Wankel Rotary Engine: Exploring Why It's Not Used More

[baywax]

Is there a reason we don't see the Wankel rotary engine being used more as an alternative to the piston engine? I've heard different reasons but there must be a reason that its not used in every engine today.

http://auto.howstuffworks.com/rotary-engine.htm

I see that it was first used as an aircraft engine shortly before WW1 and later Norton Motorcycles gave it a "whirl".

 

[russ_watters]

That article lists several reasons. Low efficiency is a biggie.

 

[HallsofIvy]

It is interesting that the Wankel engine was orginally marketed as being both more efficient and less poluting than piston engines- apparently the reasoning was that those are both weak areas for piston engines and since the Wankel was not piston it must be better! Objective testing showed that it was worse than piston engines in both categories.

 

[baywax]

That article lists several reasons. Low efficiency is a biggie.

They typically consume more fuel than a piston engine because the thermodynamic efficiency of the engine is reduced by the long combustion-chamber shape and low compression ratio.

Ah ha. I can see that being a problem. No way to compartmentalize the thing?

 

[Integral]

The rotor seal is a problem, the article says that due to gearing the rotor runs slower, but it has a much higher average speed then a piston. A piston stops at top dead center and bottom dead center, while the rotor of a Wankel is continuous high speed motion. This poses a real materials problem for the seals.

 

[baywax]

The rotor seal is a problem, the article says that due to gearing the rotor runs slower, but it has a much higher average speed then a piston. A piston stops at top dead center and bottom dead center, while the rotor of a Wankel is continuous high speed motion. This poses a real materials problem for the seals.

If there were a more efficient seal developed for this purpose could the low compression problem be reduced if the size of the combustion chamber was reduced by using more than one rotary? So that there would be more than one rotary chamber and they would be smaller sizes? (more moving parts of course)

 

[brewnog]

That said, the Mazda RX7 and RX8 have both been very successful, even if the service intervals and fuel economy are more like an American car than a Japanese one.

 

[Danger]

If there were a more efficient seal developed for this purpose could the low compression problem be reduced if the size of the combustion chamber was reduced by using more than one rotary? So that there would be more than one rotary chamber and they would be smaller sizes? (more moving parts of course)

I'm not entirely sure, but I think that you've hit on the idea behind the quasiturbine.
http://auto.howstuffworks.com/quasiturbine.htm"

 

[NateTG]

If there were a more efficient seal developed for this purpose could the low compression problem be reduced if the size of the combustion chamber was reduced by using more than one rotary? So that there would be more than one rotary chamber and they would be smaller sizes? (more moving parts of course)

Actually, sealing issues are made worse by having smaller rotors because the losses at the seal go as the linear dimension of the rotor, while power and energy production go as the cube of the linear dimension of the rotor. (There is a similar scaling factor for piston engines, and piston rings - the seals - are a very heavily developed and studied technology.)

The Mazda engines do use multiple rotors (IIRC three of them), and have had a number of racing successes. Rotary engines are also still somewhat popular in airplanes.

 

[baywax]

Actually, sealing issues are made worse by having smaller rotors because the losses at the seal go as the linear dimension of the rotor, while power and energy production go as the cube of the linear dimension of the rotor. (There is a similar scaling factor for piston engines, and piston rings - the seals - are a very heavily developed and studied technology.)

The Mazda engines do use multiple rotors (IIRC three of them), and have had a number of racing successes. Rotary engines are also still somewhat popular in airplanes.

Thanks Danger and Nate TG

I guess this one has been figured out

Its so predictable that someone would tell me "the rotary engine isn't mass produced because its too efficient and doesn't sell enough gas". What website or planet were they on?

Was the rotary developed as an alternative to the piston engine or was this a case of parallel inventions?

Thanks again

 

[ray b]

wankel rotary was much later,
1960's first use in a NSU car vs 1880 for the early crude piston engine
mazda started in the 70's to build them
some use in bikes and other stuff

lite and compact but uses more fuel per HP, way more
maybe cheaper to build
but needs a rebuild at less miles then a piston engine

 

[baywax]

wankel rotary was much later,
1960's first use in a NSU car vs 1880 for the early crude piston engine

I found some different data on the inception of the rotary engine... used first in aircraft engines before 1918

http://auto.howstuffworks.com/rotary-engine.htm

I see that it was first used as an aircraft engine shortly before WW1 and later Norton Motorcycles gave it a "whirl".

From the first post in the thread.

 

[ray b]

I found some different data on the inception of the rotary engine... used first in aircraft engines before 1918



From the first post in the thread.

thats an aircraft piston motor that spins in pre 1918 form
it is mostly an aircooling trick setup but still a normal piston motor
not anything like a wankel
there are many kinds of rotarys

 

[Integral]

LOL!
There is little connection between the WWI aircraft rotary engine and a Wankel. The crankshaft of the WWI era engine was rigidly attached to the airframe. Conventional pistons provide the power to spin a massive cylinder head with the propeller attached around the crankshaft. The moment of inertia of the huge cylinder head was a major factor in the handling of the aircraft and therefore in the tactics employed during aerial combat of the era. Both of the commonly known planes of the era, the English Sopwith Camel and the German Fokker Dr1 (The triplane) were powered by rotary engines.

 

[baywax]

LOL!
There is little connection between the WWI aircraft rotary engine and a Wankel. The crankshaft of the WWI era engine was rigidly attached to the airframe. Conventional pistons provide the power to spin a massive cylinder head with the propeller attached around the crankshaft. The moment of inertia of the huge cylinder head was a major factor in the handling of the aircraft and therefore in the tactics employed during aerial combat of the era. Both of the commonly known planes of the era, the English Sopwith Camel and the German Fokker Dr1 (The triplane) were powered by rotary engines.

And so when we say "damn you Red Baron" it is in regard to his disregard of fuel efficency... among other atrocities.(?)

 

[wolram]

The Wankel is still improving.

 

[baywax]

The Wankel is still improving.

Cool! This also brought the idea of the Magnetic Rotary Engine to my attention but the video was about 36 seconds long.

Here's a slightly better look at a Multiple Magnet Engine concept.

http://www.youtube.com/watch?v=So8mhc40pZQ&NR=1

 

[SRode]

Wankel engines suffer because there isn't a large interest in developing them and therefore little money for R&D. Wankels are interesting because they have fewer moving parts and the manner in which they rotate cause little mechanical stress, but suffer horrible efficiency and emissions. Maybe one day, I love an engine that can rev.

 

[robsmith82]

So what's the main advantage of a wankel? Is it more balanced in terms of vibration than a reciprocating piston engine?

 

[ray b]

So what's the main advantage of a wankel? Is it more balanced in terms of vibration than a reciprocating piston engine?

no they don't rev very high do to vibration problems
but as they have three lobes they trippel the real RPM reading
IE A WANKEL AT 2000 RPM READS 6K ON THE TACH

THE MAIN ADVANTAGE IS LOW WEIGHT
it is a lite simple motor
and weight is about 1/2 a normal piston motor of equil power