Is the Rotary Engine an Obsolete Contraption

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SkyActivG

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I have always loved this motor from Mazda, but it's looking more and more likely that this motor will not make a come back. I have come across countless SkyActiv Rotary articles, but they date back to 2012. I'm not even sure how an implementation of SkyActiv would work on a Rotary engine. It seem too sophisticated, which will most likely effect reliability.


Thoughts?
 
Felix Wankel was an expert and innovator on sealing systems, and strangely, his engine design has the longest seal length to swept volume ratio of any production engine (Renault/Rambler beat it in the 60s 70s, and Sarich slaughtered both of them in the 80s but neither of those made production).

Wankel has a long flame path, seal/lubrication issues, and really only exists for novelty value, if at all these days.
 
My old boss had about 6 different Mazda rotaries over the years including 2 new models. Every single one drank oil including both new Mazda RX-8's. The dealer said it is normal. The rotary engine design is tough to meet current emission levels due to its design.

Dave
 
A friend of mine bought his daughter an RX-8 and put two engines in it to get to 100K and he is particular about maintenance. The tech at Mazda said it is really not uncommon for them to need overhauls every 60K or so. In fact Mazda paid for the engines each time when he complained which tells me one that it is common and two, that they do offer excellent customer service.

It is neat in that it is a workable alternative internal combustion engine. However, the only real benefits are the minimum of moving parts and its compact size. While the benefit of fewer moving parts was of some value a few decades ago, most piston engines are reliable and most drivers no longer harbor much trepidation towards their increasing complexity. As to size few cars can’t find room for a four cylinder or even a small turbo to boost it. Add to that a few of the negatives, oil consumption, relatively short overhaul intervals, and lousy comparable fuel economy and it amounts to little more than a neat engineering and conversation piece.
 
I love rotary engines...
But I think you put it perfectly - they're an obsolete contraption, destined to be relegated to history. Their only real advantage is high power to weight ratio, but these days, small turbo engines seem to be the way to go.
 
I've owned two RX-7s and as much as I wish it weren't true, I think it's time to put the rotary engine out to pasture. They were fun for me for a while, but I'll never own another one... which is a shame because the RX-8 is one of the nicest driving street cars I can think of.
 
The basic design of the Wankel goes against achieving compression ratios much over 9:1 and still having a good combustion chamber shape ("good" means low surface to volume ratio). Being limited in compression ratio makes good efficiency hard to achieve.
 
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The Wankel engine is an example of where - though the engine was theoretically superior to the piston engine - it couldn't meet practical considerations.
 
Originally Posted By: Kestas
The Wankel engine is an example of where - though the engine was theoretically superior to the piston engine - it couldn't meet practical considerations.


Couldn't have said it better myself.
 
The downsides being high fuel consumption and high emissions could be resolved by natural gas and/or hydrogen. Both burn cleaner and might cost less per gallon/unit energy.

But yes unfortunately for gas I think it's negatives outweigh it's positives especially since saving 50 lbs on an engine doesn't matter much when a compact car is pushing 3000 lbs.
 
Absolutely true! Engineering theory and practice are two different animals.....
But I wish Mazda would keep the RX 8 and simply put a sky active engine in it - base 2.5 for the base model and then a turbo'd engine for the optional ( upgraded ) one. Would probably give lots of other sports cars fits, including Mazda's own Miata. But at least the RX model would a coupe instead of a convertible.
 
Originally Posted By: Kestas
The Wankel engine is an example of where - though the engine was theoretically superior to the piston engine - it couldn't meet practical considerations.
When I was in auto shop in 1970, the teacher thought the Wankel engine was the next big thing. I thought it was weird, and was wondering how it could be used. But a friend of mine bought a Mazda in the mid '70's that had one in it. If I recall correctly,it had a anti-freeze injection system on it?. Still today with all the technology there is in the world, unless your 3 ft tall, and weigh 50 pounds, you won't find a gas powered car that gets 40mpg plus.,,
 
In 1974 I went to a university lecture about the Wankel engine technology. Most of the presentation was about the three-lobe design. The presentation also included four-lobe, five lobe, and more-lobe designs that were theoretically possible. The number of lobes were limitless. But the practicality of these multi-lobe designs was essentially nil.
 
So from what I've read so far.... The primary set backs for the Wankel Rotary are:

1. Bad mpg
2. Burns oil
3. Cannot seem to be brought to stringent emissions standards.
4. Cannot use synthetic oil

Can any of these solutions be resolved? To me oil burning isn't an issue since the Wankel is run on Conventional oil and thus being cheaper to top off.

The Emissions and bad fuel economy seem to be obstacles that cannot be bypassed because of the design of the motor.
 
As a previous rx8 R3 owner I will say the rotary engine was fun if you were in the mood to keep the engine screaming above 5k rpm. For casual driving it was a pain. No power around town below 4k rpm. No passing power without downshifting 3 gears on the highway. It sounds amazing and is butter smooth, but it only gets 20 mpg all highway.

The rotary design is great, but it simply doesn't deliver the type of power and efficiency that consumers demand. I consider it a novelty. It takes knowledge to maintain and skill to keep it in its powerband.

All that aside I believe the rx8 would have been a success if the 1st generation cars 04-08 would have been more reliable. By 08 it didn't matter that the next generation was the most beautiful car on the road because people were scared to buy them. The redesigned 09-11 cars have proven reliable, unfortunately Mazda was 5 years late on making the renesis engine reliable.

Mazda should bring the rx8 back with a turbo 4 or a lightweight v8. The car was one of the most confident and best handling cars I've ever driven. I would have loved to take the R3 edition I had and have the LS1 and t56 out of my corvette under the hood. The lsx engine is not terribly more heavy than the rotary, so the balance is still relatively close to the same. 350hp and a car that handles that well would be a world class car.
 
Originally Posted By: SkyActivG
So from what I've read so far.... The primary set backs for the Wankel Rotary are:

1. Bad mpg
2. Burns oil
3. Cannot seem to be brought to stringent emissions standards.
4. Cannot use synthetic oil

Can any of these solutions be resolved? To me oil burning isn't an issue since the Wankel is run on Conventional oil and thus being cheaper to top off.

The Emissions and bad fuel economy seem to be obstacles that cannot be bypassed because of the design of the motor.


Note that the Mazda race team used synthetic oil in their rotaries.

My Dad had an RX-2 and an RX-4, I used to beat them both mercilessly as a youngster. I once took money from a GTO in the RX-4. Car and Driver set a land speed record in a rotary Mazda long ago. My bud had a nifty 85 Turbo II that was an amazing car for the money.

The engine is far from a contraption, it is actually an elegantly SIMPLE engine that defies most folks understanding. With proper apex seals and some redesign it could no doubt be made to work but it will never be as efficient as the engines everyone compares it to.

I always felt all the RX-8 needed was another rotor!
 
Originally Posted By: double vanos
Absolutely true! Engineering theory and practice are two different animals.....
But I wish Mazda would keep the RX 8 and simply put a sky active engine in it - base 2.5 for the base model and then a turbo'd engine for the optional ( upgraded ) one. Would probably give lots of other sports cars fits, including Mazda's own Miata. But at least the RX model would a coupe instead of a convertible.


Totally agree. I have driven them and the handling is amazing. I wish they would have the MX-5 in a true coupe, not a removable or retractable hard-top.
 
Originally Posted By: BigCahuna
Still today with all the technology there is in the world, unless your 3 ft tall, and weigh 50 pounds, you won't find a gas powered car that gets 40mpg plus.,,


The 2014 Mazda 6 and 2014 Mazda 3 both get 40 mpg highway on straight gasoline.
The Fiat 500 can get 40 mpg on the highway, as long as you choose the manual transmission on the Pop version of the car.
I'm sure that there's several more out there.

Welcome to 2013.

BC.
 
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