Wankel Rotary Engine - a question for the engineers.

[Tayne]

Some of you may know that I don't hold the Wankel rotary in high regard, whilst I admire the concept and can see the benefits of light weight, smoothness and power I feel that reliability and some measure of fuel economy should be achievable after nearly 60 years of development and production.

 

The big issue being the difference in temperature and stress between the rotor tips and the body of the rotor leading to loss of compression or hardened rotor tips breaking off inside the combustion chamber.

 

 

 

There's now a company in the US excitedly claiming they have fixed the issue by messing about with the shape of the rotor and the combustion chamber.

 

 

 

 

 

Whilst I can see an advantage there I can't help looking at the three sharp points of the combustion chamber and thinking that the chaps at Liquid Piston have wasted $18million and the last 13 years of their lives dreaming this up.

 

Does anyone with more knowledge than me think they might be able to make a go of this?

 

https://www.wired.com/2016/06/tiny-engine-one-step-closer-powering-drones-electric-cars/

[PhillipM]

No, thinking the same thing, the ports and edges look like just as much of a sealing issue, along with poorer performance.

[dollywobbler]

It does seem that they've just replaced the high-stress rotor tips with three high-stress points on the casing. It's a lot easier to change rotor tips than the casing...

[rainagain]

I can't help feel that the fuel efficiency will still be poor. The problem with a rotary compared to a conventional piston engine is the larger surface area of combustion chamber means more heat is lost and not converted into motion. I can't see how this engine gets round this. Rotary engines are still used frequently for machinery that needs a high power output in a compact space, where fuel economy and longevity aren't primary concerns.

[dugong]

Cool thread. A British firm claims to have been working on something similar:

 

http://www.autocar.co.uk/car-news/concept-cars/ground-breaking-rotary-engine-created-british-firm

 

I know you love pedantry so I'll just quietly point out that - in strict historic terms - Wankels and Rotarys [sic] are two different engines and should be referred to separately.

 

'Wankel' refers to the NSU/Comotor designs and the latter 'Rotary' belongs solely to Mazda engines. You had licensed Wankels and licensed Rotarys [sic]. AvtoVAZ, for example, ripped off Mazda's 13B solely for Sam Glover's benefit, so you'd call it a knock-off Rotary.

 

Call LiquidPiston's engine whatever you like - it's an, er...inverted Rotary, I suppose.

 

I suppose this is my hardpoint saw post. Carry on.

[Guest Hooli]

Hang on a country that thinks a pushrod V8 is high tech & race cars should only turn left had achieved an amazing break through with technology?

 

I'm not convinced.

[Junkman]

This:

 

 

is not an American engine that works.

 

 

This:

 

 

is an American engine that works.

 

I am an engineer, but I think I managed to explain a highly complex scientific matter so that even the less technically inclined will understand.

[toejam]

The Sopwith Camel bipe had a rotary 

[Asimo]

Doomed. Another attempt to solve a problem no one has.

Reciprocating piston engines work and they are very cheap to make because it is easy to make round parts and round holes. Their combustion chamber surface to volume ratio is always going to be hard to beat. That recent dual-expansion engine (McClaren?) someone popped up here is possibly the way to go.

[cort1977]

Sadly I highly doubt this will ever come to anything.   If Mazda can't solve the inherent issues with rotaries in 40 years of development then I doubt that these punters have done so.

 

They might do well out of it though, some Australian guy managed to somehow leverage a rotary type engine that didn't work in to a A$1Bn fortune.

 

https://en.wikipedia.org/wiki/Ralph_Sarich The orbital engine never even ran properly but was used to extract funds from the Australian federal government, Michigan state government and various corporations who should probably have known better.

[Tamworthbay]

Rotaries are awesome, who gives a toss if they are less efficient or not practical, they are still worth pursuing. Look at the 'jet' cars, dead in the water but it's still brilliant that they tried.

[toejam]

If only someone could invent an electric rotary....that sounded like a V8

[Junkman]

That recent dual-expansion engine (McClaren?) someone popped up here is possibly the way to go.

 

I don't think so.

I think this is the way to go:

 

 

Because for half a century, there was nothing, I repeat: nothing, that could beat a yank V8 in straight line performance.

Nothing. Nothing whatsoever.

 

Now King Kong has arrived.

[RustyNuts]

 If Mazda can't solve the inherent issues with rotaries in 40 years of development then I doubt that these punters have done so.

 

To be fair Mazda still can't solve over heating, failed head gaskets and pistons that explode through the engine casing. They wouldn't be my first choice to work on research into rotary engines.

[Guest Hooli]

If they want to make fancy engines, can we have mini Deltics in cars please. The only thing that can challenge a V8 for noise (Except for aero engines like Merlins obviously).

[Tayne]

I know you love pedantry so I'll just quietly point out that - in strict historic terms - Wankels and Rotarys [sic] are two different engines and should be referred to separately.

 

'Wankel' refers to the NSU/Comotor designs and the latter 'Rotary' belongs solely to Mazda engines. You had licensed Wankels and licensed Rotarys [sic]. AvtoVAZ, for example, ripped off Mazda's 13B solely for Sam Glover's benefit, so you'd call it a knock-off Rotary.

 

Call LiquidPiston's engine whatever you like - it's an, er...inverted Rotary, I suppose.

 

I suppose this is my hardpoint saw post. Carry on.

 

Do you mean that Mazda's marketing doesn't use the term "Wankel", or that their's is sufficiently different to cease to be the Wankel engine they licensed in 1961?

 

The motoring press tends not to differentiate and this wikipedia page doesn't help.

https://en.wikipedia.org/wiki/Mazda_Wankel_engine

 

 

Research this evening has also revealed that the term "rotary engine" (predating our Felix) can refer to an engine where the cylinders (usually in a radial configuration) rotate around a fixed crankshaft.

Who knew?

[Guest Hooli]

I knew, the Sopwith Camel had one of them.

[dugong]

Do you mean that Mazda's marketing doesn't use the term "Wankel", or that their's is sufficiently different to cease to be the Wankel engine they licensed in 1961?

 

The motoring press tends not to differentiate and this wikipedia page doesn't help.

https://en.wikipedia.org/wiki/Mazda_Wankel_engine

 

 

Research this evening has also revealed that the term "rotary engine" (predating our Felix) can refer to an engine where the cylinders (usually in a radial configuration) rotate around a fixed crankshaft.

Who knew?

Mazda's engineers and marketing division felt it had improved the Wankel sufficiently to warrant a new name - Rotary.

It built a rough prototype nicknamed the 'Smokey Badger' more or less as NSU intended; by the time the Cosmo Sport/Cosmo 110S arrived, Mazda claimed over 100 improvements had been made.

 

Yeah, I was aware of the piston engined homophone. Wankels are still Wankels and (Wankel derived) Rotarys [sic] are still (Wankel derived) Rotarys [sic]. Call the new designs whatever you want - I know how precise you like to be. I prefer BRACKETS. 

 

Can I sign off with a quote? I think it needs replacing. 

 

 

I didn't answer your original posted question, soz. Ask someone with a doctorate in engineering. 

[Matt]

 

I don't think so.

I think this is the way to go:

 

 

Because for half a century, there was nothing, I repeat: nothing, that could beat a yank V8 in straight line performance.

Nothing. Nothing whatsoever.

 

Now King Kong has arrived.

 

Yep. I'm stoked to see where electric technology takes the car industry. Clean, quiet and can deliver performance unlike almost anything that we have seen before. The Model S is a two ton, quasi-luxury saloon and the new P100D supposedly does 0-60mph in two and half seconds. Only the top end is missing, 154mph top speed but who gives a flying fuck about that when you have just shy of 1000 N-m of torque available from 0RPM?

[Uncle Jimmy]

Couldn't both the NSU and Mazda engines be referred to as 'oscillating' engines?

[dugong]

Couldn't both the NSU and Mazda engines be referred to as 'oscillating' engines?

Yes.

 

As could the LeRhone Radial/Rotary. The crank (or equivalent) moves eccentrically, too.

 

Mazda wanted to show off its 'mastery' (and I must stress 'mastery') of the Wankel it licensed by calling its improved engines "Rotary."

 

Ramelli had the right idea; his epitrochoidal envelope designs (Wankel/Rotary) should have remained a pump.

 

As for range, yer common or garden RX-7/8 would probably be stuffed by an EV now. Both have had decades worth of development - neither are where they need to be in terms of mileage.

[Station]

I feel that reliability and some measure of fuel economy should be achievable after nearly 60 years of development and production.

Engine is reliable for at least 60,000 miles (and beyond - loads go into 100k) which IMO is perfectly acceptable, and fuel economy - are there any other cars just shy of 300bhp stock that gives good mpg? I get 35mpg on a run - show me a V8 that can do that!

I'd rather change rotor tips on 40kg engine than piston rings on an iron blocked V8.

You don't get Lamborghini or Ferrari owners moaning about their V12 fuel economy ever.

 

What are the problems with these engines? They've just got a bad rep by lazy top ten list soundbite obsessed motoring journos.

[dugong]

Engine is reliable for at least 60,000 miles (and beyond - loads go into 100k) which IMO is perfectly acceptable, and fuel economy - are there any other cars just shy of 300bhp stock that gives good mpg? I get 35mpg on a run - show me a V8 that can do that! You don't get Lamborghini or Ferrari owners moaning about their V12 fuel economy ever!

 

What are the problems with these engines? They've just got a bad rep by lazy top ten list soundbite obsessed motoring journos.

 

 

Rotarys [sic] are awesome and I still want an FD RX-7. 

 

Er...

 

High oil consumption, huge gobs of CO2, poor hot starting, emissions difficulties and varying MPG are all common complaints. Mazda couldn't get the RENESIS to run clean enough for Europe so quietly shelved it. Rotarys [sic] lived for a bit longer in Japan and there's speculation Mazda's developing another.

 

I reckon you might get a basic LS-engined Corvette C4 or 5 into the high twenties / early thirties if you went gentle. I managed 28mpg from the C4 I tested once; IIRC it was a 350 TBI.

 

Mazda still deserves respect for sticking with the Rotary after everyone else fell by the wayside. Rolls-Royce's Wankel tank would've been fun, and I wouldn't mind a go on an Evinrude Wankel snow mobile.

[Station]

That sounds like recycled facts and figures from Crap Cars book Jon, check some of the RX7 forums for real world figures. Apart from topping up oil and as I said rebuilding, I can't see a problem.

[Guest Hooli]

Nowt wrong with them except needing a regular rebuild, sounds like the 1930s...

 

 

I like rotarys as a daft idea to replace pistons, but they just don't seem to work.

[dugong]

That sounds like recycled facts and figures from Crap Cars book Jon, check some of the RX7 forums for real world figures. Apart from topping up oil and as I said rebuilding, I can't see a problem.

 

Are you going foamer apologist on me? I'm no Rotary hater. You know that. 

 

You best tell the Rotary specialists I've spoken to that they're rehashing their facts and figures. 

 

Why did Mazda shelve the RENESIS, then? Why doesn't it have a Rotary halo car now? 

Why are so many RX-8s in scrapyards? 

 

I can't say I'm aware of many LS V8s that need rebuilding after 60,000 miles, either - and yes, SBC swapped FDs of any kind are sacrilege. 

I wasn't aware I was slagging Rotarys [sic] off; they have inherent issues which shorten their lifespan but it doesn't stop them being fabulous (if fragile) lumps.

You're right though, no one buys a Ferrari or Lamborghini for ease of maintenance; it's part and parcel of owning something quick. 

 

Rotarys [sic] ended up as performance engines because the sports car market was the most tolerant of its failings. Mazda tried to sell cooking versions and they bombed - the average owner simply wasn't prepared to put with the histrionics. Remember luckyseven's threads on Retro Rides? His cars were the most pampered things you've ever seen; his FD still failed spectacularly and he still adores them.

I love Rotarys [sic] but I'd never have the financial stones to run one - simply because I couldn't afford the cost of failure when (not if) it occurred. 

Dammit, AS, I tried. I really tried. 

 

I am not plucking these comments out of my arse  -  and it upsets me that you think I'm doing so. As we've discovered on this forum, if I question something, the insults come back ad hominem. That's a very specific message I'm getting.

 

I hear you. I don't have to be here. 

[Ghosty]

I'm seeing a problem with the 'improved' rotary.

The rotor shaft bearings wear, the rotor starts to wobble, and the inlet thing in the rotor catches on the protrusions in the casing. Either the rotor catches and the engine seizes with a big clunk and a stripped gear or something, or part breaks off the rotor, something something Mazda.

[garethj]

Looks like there are still some very high stress points on that new engine so I'm not sure it'll fix the issues of previous rotary motors.  However an education and career in Engineering has taught me that you can't do a technical evaluation based on a gif animation and nothing else.  I'm continually amazed what dodgy designs can be made to work once the materials scientists have got at it, coming up with metals that are harder than Vinnie Jones.

 

Interesting though, and I'm glad people still come up with this stuff.  Just like Elon Musk having the single mindedness to make electric cars viable you've got to be very determined to stick two fingers up to the general public and say "I can make this idea work", even though most of them fail.

[seth]

I think that new design does improve the situation of a couple of the issues mentioned so far. 

One of the problems with the old rotor tips was keeping them cool.  By effectively moving the sharp rotor tips to three sharp points of the housing their temperature can be much more easily managed and so failure would be much less likely. 

Also someone mentioned the heat loss due to the combustion chamber area.  Similarly that new rotor is so hollow and spindly perhaps that can also be effectively cooled?

 

The application mentioned in the article about these being used as single speed generators in a hybrid vehicle makes a lot of sense.

[daveb47]

My favorite rotaries