Fundamental Flaw of Rotary?
 

Had a discussion somewhere else about rotary and someone brought up the topic that despite the beauty of rotary on paper, the design is fundamentally flawed. His argument goes like this:

The combustion chamber of rotary is designed in a way that one side of the chamber is constantly hotter than the other. More specially, since the gas is always injected from one side and ignited on the other, the temperature inside the combustion chamber is always uneven. This will make it very hard to maintain perfect seal (virtually impossible since the whole chamber is made of the same material) over time.

I think this actually makes very good sense. What is your take?

First off, there is no design of anything that is not 'fundamentally flawed' in some way or another.

The uneven thermal distribution is indeed a major engineering hurdle for rotary designers. The technique to mitigate the effects of this, as far as I know, mostly involves creating ideal coolant circulation paths that equalize temprature. (Flowing heat from the exhaust side to the intake side)

[Edit: This *is* why the engine should be allowed to warm up under light-load conditions until it reaches operating temp. The extent to which this 'flaw' has an impact on the driver is speculative.]

i am not saying piston engine is perfect, but it indeed gets even thermal distribution, unlike rotary.

Aren't they trying to at least improve this by making the 16x width lower and spreading the spark plugs out?

OK, I can't edit my posts. It seems to bug out and I can't save. Here is what I was going to include also.

*EDIT* I mean, since that will help the flame front travel, thus better emissions and MPG, in my head, that would help with the temperature, right?

It will help with a more complete burning of fuel, but the core issue is that exhaust is always interacting with one half of the housing and cool (Relatively) intake air is always interacting with the other half.

This will be true for all designs.

[Edit: The seals on one side expanding at a different rate than the other side and causing undue wear before being corrected by heat distribution mechanisms is the problem, not the heat distribution in the combustion chamber itself.]

The other issue I heard of with a moving combustion chamber is that the mixture will always be leaner at the leading edge and richer at the trailing edge of the rotor surface...

My hope is that direct injection can compensate for this effect

The only flaw of the rotary engine is there are not more cars using it!

ha +1

the fundamental flaw of a rotary is static port timing

Everything has "fundamental flaws." Money and engineering time are required to come up with adequate work-arounds.

In short:

It's not even close to even...

The fundamental flaw of piston engines is that it is converting a linear motion to a circular one. That is simple physics that can never be worked around within the description of "piston engine".

Heat distribution can be corrected, so can material usage, seal design, port location and design, ignition methods, air flow paths, rotor geometery, etc...

Compare the Wankle rotary now to when the piston engine had 43 years of development, which was sometime in late 1800s or early 1900s if you take 1856's development of the first piston engine with 5hp, or 1860's development of the first piston engine with "cylinders, pistons, connecting rods, and flywheel". (http://en.wikipedia.org/wiki/History...bustion_engine)

The Wankle is cleaner, more efficient, more powerful, and more reliable... in magnitudes.

Piston engines are not developing in leaps and bounds. Comparatively, the Wankle is.

There are many who would disagree with every part of this statement... with the exception of the 'more powerful' as far as the power to displacement (size) ratio is concerned :)

If you look at the design of the cooling circuit, the lowest temperature coolant (straight from the radiator) goes through the hottest part of the engine (the side with the plugs). Mazda has made some adjustments to the coolant passages a little bit over the years. Now that they are designing a new engine (16X) with different geometry, they have the flexibility to address the issue you speak of further.

Btw, the "fundamental flaw" of the current rotary is too much quenching. The flame fronts extinguish prematurely, resulting in excessive fuel consumption and HC emissions. Mazda is addressing this in the 16X by making the combustion chamber thinner and spreading the spark plugs further apart.

Also, piston engines don't have a "perfect seal." How could they and still be able to move? That's why there are endgaps on the piston rings and gaps between the cylinder wall and piston itself.

See the previous qualifier.

"When the piston was 43 years in development..."

Basically, if you take each type's starting point, and compare them at 43 years in...

"The Wankle is cleaner, more efficient, more powerful, and more reliable... in magnitudes."

Though true, modern technology exists now that didn't then, but even if you triple piston's development time, the statement still holds true.

Yes, but I think there was certainly no comparable effort in the first 43 years of development for the piston engine like there was for the wankel. I mean, in the development of the wankel they could rely on certain knowledge gained about the internal combustion engine in general that they did not have when initially developing the piston engine.
Don't get me wrong, I like the rotary, but I also think that comparing the first 40+ years of the piston engine with the same period for the wankel is not really a fair comparison... they knew a lot more by the time they started to work on the wankel than when they started to do the same with the first piston engines. so not apples-to-apples comparison as far as I can see it. In other words, it was easier for the wankel developers.
If you compare the results of the development of the piston engine in the last 40+ years to the advancement in the rotary technology, I see more results for the piston engines. But certainly it is easier for them to show advancement since so may different companies developed the piston motor while only a handful (and mainly, just one) did the same with the rotary.

I get what you are saying.


I just think that the people that have massive problems with the rotary as it stands today are comparing it to an engine design that has had over a hundred years of development by anyone that decides to make a grab for cash.

The Wankle is only on it's 7th? production iteration with the Renesis? It's made progress in leaps and bounds, and there is still a ton of room to grow and explore. Material usage alone is significant, not to mention geometry.

the rotary may have its flaws, but look at how well it runs and the earlier rotaries (12A and the 13B from the 84-85 SE) were built extremely well and lasted well over 150K miles. i know an SE owner that has 300K on his ORIGINAL engine http://www.rx7club.com/showthread.ph...highlight=300K so despite its shortcomings, is overall an engineering marvel.

+10 :Peace:

So every car makers except Mazda is stupid...?

The few companies such as Mercedes Benz that took on rotary engines for a short amount of period then dropped it even though it's a better design fundamentally?

Sorry, as big of a rotary fan as I am, I simply can't imagine the only thing holding down rotary is profitability aspect of it due to the lack of mass production...

If profitability is the only problem, shouldn't all race cars be rotaries since they are "better"?

Sorry, not a engineering guru, just a consumer raising some common sense queries.

the rotary engine is not 43 years old. Mr Wankel ran his first prototype in 1957 and rotary engines were pursued or used by NSU, Rolls Royce, Suzuki, Arctic Cat, Norton Motorcycles, and John Deere was pushing for their design for military vehicle power plants in the 80's. and i'm fairly certain there had been rotary engines prior to Feliw Wankel(early 1900s), just not the same geometry or as well developed.


see, most all flaws i can think of can be engineered out in other ways... but static port timing cannot be engineered away with current or upcoming technology, not without some serious redisign and enineering. no matter what else you engineer away, you'll always be missing out on a fair bit of power, efficiency, emmisions, economy because of static timing.

ULTIMATELY the rotary engine, as a gasoline engine, cannot compete in the journey to push internal combution engines to their theoretical potential based upon availible technology.

yes all race cars should have rotary engines AND THE FREAKING 24hours of Le mans sanctioning body should allow rotary engines again so mazda can crap all over the other cars so says the mazda 787B from 1991......

agreed!!! the 787B would still crush everyone. then we would see some serious rotary development. 15 years of r&d......imagine a 26B in formula 1?

Indeed… http://www.youtube.com/watch?v=hNQfXdp-2oI