging engine

I like the part about "no parasitic losses"... the turbocharger and supercharger manufacturers will definitely want to keep this one suppressed.
With all that foam insulation, I guess you'll need an adiabatic clutch & t/o bearing that can really "take the heat"!

RE: Self Supercharging engine

Heat is not a problem.  When the clutch gets warm, the urethane will melt and/or burn away.



Mike Halloran
Pembroke Pines, FL, USA

RE: Self Supercharging engine

And as it burns, it will produce cyanide gas, thereby eliminating competition that is following closely, that is so long as the firewall and floorboards are gas leak proof.

Regards

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RE: Self Supercharging engine


I think I can understand (maybe) the use of the flywheel ring gear teeth as a pumping mechanism. After all, a lot of current electric fuel pumps do just about the same thing - peripheral toothed wheels rotated at high speed.

To get these things to work with any sort of efficiency, you have to use very fine tolerances and have the 'turbine' shaft running at quite high speed to generate the sort of peripheral speeds where the pump works best.

I can imagine the foam providing these sort of close-fit conditions, but as to how wide a speed range that would provide a useful boost....?????

What happens when the crank end float gets so that the foam is worn away from the flywheel.....efficiency drops/dissappears.

Bill

RE: Self Supercharging engine

Haven't been on here for a bit.

I have been involved with a project that uses crankcase pressure as a source of forced induction. The mixture is pulled into the crankcase as the piston rises and expelled as the piston drops, airflow is controlled by a rotary valve running at crank speed, so you get two displacements per power stroke. This feeds a plenumn which feeds the inlet to the cylinder. In terms of psi boost the figures were low compared to more traditional forced inductions, but required very little in the way of extra moving parts, and the figures were obviously higher than a NA engine. The fuel was mixed 50:1 with stroker oil for lubrication of the bearings and rotary valve. The majority of the engines built were only small capacity for use in an Ecomarathon car, but a larger engine was still born when the UK motorcycle speedway authority got wind of it and banned the concept before the prototype was finished, let alone running. Without a market the research ended. Only works if the engine is a single or has seperate crankcases.

RE: Self Supercharging engine


Hmmm.....isn't that just a traditional 2-stroke ?

Bill

RE: Self Supercharging engine

No, because its a four stroke that uses crankcase pressure to force the inlet, hence the comment of two displacements per power stroke. Above the piston everything is as a four stroke, with the overhead cam drive also turning the rotary valve for the crankcase, no transfer ports, and non of the two stroke inefficiency.

RE: Self Supercharging engine

So you are gaining positive displacement supercharging via internal design mods instead of an external device.  What are the pluses & minuses relative to conventional positive displacment supercharging?  (in terms of cost, efficiency, flexibility (i.e. control of pressure ratio), & oil fouling/smoke/particulates)?

RE: Self Supercharging engine


 Many large bore 2-stroke, x-head,slow speed  Marine diesel engines use under piston compression to supercharge the air manifold. This concept has been around for many years. The drawbacks are large accumulation of sludge in the air manifolds over time and danger of fires in this area.

RE: Self Supercharging engine

Mike Halloran,

The Triumph project you mentioned was a two stroke 500cc twin called the Norton Wulf. (Norton Viliiers Triumph by then, no matter).

The concept was to develop a two stroke engine with low emissions. Because the crankcase was sealed with regard to the combustion chambers, it could be lubricated by pump and return tank as a 4 stroke, rather than by the usual total loss / burn it and blow it out system.

It looked fairly conventional from the outside with carbs on the rear of the two cylinders. I recall it looked like a cross between an Ariel Square four and a Suzuki twin. However, the intakes were crossed over, so that a mixture adjustment on the left cylinder was made at the right hand carb.

There may be some merit in the concept even now. Like all the other good ideas from that factory, such as the Bandit and Fury modular bike engines, they were sadly strangled at birth due to the foolish refusal of the mangement to reinvest in the business in the face of new and rapidly emerging technology from the far east.

The prominent engine designer for Norton at the time was Bernard Hooper, who, I understand, is still experimenting with this type of engine.

I read all this almost as it happened, at school in the early 1970s from my smuggled in copies of Motorcycle Mechanics, whilst supposedly reading Shakespeare in English literature lessons. Consequently, I know a little about British bikes but I still don't know my Puck from my Bottom.

RE: Self Supercharging engine


PEW - not knowing yer Puck from yer botteom.....could be nasty if you ever have to explain any pains to your doctor.

Bill

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