|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.
vv-tec website (extensive material)
Mikalsen R., Roskilly A.P. (2007) A review of free-piston engine history and applications. Applied Thermal Engineering, Volume 27, Issues 14-15, Pages 2339-2352
Frey D.N. et al. (1957) The automotive free-piston-turbine engine (SAE 570051)