The EUREKA E! 2743 KERO project is driving key Federal Aviation Authority (FAA) certification for Wankel rotary engines in general aviation. Swiss project leader Mistral Engines plans to supply a range of such engines for original equipment and retrofitting in all types of light airplanes and helicopters. Advantages include excellent reliability as there are few moving parts, a high power-to-weight ratio, compactness and smooth running compared with conventional piston engines. Moreover, the engine will run on widely available jet fuel. Other potential applications include marine engines as well as light industrial applications such as portable generators, compressors and pumps.
The four-stroke piston engine technology used in the majority of light airplanes involved in general aviation dates back 60 years to the Second World War. So, while designs are well proven, motors require some 70 or 80 moving parts and still run on 100-octane low-leaded (100 LL) avgas fuel that has long been displaced by heavier kerosene-based jet fuel for commercial aircraft. Moreover, 100 LL fuel is mostly limited to North America and Europe; even there it is becoming increasingly scarce - and is soon to be banned completely for environmental reasons.
Mistral Engines therefore saw a major market for a safer, more reliable motor that could be easily adapted to any model of light aircraft and able to run on industry standard jet fuel. The design is based on the Wankel rotary engine pioneered originally in Germany in the 1930s but which emerged at the wrong time. So far, it has only really been developed and commercialised by Japanese car maker Mazda in its RX-8 models and previous models.
"EUREKA labelling enabled us to find the 10 million euro in private equity financing that we needed to see the project safely through to a fully certified product ready for manufacture."
Mistral Engines, Switzerland
Safety and reliability are key factors in aviation. The Wankel engine has a rotor instead of reciprocating pistons, doing away with any need for crankshafts, pistons, valves and springs and reducing the number of moving parts to only two or three very robust ones. With so few moving parts, the engine is extremely reliable and safe. However, the rotary engine is difficult to run in a fuel efficient manner. Recently, the availability of modern automotive electronics has made it possible to overcome timing and injection control complications, resulting in fuel consumption similar to that of piston engines.
Rotary engines for small planes are not completely new. Many amateurs in the USA have adapted car engines for this purpose. It is actually a technology particularly well fitted to aviation applications. “We therefore decided to take the Mazda rotary engine block and to build an aero engine around it that could be retrofitted to all aircraft, explains Claude Geles, one of Mistral Engines co-founders.
“Mounting an engine in an aircraft is a delicate process and very expensive. We also had to design a suitable gearbox. Modern electronics now make it possible to have exact timing for fuel injection and ignition. The resulting engine looks like a turbine; it is not really a turbine but has many of its advantages, including a very low level of vibration, it is light-weight, compact and it is water cooled - making it possible to change power output very quickly without thermally stressing the engine.”
Several partners are involved in the EUREKA project. The Ecole Polytechnique Fédérale de Lausanne (EPFL), where research was funded by the Swiss Innovation Promotion Agency, CTI, is studying the best combustion conditions for the kerosene in terms of combustion-chamber design, injection and ignition. “We are also now developing a special exhaust silencer with the EPFL to limit the noise, using active and passive noise- reduction technologies able to work at very high temperatures,” adds Geles. “This has not been done before.”
The necessary electronic management system was developed with French partner DEM Electronique. The resulting digital engine-control system features full redundancy - essential for aircraft. The heart of the system consists of two separate computers which check each other’s operations continuously. In the unlikely event of one failing, the remaining calculator immediately takes over the entire engine management. Full system redundancy extends to fuel injectors and spark plugs.
Mistral Engines has been collaborating with the Embry-Riddle Aeronautical University in Florida, USA for flight testing. The university will also help in introducing the engine to the US market. “We have had lot of discussions with the FAA and we are certain that our engines can be certified,” says Geles.
"We decided to take the Mazda rotary engine block and build an aero engine around it that could be retrofitted to all aircraft"
General aviation is presently in a high-growth phase and is desperately looking for new aircraft engine technologies. About 65% of this market is in the USA and the Americans are not developing suitable new engines. The results of KERO are expected to be already marketable in 2010, as soon as FAA certification is available. Petrol-fuelled versions are already in production and the kerosene version will use many of the same parts. Parts are manufactured by a range of companies, mostly in Europe.
EUREKA labelling played a key role in obtaining funding for the Mistral Engines’ development. “While we managed to start the work with ‘pocket money’,” explains Geles. “EUREKA labelling enabled us to find the 10 million euro in private equity financing that we needed to see the project safely through to a fully certified product ready for manufacture.” Most of the technical problems have already been overcome - one problem still being tackled is pushing away the detonation, or pre-ignition, limit. Nevertheless, Geles predicts full FAA certification within 18 months of the project ending. The sky is then literally the limit!