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Concept: AET Reaches Final Development Stage of OX2 Barrel Engine

Exploded view of the OX2 Engine. Click to enlarge.

Advanced Engine Technologies Inc. says it has reached the final development stage of its OX2 rotary engine, achieving a performance objective of more than 300 lb-ft (407 N·m) of torque along with 46 hp (34 kW) at an approximate operating speed of 760 rpm.

The OX2 engine was conceived in Australia by inventor Steve Manthey. The engine is an 8-cylinder barrel configuration, using a stationary head and cam plate, and rotating cylinder block and piston plates. Each cylinder fires twice per revolution and two cylinders fire simultaneously, resulting in four times the output per revolution of a conventional four-stroke engine at the same displacement. The engine can be adapted to run any combustible gas or liquid as fuel.

OX2 in a test rig. Click to enlarge.

Advanced Engine Technologies was incorporated in 1996 to commercialize the OX2, with automotive racing pioneer Carroll Shelby on its Board of Directors and involved in the engine development.

With its expected higher power-to-weight ratio, multi-fuel capacity and anticipated low emissions and fuel efficiency, the OX2 is initially targeted at the commercial and industrial generator markets. Additional future applications may include marine, light-duty farm and construction equipment, light aircraft, and the hybrid electric vehicle market. However, the near term focus remains electrical generator applications.

The OX2 engine achieves considerable torque at all stages through its operating range. Consequently, in most engine applications there would be no need for the engine to operate at revs higher than 2,500 rpm. In some instances, this would eliminate the need for a gearbox and would certainly reduce engine wear.

However, in particular applications, if high engine revs were mandated, the OX2 engine could be adapted accordingly, AET says. A problem with higher revs is that the centrifugal force lifting the pistons from the track increases, requiring engineering modifications to keep the pistons on track.

The current OX2 is a 4-stroke, 1.1-liter engine that is 17 inches in diameter with a length of 13 inches and a total weight of 200 pounds (91 kg) in normally aspirated form. The compact engine weighs 75% less than and is half the size of traditional internal combustion engines.

The major parts of the engine are the housing; cylinder block; top piston plate; lower piston plate; cam track; and drive shaft. The moving parts are the cylinder block; top piston plate; and lower piston plate.

The combustion chambers are only slightly longer than the stroke and pistons need only to be thick enough to house the rings. The OX2 contains no piston skirts and the rings are the only contact point with the bore. In effect, at no time do the pistons touch the bore, and nor are they reliant on it for support. This system eliminates loading on the sides of the combustion chambers.

Engineers continue work on the commercialization package of the OX2 engine/generator with the fabrication of its finish enclosure and footprint. In addition, AET engineers have prototyped a version of the OX2 engine/generator operating in a vertical orientation.

This new vertical footprint reduces the surface footprint by 50%, allowing the majority of the OX2 engine/generator mass to occupy vertical airspace, not floor space. The company expects to demonstrate both its vertical and horizontal units in the future.

On the heels of AET’s new vertical platform development will be a new, smaller and more versatile power electronics unit. Upon failure of its previous power electronics unit, an outside electrical engineering firm was hired to write the new specifications. The company is poised to proceed with the production of two new power electronics units for fitment with the OX2 engine/generators.

The power electronics is the last mile of the OX2 engine/generator development. The OX2 engine/generator currently produces over 30 kW of power, however it is raw power. This new unit will condition the raw power and produce useable power for commercial connectivity and use.

—John Luft, Chief Operating Officer of AET

In addition to the exciting engineering progress made on the OX2 engine/generator, the company has initiated efforts to raise additional capital to fund the OX2’s 30 Kw Generator final development stage.




Weighs 75% less? So a standard 1 liter engine weighs 800lbs? Right....

In general, when you increase cylinder count while maintaining displacement you increase thermal losses and thus decrease overall efficiency. Granted there are significant gains to be had from not needing a gear box and operating at a mere 760rpm.

Hopefully this can evolve into a cheap, efficient, engine for a range extender in a PHEV.


not necessarily greenplease, since there is no crankshaft this is not a typical otto cycle engine. These pistons are very light weight. do they have a running prototype?


Weight has absolutely nothing to do with heat loss. It is a matter of cylinder head surface area exposed to the air inside the combustion chamber.


"more than 300 lb-ft (407 N·m) of torque along with 46 hp (34 kW) at an approximate operating speed of 760 rpm"

"1.1-liter engine that is 17 inches in diameter with a length of 13 inches and a total weight of 200 pounds (91 kg)"

"rotating cylinder block and piston plates"

First, I would not want rotating cylinder block and pistons. Second, 17 inches x 13 inches seems a bit big for 46 HP. Third, it seems to have lots of torque (300 lb-ft) but little horsepower (46 hp). Nice design that gets its power at lower RPM, but they need to do better.


Actually, I've seen a working prototype of this design used for a couple of different applications. It's incredibly efficient and the first use has actually been as a water pump of all things. The same guy has some long standing patents on this design as an engine as well. It will be interesting to see who actually ends up owning the rights to this.



compared to the

1.3liter hayabusa engine

RPM adjusted, the OX2 has a much higher specific power than the engine in the latest hayabusa superbike (which already has an insane specific power). Since there's not much they can do with the combustion, this tells me that the OX2 has very low mechanical/frictional losses.


I have seen opposing piston and cam plate designs where the cylinders and pistons stay put. It is less rotor mass and better response. It looks like a nice design, but reminds me of the rotary airplane engine of the 1920s where the pistons rotated and the plane banked one direction on take off.


it is a 2 stroke which is more efficient, correct green, weight has nothing to do with heat loss but in general pistons are pretty efficient. the bigger problem with Otto is the complexity and weight that additional cylinders cause... not heat loss.

This design may be the engine of the future, there are a bunch of prototypes of these on youtube and on this website in the past. I agree Dave, it will be interesting to see how this innovation is diffused.


Read again. It is a four stroke Otto cycle.

Reasons for inefficiency in a conventional ICE:

1. Heat loss to cylinder head and pistons
2. Mechanical losses (frictional)
3. Pumping losses (air intake/exhaust)
4. Symetrical compression and expansion

Roger Pham

The Ox2 engine developer seems to have a realistic knowledge of the potential limitation of this engine.

First, the sliding valve on the cylinder head will have unavoidable leakage which will be worse proportionally at lower engine speeds, necessitating steady operation at a higher minimum speed. This is similar to the carbon side seals of the Wankel rotary engine.

Second, the centrifugal force on the piston rods will limit top end rpm, thereby limiting maximum power potential. However, due to the fact that this engine rotates at 1/4 the rpm of a crank-slider engine for a given number of piston strokes or cycles, it needs only to rotate at 1500 rpm to be equal to a conventional crank-slider engine (eg. Kawasaki Hayabusa engine) at 6,000 rpm. So, Greenplease, it does not have much higher specific power than the Hayabusa engine, since piston speed and combustion speed will be the limiting factor in higher engine speed, not to mention the high centrifugal force that will increase at the square of the rpm.

So, they are smart in their intended application of this engine as electrical power generator and serial hybrid engine whereby the engine is needeed at only a limited range of operation. That being the case, the engine design reflects high level of ingenuity, simplicity and efficiency. The entire poppet valves and valve train is eliminated, saving a lot of weight, space, cost, and parasite power loss (friction loss). Plus, the entire intake and exhaust manifolds are eliminated, saving more weight and space.

Roger Pham

Another issue raised here is: Why rotate the whole engine block and (subjecting to centrifugal force) instead of just rotating the sinusoidal cam and engine shaft plus flywheel?

The most important reason is that this sinusoidal cam engine turns at only 1/4 the rpm of a conventional crank-slider engine (typical Otto engine). Since E=1/2 MV^2, this means that the rotational energy available to the flywheel would be only 1/16th, necessitating a flywheel 16 times more massive than a comparable engine's flywheel of similar diameter. This would be too heavy, so, rotating the mass of the whole engine block in order to have enough rotational energy to keep the engine running would eliminate the weight of the flywheel that must be 16 times heavier than a typical flywheel.

The second reason to rotate the entire engine block is that to have a simple single port at the engine top instead of complicated poppet valves and valve train etc...


ok, this design is a four stroke (don't know why because it is not needed for balance) but in any case a piston/cylinder assembly has a certain rate of efficiency. Whether you have one or one hundred pistons does not change the efficiency of the piston/cylinder assembly.

I reread you comment and I think you mean that 1 piston with 50cc will be more efficient than 2 with 25cc and this is correct but it misses the point of an ICE which is balance (mechanical, power, torque, etc.) If cylinder efficiency were the most important factor in engine design we would all be driving 1 cylinder cars.

Roger Pham

@Jim and Greenplease,

At a small size of 33 kw power, the efficiency gain from this engine vs. a comparable Otto-cycle engine will be small. Heat loss will likely be higher due to the higher number of pistons, while friction will be less.

However, let's think big, and make the OX2 engine a 3 MW size instead, or 3,000 kw size and even larger, and running Diesel cycle, or better yet, NG or Hydrogen fuel. At this garguantian size, the loss via head valve seal leakage will be minimal, there will still be but 8 pistons per engine, so, heat loss will be comparable with an equivalent Diesel, BUT, the engine can approach 50% thermal efficiency (BTE), vs. 35%-40% BTE of a comparable output but much more expensive gas turbine.

The OX2 engine will need far fewer maintenance work than a Diesel, making it Turbine-reliable, but at much less investment cost and far more efficient than a gas turbine. Plus, the engine can be cycled and shut off and restart without increase in wear as in a gas turbine, in respond to transient electrical demands.

Being similar to a Wankel in that there is always a cool intake side and a hot exhaust side, it can run Hydrogen fuel much better than any poppet-valved piston engine at the present...Hydrogen will be the fuel of the future, synthesized from solar and wind energy...

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