A carbon-carbon refractory composite Wankel rotary engine without apex or side seals.
The primary purpose of this engine type will be for experimental and light sport aircraft needing between 50-350 horsepower. This is not a limitation. An engine of this type can be manufactured to any power rating needed and to any type of fuel required.
These engines will be manufactured in house.
A provisional patent has been applied for.
Overview
Historically the Wankel engine has suffered from poor fuel consumption and the need to burn oil in order to keep the Apex seals lubricated and cool. Apex seals themselves have suffered from breakage and they cause high friction within the engine at high RPMs. The side seals also contribute to the friction problem and they need to be lubricated as well. The vast majority of the problems of the Wankel engine can be attributed to the Apex seals and lesser so with the side seals.
The whole purpose of the seals is to seal the three different combustion chambers of the rotor from each other. The rotor and the housing surrounding it expand and contract at different rates so the apex and side seals must be able to move in and out in order to compensate for that. So it would seem that without them the engine wouldn't be able to function properly. It turns out that around 1982 the Curtiss Wright Corporation had shown that the apex seals could be retracted at high RPM in order to reduce the friction and improve the fuel economy of the engine. Unfortunately it does require a somewhat complicated mechanism to retract those apex seals.
If the rotor and the housings were made of a material with very low thermal expansion properties, then a very small gap between the rotor and the housing could be maintained at all working temperatures. This could make it possible to not have to use apex or side seals at all which would mean that fuel economy and emissions would be improved greatly. The surface coatings of the housing would not have to be made of a hard material at all, but instead they could be made of an “abraidable” high temperature coating, such as porous cordierite. This would allow the rotor to seat or break into the coating for better sealing. Of course any of the rotor surfaces that makes contact with the abraidable material would have to be made of a rather hard high temp coating. So silicon carbide will be used.
The major portion of the internal materials made of a carbon-carbon refractory composite will make it so a water cooling system would not be needed, substantially reducing fuel consumption. There will be the need to cool the oil and to some degree, the fuel injectors though. This will be especially helpful to aircraft since the side effect is less cooling drag, less complexity, and less weight. On top of that, the engine has a very small footprint in relation to its horsepower which will allow for a much more streamlined aircraft fuselage.
Benefits, applications and comparisons.
Comparing horsepower to horsepower, the simplicity of this design allows for a much smaller and lighter engine package than just about any engine out there except for gas turbines where this engine will be quite similar to the power to weight ratio. However, it will have smaller overall packaging compared to a similarly powered turbine. This will allow for a very streamlined forward fuselage of typical single engine aircraft. Of course, because the engine will be so light, ballast weights will be required to maintain aircraft balance.
Because there will be no apex or side seals in the engine, the TBO can be extended well beyond the very acceptable 2,000 hour mark. More than likely the TBO will extend past 10,000 hours for this engine.
Roller bearings are designed into the engine in order to accurately maintain the position of the rotor, and to reduce friction losses, contributing to better fuel economy and a longer TBO. Using roller bearings also allows for the use of a very low pressure oil pump, which will contribute to fuel economy improvements as opposed to wasting energy on a much higher pressure pump.
For the sake of comparison, the main competitor to the 100 horsepower version of this rotary engine will be the Rotax 912is. At 75% power the Rotax will burn about 5 GPH at minimum. That is based on a BSFC of 0.411 LBS/HR/HP. This rotary engine is projected to burn at worst 3.75 GPH. That is based on a BSFC of 0.3 LBS/HR/HP. This rotary is also far lighter, more compact and less complicated than the Rotax. Prices are expected to be competitive to the Rotax.
The high temperature properties of this engine will make it well suited to burning hydrogen. Mazda has already developed a hydrogen rotary engine that performs well even without using high temperature materials. Fuel economy will be especially important in a hydrogen engine since it is expensive to produce and requires more space than traditional fuels to store. This engine is expected to have close to if not more than a 50% brake thermal efficiency (BTE) which makes it suitable to compete with costly, overweight, and bulky fuel cells.
Other general uses for this engine are boats, inboard or outboard, helicopters, generators, and hybrid range extenders. For military use this engine would be well suited for just about any prop aircraft, especially drones. It would also prove to be useful as a generator for the military since it would be much more compact and lighter than current generators, making transporting them much easier.
The M1 Abrams tank runs an Avco Lycoming AGT 1500 gas turbine. Changing to this rotary engine would allow for a much more compact, quiet and fuel efficient power pack for the Abrams. This will also increase range substantially.