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Concept: Compact Two-Cycle, Co-generating Piston-Driven Turbine to Deliver 60+% Efficiency

One implementation of the two-cycle Reinhardt Turbine. Click to enlarge.

A German company, vv-tec GmbH, is developing a compact piston-driven turbine—the Reinhardt Turbine, named after its inventor—that it says is a two-cycle (gas and steam) thermodynamic process machine that can be built with conventional components and can achieve efficiency of at least 60%.

The engine components are contained within a sphere. The first cycle is a “conventional” combustion engine process using a combustible fuel with the crankless (i.e., free) pistons converting their linear motion to rotary via a sinus disc. Waste heat is transferred within the sphere to create steam in a closed process that then drives the second cycle and set of pistons (built around the first set), using a similar sinus disc.

About the Inventor
Gert Reinhardt was trained as a Mathematician at Dortmund University. He worked for the Korf Steel company in Saudi Arabia as head of IT. In 1983, he founded a document management software company called SER AG.
SER went public on the Neuer Markt in 1997 and achieved a market cap of €1.5 billion. SER’ document imaging product ITA had the largest volume of any document management system in the world.
Gert also designed a storage jukebox that was used by many of the largest companies in Europe.

The engine is classified as a turbine, says Jim Andrews, vv-tec’s President, because the use of the sinus discs make the engine into an impulse turbine. The sinus discs also helps the efficiency of the generator—30 kW of engine power will run a 30 kW generator. “With a traditional crank spinning from the center, you need a higher rated engine power than generator power. We get the benefit of spinning from the outside…precession,” Andrews says. Another benefit of the sinus disc is that it eliminates the need to crank the piston, thus making a true floating piston.

The gas process is no different than the Otto cycle. Fuel and air are compressed, then combusted. Any combustible fuel can work in the Reinhardt Turbine, the limiting factor is emissions control.

By cogenerating power from gas and steam, vv-tec claims, the Reinhardt Turbine achieves efficiency of at least 60%: 40% from the gas cycle, and 20% from the steam cycle. Andrews says that vv-tec has efficiency gains possible in the steam cycle up to 30% through miniaturization and heat transfer improvements in the form of a new patented piston-in-piston technology.

Without co-generation—i.e., without the steam cycle—the engine would run at 40% efficiency with a high power density of 1.5 kW kg-1. With the current level of co-generation, a 100 kW Reinhardt Turbine would be the size of a beach ball and weigh about 50 kg, according to Andrews.

In addition to optimization through miniaturization and heat transfer improvements, other potential refinements include:

  • Using more 1-stroke pistons, aligned closely together through the use of miniaturization, to deliver more constant heat and pressure than the first generation machine.

  • Since the Reinhardt Turbine is used only to create electricity, it runs at a constant speed like a conventional turbine but with efficient closed combustion chambers. Future Reinhardt Turbines will be able to vary the stroke-to-bore ratio from 1 to 1 in the first generation to 3 to 1 in the future.

Two potential configuration of a Reinhardt Turbine. Left: a 14-cylinder star configuration, with the sinus discs at each end. Right: a 3-cylinder module of a 9-cylinder turbine using an external sinus disc. Click to enlarge.

In a sphere the number of simultaneously used discs can vary. Together with the properties of symmetry or asymmetry, the arrangement of pistons and cylinders within a sphere can be realized in different ways according to its application. Moreover, it is easy in this context to switch on or off single pistons to reduce torque, increasing the efficiency of the engine.

The engine is designed to generate power only, in applications such as a genset for an extended range electric vehicle, or in distributed power generation. Parallel to the development of the turbine, vv-tec is planning the development of smaller high-performance electric generators.

Cogeneration schemes are well-established in advanced power plants, where thermal efficiencies can reach up to 80%—but at a very high cost. The Reinhardt Turbine is designed to be compact, cost-effective and easy to manufacture. Andrews estimates that the manufactured cost per kW will be less than $10, so a 30 kW engine would cost around $300. “Add in a few kWh of lead-acid batteries and you have a cheap and efficient advanced powertrain.

The company has videos on its website of three prototypes demonstrating the use of the sinus disc, the engine perfectly balanced with a two-stroke arrangement, and co-generation. vv-tec expects to be operating an external sinus disc prototype shortly.




I would not call it a turbine, but rather a free piston engine. It has a unique heat recovery scheme, but they would need to take it beyond a concept to see.


A 60% efficient very light weight genset would be ideal for all PHEVs (and series HEVs) if it works and last long enough.

Somebody in India has designed a 24 lbs, 24 hp very light weight diesel. Any more details?


Beach ball? How big of a beach ball? I've seen some big ones (huge one in my garage).

Bold claim of 40% efficiency on the gas cycle when most ICEs run ~28% on Otto cycle. The good news is that firctional losses should be vastly reduced with this design.

Pretty brilliant the way they incorporated the heat recovery IMO, though it does limit RPM to whatever steam expansion can handle.


Fisker uses the 2 liter turbo from the Solstice to generate power. I thought this was overkill, until I remembered that direct injected turbos can create good power at low RPMs. Different motive forces for range extenders will emerge.

Will S

...the limiting factor is emissions control.

This is the only mention of emissions. Too early to expect much, or are there indicators that show this may be a risk area?




Large combined cycle power (gas and steam turbine) with a power rating of 400 MW do not even reach efficiencies of 60%.


The TMA guys have a brayton/rankine unit that could be used for a range extender. Claimed efficiencies are not has high, but it is suppose to actually work.



1. The power transmission isn't new (axial cam disk).
2. It's not cogeneration as you don't use the heat to heat i.e. a room, it's a combined cycle (like CCGT). I think the best efficiency reached so far is almost 60%.
3. "where thermal efficiencies can reach up to 80%"
- It's not thermal efficiency, it's overall efficiency.
4. In one of the animations they say the temperature reached is 2000°C. The same animation claims a thermal efficiency of 90% to 95%. Even if you were able to expand down to, i.e., room temperature, you'd still only reach a Carnot efficiency of round about 87%.
So, I don't quite believe their numbers, but anyway interesting concept.


Hardly Vaporware - I call it Hardware, too much of it.
This thing has a part-count problem that will ultimately lead to its demise.


JosephT wrote:

"Large combined cycle power (gas and steam turbine) with a power rating of 400 MW do not even reach efficiencies of 60%."


Siemens recently installed a plant that was described in the IEEE which gets 60% efficiency.

Roger Pham

Mathematicians need a glimpse of reality also. A heavy-duty turbocharged diesel engine is the most efficient internal combustion engine on land at the moment, having BTE of 42-45%. Cummins plan to use an intricate Rankine-cycle heat recovery system to up its efficiency to 50%. Look in:


A heat engine with the size of a beach ball with a claimed BTE of 60% is simply absurd. There is nothing new about an axial piston device, nor about the method of combustion, nor about heat recovery inherent in the so-called "Reinhardt turbine." Real engines suffer from mechanical losses that are usually ignored in the calculation of an imaginary or theoretical engine.

Large combined-cycle power plants achieving 60% BTE due to their low frictional and thermal losses inherent in the very large turbines...plus a very complicated heat-recovery mechanism including multiple re-heating stages for the steam turbines...not possible in a smaller automobile-size application.


Their claim of 60% efficiency is certainly optimistic, but I found the idea of having an integrated steam recovery and ice interesting, usually the price of adding a steam recovery engine makes the HP/Kg dropped but if it is integrated the HP/Kg can still be high. Also if you use a centrigugal heat exchanger like the the cyclonepower one you could clean the exhaust of a diesel while you recover the heat then you could get rid of the catalyst and exhaust treatment. Might worth having a closer look.


Their insistance on calling this a turbine is weird.
It only gets worse from there.
This gives vaporware a bad name.


1.ICE efficiency in real life conditions is lower than 20%.
2.Capstone turbine efficiency and any other gas/liquid turbine efficiency less than 30%.
3.The existing "wet" or "Top hat" gas/liquid turbine efficiency 40%. CHP (gas/steam turbines with heat oftake) el. efficiency less than 50%.
4.At large power plants superheated steam cycle and condensing mode with no heat oftake for other purpose at higher than 700 C could achieve 60% (Siemens).
They claim high operation temperatures and are able to achieve best electrical efficiency in the world. It would be application for Nobel Prize.


P.S. In case 2000 C combustion temperature NOX will big problem.


Count me with the skeptics.  The figures claimed for this are completely out of line with combustion engines of any kind, compounded and bottoming-cycled or not.  I'll believe it when I see the BSFC figures from a dynamometer test of a sample, and not before.


lets be generous and give any ICE a 40% efficiency, leaving 60% heat (including frictional) to work with.
Now the task is to garner 33% efficiency (not such an absurd number) from the remainder .
I'd be looking at a sphere for best thermal retention as shown.

"though it does limit RPM to whatever steam expansion can handle."
Not sure about that statement but the three chamber
sinusoid is relatively slow as a complete rotation is utilised.
"Since the Reinhardt Turbine is used only to create electricity, it runs at a constant speed like a conventional turbine but with efficient closed combustion chambers."
While no rpm is given, efficient closed combustion chambers.", "40% from the gas cycle"
Indicates a high efficiency here - no idea how they manage that and from a twostroke? but at constant rpm, It is conceivable.
The other clue that follows my reading is " Future Reinhardt Turbines will be able to vary the stroke-to-bore ratio from1 to 1 in the first generation to 3 to 1 in the future."

This longer stroke ratio would allow a longer time to extract the higher efficiencies from both sides as would be required. Again no understanding how that may happen, but it sounds consistent.

I've thought for some time that the crower cycle could change the game by utilizing reject heat, but there may?could be some contamination issues.

one thing is clear that ICE as we know it is never going past 40*% and that 'fiddling around the edges' is not good enough for the new challenges we need to meet.

"We will not solve the old questions with the same thinking that created them" or something like that.


33% efficiency is pretty good for a steam turbine.  For a small piston unit, it's very unrealistic.


Siemens recently installed a plant that was described in the IEEE which gets 60% efficiency.

Wrong answer. Proof and link it and don't just have a big mouth about it!

By the way, Siemens does not even claim 60% efficiency on its website:

Besides, even if 60% efficiency would have already been reached and topped by Siemens (big if), that doesn't change my point that if an extremely large, complex machine has difficulties to reach this point, a smaller machine will even have more difficulties to reach it. (Thermal losses per power unit, fluidic and mechanical friction per power unit drop with engine size.)

33% efficiency is pretty good for a steam turbine. For a small piston unit, it's very unrealistic.
According to the Argonne Labs the Toyota Prius (first generation) generated a peak efficiency of 37%:

A small piston engine does reach much higher peak temperatures than a steam turbine and thus can be capable to reach a higher peak efficiency. Well, at least as long the steam turbine is not part of combined cycle power plant with a gas turbine running at higher temperatures.

Ernie Rogers

It is possible to reach very good efficiency in a piston engine while keeping cylinder temperature below the NOx formation range. I am modeling a somewhat conventional engine that achieves 60% efficiency with a peak cylinder temperature of 2,000 deg K (1,727 Celcius). The thermodynamic requirement to reach this efficiency in one stage is a compression ratio of 40. At the end of the piston stroke, the gas temperature is only 450 C, so there is very little energy left to extract.


BMW has integrated a combined cycle engine in a car:
and claimed to increase efficiency by 15%.
(This, for example, would lead to an efficiency increase from 33% to 37%.)

Regardless: Assuming plug-in hybrids will ever pick up, high power density will probably be more important than engine efficiency. At least, as long as the gas engine will be utilized rarely (since the gas engine still has to be carried around all the time and its weight does decrease the overall efficiency of the vehicle.)


Side note:

Gert Reinhardt the inventor of this engine certainly appears to be crafty sales person:

The stock price of the company SER AG he founded 1997 went from 1 Euro up to 71 Euro and is now back to 0.01 Euro. Obviously he got out long before the stock price crumbled...


I was nosing around You Tube and came across the Hale engine. I thought it was a clever design.



globi:  I was referring to small steam engines, not ICEs.

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