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Concept Engine: Intermeshing Differential Rotors

The basic element of the IDR engine is two intermeshing rotors. Click to enlarge.

A South African inventor has developed a new engine concept—the Intermeshing Differential Rotors (IDR) engine—intended to provide a better power-to-mass ratio, improved efficiency, reduced manufacturing cost and durability than current engines. The company commercializing the concept, IDR-Technology, introduced the IDR engine at the 2008 SAE World Congress last month in Detroit, where it won an AEI Tech Award.

The engine is based on two rotors that intermesh but turn at different speeds and alter the speed ratio between them. The rotors alternately drive the engine, with the combustion chamber forming between the intermeshing arms of the two rotors.

The rotor with the biggest leverage on the other rotor will drive the engine or part of a revolution (both rotors will turn). Then the other rotor will have the advantage and turn both rotors.

Combustion occurs every time the rotors exchange angular velocity ratios. The change in roles occurs 12 times per engine revolution—each rotor driving 6 times—producing 12 combustion events. Combustions occur every 30 degrees of outward axle movement, giving IDR technology its high power-to-mass ratio.

The IDR engine has a 3-stage compression and 3-stage expansion cycle. The distance between the two parallel axles of the rotors corresponds to the stroke of a piston engine. The closer they are the greater the “stroke” and the more volume is swept.

The height of the rotors corresponds to the diameter of a piston in a piston engine. The longer the rotors are axially the greater the swept volume will be for a specific axle separation.

High compression ratios of up to 25:1 are possible, and variable intake and exhaust displacement volumes can be created by changing the outer housing shape and position. Multistage compression and expansion cycles can improve efficiencies.

The company, which is filing forpatents on the IDR technology,  is seeking early-stage investment.




Interesting and entertaining. Looks like it combines the seal and "over quench" problems of the Wankle with the uneven wear of a slide valve engine. The irregular motion looks worse than in a recip. Power to weight does not appear so hot either.
Otherwise it looks great.


I walked by this display at SAE. I'm not an engine guy, but I was impressed by the mechanical give and take dance that the rotors do.

I am concerned, though, that wear or small variations on the red and blue disks with the curlicues and the pins that mate with them will be amplified in the rotor positions at any given moment.


Looks like it was created by a mad watch maker! Seriously, it would suffer from cooling and seal problems like all rotory engines do.

there is already plenty of rotary design engine like Quasiturbine and RandCam, they all suffer the same issue of wear out problem, seal and cooling of the rotor and leak. The Rancam design look pretty cool on the paper but have been working 8 years on this concpet and still nothing, each time a start up lauanch a new rotary engine they end up in selling it for pumping or steam engine.

So this design as smart as it can be, isn't more likely to make it through than other rotary designs.

richard schumacher

Similar things have been re-invented for decades. For a survey of past efforts see

They sometimes make acceptable pumps but usually terrible engines.

Henry Gibson

Delightful design. I hope that it is built and tested.
I have a great idea for a clutch system to couple it with wheels.

Capstone turbine has an oil-free turbine design that might be able to be miniaturized to about 15 HP and made more efficient for installing into a plug-in-hybrid car. Then modify a Tesla for a turbine so that you can have high torque and high peak power and indefinate range and the ability to cleanly burn biodiesel or diesel in a turbine that will run constantly for 8000 hours between air filters.

It would not be hard to have a computer control of the burners that would allow any liquid fuel to be burnt in the same machine.

I guess that the patents on the NOAX Centaur free piston engine will prevent for a very few years more this mechanically simple but electronically complex machine from being used even in the INNAS hydraulic hybrid. But it is the only compression ignition machine that could be used on pure methane (Propane Butane Hydrogen).

The OPOC engine retains competative features for series hybrids, and should be recommended for all of them....HG...


I'm sure I saw something like this the other day on the discovery channel... I kinda remember that besides the increased engine efficiency, it also led to a smaller and thus lighter engine, which meant it also provided for a better gas mileage...

Neilen Marais

Quite intereseting. Regarding the typical problems facing rotary engines, it seems that this design does at least address 2.

1) Cooling should not be so bad, since the rotor blades are passive (i.e. not involved in combustion) > 50% of the time

2) The lack of eccentric movements may ease the seal problems.

Well, I say this as a lay person, but it does actually seem better than e.g. Wankel engines in those regards... Any real mechanical engineers, feel free to pitch in :)

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