I have heard a bit about it. The biggest thing is that those engines can change a crazy amount of parameters including compression ratio, fuel mixture, valve timing, spark ignition timing, oxygen percentage in the intake, intake air temperature, intake boost pressure, and so much more. To control the intake temperature and oxygen percentage, some exhaust is cooled and some is not so they can recirculate it in controlled ratios. They also have crazy amounts of sensors including pressure sensors in the cylinder, detonation sensors, intake sensors for oxygen content, barometric pressure, flow rate, and temperature, exhaust sensors for temperature and oxygen content, and more. So theoretically you might be able to do something like this with a paramotor engine, but the weight penalties and the complexity would be very significant. At the same time I believe you would also need to go with something like a free valve 4 stroke to get that much control over everything in a ~250cc size engine.
Here is one idea I have had for a paramotor engine.
It’s an old full scale drawing I made to get some ideas down. A running version would be very different.
My design is based off a combination of a Junkers Jumo 205, Achates 2.7 liter engine, and a few different paramotor engines that I have had experience with.
The first and most unique part is that it has an opposed piston design. Opposed piston engines typically have an efficiency increase over comparable 4 strokes by 10-30% simply because of the opposed piston design. They also have more horsepower than a 4 stroke and typically more horsepower than a 2 stroke at a given rpm. These engines typically also have very wide power band and extremely high torque figures. For example the Achates engine produces 650nm or 480 foot pounds of torque and that is from a 2.7 liter gasoline engine! It also produces 360 horsepower at only 3600rpm. One interesting thing about this engine is that I can theoretically make comparable power to a vittorazi with a similar size engine, but with far lower rpm’s which would hopefully improve reliability, combustion efficiency, and the overall lifespan of the engine.
This engine should be very efficient for a paramotor engine. For perspective, the standard vittorazi with stock carb settings is at about 15% brake thermal efficiency (BTE) at a cruise. The vittorazi silent is at about 18% BTE, and the EOS 4 stroke is right around 21% BTE. I believe that a carbureted version of this engine should see something in the range of 25% BTE for about 4.5 hours of flight with a 2.5 gallon fuel tank. Alternate versions with electronic fuel injection and a few other tricks just might see higher than 30% BTE for peak flight times in the 5.5 hour range with a 2.5 gallon fuel tank.
This engine will have many difficult challenges that come with it. Possible the biggest will be the gearbox that will be required to connect the two crank shafts together. This will mainly be challenging as weight is one of the biggest issues that paramotor engines are designed to overcome and most gearboxes on opposed piston engines are very heavy. The next big challenge will be the oil system. At this point I would like to use a dry sump oil system as I don’t believe a wet sup system would appreciate the height difference that could occur between the two crank cases during maneuvers and on the ground. Another issue is scavenging the engine. These opposed piston engines work on a 2 stroke cycle so they can’t replace the fuel/air like a 4 stroke and they can’t use the crank case like a typical 2 stroke because this engine used uniflow scavenging and that means you could only use one crank case which wouldn’t work. So you need to use a supercharger and a way of regulating back pressure which in my designs has always been a valve in the exhaust to allow for high torque down low without restricting top end power.
I would go into more detail on some of what I want to do, but I would legitimately like to try and develop this engine and maybe put it in production if it somehow manages it work well let alone at all.
Theoretical advantages of this engine:
- very low fuel consumption
- low noise
- nearly no vibration
- longer lasting piston rings
- no oil mixing
- high torque
- wide power band
- lower emissions
- can be modified to have no power loss at high elevations
- spark plugs last longer
- lower operating temperatures
- overall longer lasting engine
These are some rough specs I would like to see from a carbureted model, but they could be miles off:
- Displacement --165cc
- Power – 30hp @ 6000rpm
- Weight – 30 lbs
- fuel consumption – as low as 1.8 liters/hour
I know as well as anyone else that things never seem to work as well in the real world as they work in theory, but I still want to try developing this engine that I have been fantasizing over for a long time and just maybe it would work well.