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Concept: New Piston/Scavenging Loop Engine for Performance Boost

A 4-stroke cycle with the Creel Loop engine. Click to enlarge.

A small engine company, Creel Loop LLC, based in Louisiana, is working with a new patented piston design that, in combination with a scavenging loop engine design, functions essentially as a low-cost, naturally-aspirated supercharger to enhance the overall performance of combustion by increasing power output, reducing engine wear, and by reducing the level of unwanted emissions.

In the Creel design, the piston and air diaphragm of the scavenging pump assembly are co-linearly aligned and rigidly connected, using an air diaphragm connecting member that passes through the crankcase. As the piston compresses a loaded air-fuel mixture in the combustion chamber, it causes the air diaphragm to simultaneously draw an air-fuel mixture into the air cylinder without interfering with or relying on the rotation of the crankshaft.


Prototype of the Creel piston with an inset of the finished version. Click to enlarge.

When the loaded mixture ignites, the piston reciprocally retracts from the combustion chamber, causing the air diaphragm to supply the new mixture to the combustion chamber through a routing assembly that routes the new mixture from the air cylinder directly to the combustion chamber, without exposing the new mixture to engine lubricating-oil contained in the crankcase and oil pan.

Creel started by focusing on two-stroke applications, but has shifted to a single-cylinder four-stroke. The company is currently building and testing a 6.5 hp engine. They anticipate delivering better low-end torque and improved fuel economy compared to a conventional engine of the same size.

The company is looking at promoting a two-cylinder application of its engine in a hybrid system.




Another interesting experiment in the field of mechanical engineering; it's great to see all this creativity; however, there may be no market for the device. The move now is to battery powered, electronic controlled, electric motor drive-lines. Perhaps the group's energy could be better used to develop more efficient devices in the field of BEVs, i.e., the development of even more efficient electric motors, better re gen energy recovery, a more efficient a/c system, etc. With the advent of electric cars, wearing components become a smaller part of the package and repair becomes a black box replacement procedure for most.

Justin VP

Interesting piston design they have. I wonder how the efficiency of their system compares to turbo-charging given the added complexity, weight and drag that comes from an extra set of piston rings and another cylinder wall.

Motorcycle/scooter engines seem like they could be a good potential application due to the fact that turbo-charging doesn't adapt that well to bikes. Maybe also recreational marine engines, which are notoriously inefficient.


there will be a need for a small charge sustaining genset in some hybrids.. but can it compete with a small turbocharger?.. no need to worry about lag in a genset.

Helen K

The ICE is not dead with the BEV.

For ages and ages the batteries will be very expensive. This means that you can for yourself decide how big a battery you want. Most will want a battery pack that covers the daily commute. This will reduce the gas usage by 90%. For those weekend trips you need an ICE that provides enough power to keep you going at 100 kph. This would be an ICE in the range of 10 kW. This ICE should be light, fuel efficient and cheap.

Rafael Seidl

@ Lad -

we all know you're a fan of electric propulsion for cars, but did you notice that the company is building a 6.5hp engine? The target market is obviously not cars.

Even so, the design strikes me as inelegant: first, the engine has to be mounted horizontally because of the oil in the carter. That means you want to keep the gap in the oil sweep ring away from the bottom by securing it against rotation and, you want the crankshaft to rotate in the other direction to ensure adequate oiling when lateral forces on the piston are at their highest.

Second, the boost pressure can't be very high with all that dead volume in the compressor piston - the intake reed valve needs to be parallel to the piston crown.

Third, the reciprocating mass is greatly increased, increasing mechanical stresses on the cranktrain an journal bearings as well as free inertial forces and/or moments.

Fourth, the additional set of piston rings creates additional friction. They might as well have eliminated the connrod with a scotch yoke.

Fifth, the illustration implies the pre-compressed air is not intercooled as it passes through the feeder manifold.


I don't like it too much though I think some of Rafael's concerns are off-base. Quickly: the first engine is a proof of concept so its power has little to do with the target market, many things one might add to an engine to make more power will increase friction, horizontally opposed pistons are a very mature technology so no problems there, intercooling isn't that helpful for positive displacement superchargers.

The main thing I don't like about it is that it makes relatively poor use of the extra cost and mass for cylinder, piston, etc. Once you've paid for those things, why not go ahead and add a cylinder head and use the opposing cylinder to make power: probably more than it adds as a supercharger.


Boy! don't know what gave ya that idea(ha).
But. I will confess that you are right. However, I do like creative engineering, no matter what field, I especially like to see the workings of good MEs. As a fact, I love ICE race cars and I'm in the middle of developing an old rusty turbo modified Datsun 240Z and my ability to drive it.

John Taylor

Several things ...
First, the piston wall can be reduced as it is no longer required to keep the piston straight in the cylinder.
Second, the air pump head needs to be larger than the cylinder, so that a larger air volume is involved in actual combustion.
Third, fuel injection seems to be a “must” for this engine design to work efficiently.
Fourth, the use and placement of flapper valves is hopefully just a schematic representation, and that the design has compressor style valves that function.

But ... it might be a workable, and more efficient engine.


I'm not an engineer, but isn't the advantage of turbocharging (unlike mechanical supercharging) that it captures some of the latent energy otherwise lost in the exhaust? Why would this supercharged design have greater thermal efficiency than a well-designed, naturally-aspirated engine, let alone a turbo-boosted design? Also, wouldn't the extra reciprocating mass limit RPM, making for a heavy engine for its power? It makes for a mechanically simpler supercharger, perhaps, but I don't see why it should be any more efficient than conventional designs.


I'm glad to see someone is working on improving the ICE, they are not going away any time soon. With alternative fuels like hydrogen, this could be a real win, because it does not provide as much power as gasoline. So, I cheer them on, and hope the can start making better engines for vehicles also.


By capturing energy from the exhaust gases a turbo increases back pressure, so it is not "free" it has losses just like a supercharger. They are just in a different form.


I don't know where they want to go with this, there is so many things much more promising than this that they could explore, like free piston engine for series HEV, clean 2 stroke engine, non sinusoidal engine for more complete combustion, variable compression ratio, low friction engine with no lateral component, HHCI, multijet diesel, well try to overcome the limitations of today engine instead of thing that useless

Toppa Tom

You are right on Nick. However it does look like the 4 stroke version has two air pump compression strokes for one intake stroke to achieve actual supercharging. But then all the piping volume will reduce the supercharging quite a bit. Why not just admit this will compete with stationary power plants.


It looks like a copy in some respects to pattakons designs.
which some of you have not liked.


You could do a 4 cylinder boxer engine using a scottish yoke and use stock pistons. You might not be able to patent it, but it should be less exotic.

Roger Pham

I have to agree with Rafael about the "in-elegance" in this concept!

This design is no more than a supercharged engine using a piston compressor. All supercharged engines, whether pressurized by a scroll compressor, twin-screw compressor, or centrifugal compressor, etc. suffer from inefficiency due to the lack of proper expansion for the exhaust gas while having to invest more precious engine power into driving the compressor. At least, in a belt-driven and clutch-connected compressor, you have the option of disengage the compressor when boost is not needed, hence reducing friction on the engine. Here, you don't have that option.

By contrast, a turbo-supercharged engine does not have to use engine power to power the compressor, but this power is harnessed from the residual pressure of the xhaust gas. Excess power from the exhaust turbine can also be added back to the engine crankshaft, or driving an electrical generator, to accomplish turbo-compounding, which further increase engine efficiency.

A centrifugal compressor is much more compact and lighter, and having much less friction than a piston compressor. A turbo-supercharger is very compact and very light with respect to the amount of airmass flowing thru it, and that's why it's the preferred method of engine supercharging.


It's basically a 4 cycle engine that pumps the amount of air of a 2 cycle engine.

With the same size and not much more complexity (e.g. turbo) it can almost double the power at the same rpm.

If it was used in a plug in hybrid as an 'emergency-engine', there could be some merits to this concept - since low weight, low volume and little complexity is more important than maximum efficiency and high dynamic range.
Besides, increasing BMEP does generally also increase efficiency.

Reminds me of a crankcase-ventilated 2-stroke.


You could make the compresser piston larger and have true supercharging.

You could also put a small chamber on the intake pipe with an additional check valve to get a double air charge for every intake stroke.


The main problem I have with this is the need for a major intercooler. Any charge coming from under the piston is going to be hot and hot is not good for a cylinder charge.


You could make the compresser piston larger and have true supercharging.

No, you already have TRUE supercharging.
The piston on the left pumps twice, while the piston on the right only pumps once per full cycle.

The main problem I have with this is the need for a major intercooler.
I don't see why they couldn't integrate an intercooler.


You could make the compresser piston larger and have true supercharging.

No, you already have TRUE supercharging.
The piston on the left pumps twice, while the piston on the right only pumps once per full cycle.

The main problem I have with this is the need for a major intercooler.
I don't see why they couldn't integrate an intercooler.

Rafael Seidl

@ Nick -

supercharging can improve fuel economy a little if it is used to reduce engine displacement and hence, weight and internal friction (aka downsizing).

Mercedes has been doing this for a while with their Kompressor models, though advances in turbo technology make it the more attractive approach if the primary objective is improved fuel economy.

globi is correct, there are two piston strokes per power stroke, that would give it decent supercharging.

An inter-cooler for a high performance engine would help but not a necessity for a low compression version.


This is the basic operation of two strokes and it would
make more sense to just remove the valves and have it
operate as a 2 stroke with oil in the crankcase instead
of in the gas. Check out the Miller cycle engine it
uses a supercharger and it basically keeps the intake
valve open and it force the air into the cyclinder until
the SC hits its limit then it closes and let's the
piston compress the air the rest of the way. Since a lot
of energy in a engine is lost to the crank having to
push against the air charge. Letting a turbo or SC do
the compressing at least until it reaches it's limit
does save a bit of power. Of course we should be taking
the gasoline and splitting it and using the hydrogen
as fuel and the carbon to build the cars and if we reduce the weight then we increase the efficency. It all
comes down to power to weight ratio and that will save
more fuel. A carbon fiber unibody car, aluminum engine
and of course smaller will save alot of pollution and
wasted fuel. OF course we all need to get used to going
much slower then we do and cruising at 80-90 mph on the
highway get's us to our destination faster it also gets
us to the gas station faster!! Hence more pollution if
we slowed down to say 65 tops (for all vehicles) the
fuel consumption would drop as well as wear and tear and
of course the number of deaths!!

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