At the ILA show in Berlin this week, a German company called Bauhaus Luftfahrt showed off an intriguing new aircraft engine that combines piston engines with a conventional turbofan design in what it calls a composite cycle engine. A long-term concept powerplant, the company estimates such an engine could be ready for introduction in 2050.
The concept incorporates piston engines into the core of a turbofan engine and the increased thermal efficiency of the piston engine enables higher peak pressures and temperatures within the core engine. With a fan diameter of 9.5 feet and a total length of 19.3 feet, the engine will derive its power from a 20-cylinder piston engine. Despite a weight increase of nearly 30 percent over conventional systems—the model shown weighs in at 2.5 tons—a reduction in fuel burn of 50 percent is possible, the company claims.
The concept resembles a conventional turbofan architecture at first glance. Consequently, the lightweight turbo components provide engine thrust, pressurize the piston system and extract the energy from the core-engine flow. The piston system tops the turbine engine cycle at pressures and temperatures unseen in existing turbofan engines. In this design, the piston system runs mechanically independently from the turbo shafts and can be placed freely within the engine core. At the same time, the low-pressure turbine provides power for the fan only and becomes smaller.
This novel concept makes it possible to achieve peak pressure ratios of more than 300 to 1, compared to about 60 to 1 for advanced turbofan engines. This reduces fuel consumption of the aircraft by 15 percent, allowing it to meet or exceed engine efficiency targets for the year 2035. The engine core size remains constant compared to a turbofan. NOxemissions are reduced by 10 percent, compared to advanced lean-burn combustion technology.
