It seems to share some things in common with the rotary, like moving the ignition chamber past the fuel/exhaust ports, rather than opening/closing valves. So it will need some way to seal the cylinder during compression/ignition... will those seals tend to break up at 100,000 miles like a rotary's apex seals?
Duke Engines' compact, lightweight valveless axial engine
11–20 of 58 posts
Re: Duke Engines' compact, lightweight valveless axial engine
#12Wow. That looks inspired by a helicoptor's swashplate driven from the rotor side. Always fun to see an alternative engine design.
Re: Duke Engines' compact, lightweight valveless axial engine
#13No mention of meeting fuel economy and emissions requirements. Both of those are big topics that engine builders have to consider, with the 35mpg fleet-wide average that cars sold in the US must meet in about a decade. Having grown up in an age filled with car exhaust from carburated engines, I don't miss it a bit -- I like having clean air. One of the comments to the article mentioned the difficulty in keeping high-…
Thank you. I'd wondered how this would compare to a rotary engine. It's interesting how enthusiastic the rotary-engine crowd is, since my takeaway was always "well if it's so much better why isn't it more common".
As an RX8 owner (and enthusiast), I can tell you Wankel Rotaries aren't categorically better, or worse. They have strengths and weaknesses:
- The vast majority of rotaries will need a full rebuild before 100k - worse
- They rev to 10,000 RPM with an unbelievably smooth power delivery - better
- I'm lucky to see 22 mpg - worse
- The engine is so small and light that the RX8 has perfect 50/50 weight distribution - better
- If you turn the engine off before it's warm it can flood - worse
- 231 bhp from a 1.3 litre engine? - better
Oh, and the noise - BETTER!
I do believe with more time and money invested the Wankel Rotary could be better than a standard Otto Cycle IC engine in every way. But electric is the future now, so that won't realistically happen.
Re: Duke Engines' compact, lightweight valveless axial engine
#14No mention of meeting fuel economy and emissions requirements. Both of those are big topics that engine builders have to consider, with the 35mpg fleet-wide average that cars sold in the US must meet in about a decade. Having grown up in an age filled with car exhaust from carburated engines, I don't miss it a bit -- I like having clean air. One of the comments to the article mentioned the difficulty in keeping high-…
Thank you. I'd wondered how this would compare to a rotary engine. It's interesting how enthusiastic the rotary-engine crowd is, since my takeaway was always "well if it's so much better why isn't it more common".
The short answer is that they're difficult to seal and the combustion chamber shape is awful (it looks like a flattened figure eight in cross section).
It's super tempting as an engine designer to take something that works well as a fluid pump and try and turn it into an internal combustion engine. But sealing and lubricating a combustion engine is a much more difficult problem than sealing and lubricating, say, an oil pump. Plus, in order to meet emissions standards, you need to worry about things like flame propagation and avoid little nooks and crannies where unburnt fuel mixture is likely to hide.
Usually the limited success of these sorts of engine designs isn't a case of a mad genius being too far ahead of his/her time, but rather that the advantages, however compelling, don't make up for one or more fatal flaws.
Re: Duke Engines' compact, lightweight valveless axial engine
#15The money quote, for the TL;DR crowd: "Duke Engines' 3-liter, five cylinder test mule is already making a healthy 215 horsepower and 250 lb-ft of torque at 4,500rpm – slightly outperforming two conventional 3 liter reference engines that weigh nearly 20 percent more and are nearly three times as big for shipping purposes. With an innovative valveless ported design, the Duke engine appears to be on track to deliver su…
215hp out of a 3 litre is shockingly low except for a naturally aspirated carburator engine from the 80's.
For example the 2 litre 2015 Mondeo Turbodiesel gets 210bhp.
The article is interesting but reads like a marketing release, the weight saving is the interesting take away I think if reliability matches a modern diesel.
Re: Duke Engines' compact, lightweight valveless axial engine
#16Earlier quoted context omitted.
Thank you. I'd wondered how this would compare to a rotary engine. It's interesting how enthusiastic the rotary-engine crowd is, since my takeaway was always "well if it's so much better why isn't it more common".
As an RX8 owner (and enthusiast), I can tell you Wankel Rotaries aren't categorically better, or worse. They have strengths and weaknesses: - The vast majority of rotaries will need a full rebuild before 100k - worse - They rev to 10,000 RPM with an unbelievably smooth power delivery - better - I'm lucky to see 22 mpg - worse - The engine is so small and light that the RX8 has perfect 50/50 weight distribution - bett…
Learned stick on my second gen RX-7...
-Almost no torque at low rpm - worse
-Easy to flood, then once flooded major work - worse
-Feed it a quart of oil every 1,000 miles - worse
Re: Duke Engines' compact, lightweight valveless axial engine
#17The only ICE advancement that really seems interesting to me is adding an extra cycle to inject distilled water into the cylinder for an extra power stroke.
The idea being that the heat from the prior explosive power stroke is used to turn the water into steam. Now you're using wasted heat energy and removing the need for cooling components.
Re: Duke Engines' compact, lightweight valveless axial engine
#18Axial engines go back a long way, to at least 1917.
https://en.wikipedia.org/wiki/Axial_engine
That format is widely used in hydraulic systems, and is the basis of continuously-variable hydraulic transmissions. Classically, it has problems at high RPMs, but is well behaved at low ones.
It's an idea that might be worth looking at again. With better materials and controls, it might work. The geometry is more flexible than with Wankel engines. The elegant Wankel geometry means there aren't many parameters that can be adjusted to improve combustion. In a piston engine, you can design piston face geometry, cylinder head geometry and fuel and air injection points for better combustion. With a Wankel, you're kind of stuck with the geometry. We'll have to see how this new approach works on pollution control.
Re: Duke Engines' compact, lightweight valveless axial engine
#19Earlier quoted context omitted.
Thank you. I'd wondered how this would compare to a rotary engine. It's interesting how enthusiastic the rotary-engine crowd is, since my takeaway was always "well if it's so much better why isn't it more common".
As an RX8 owner (and enthusiast), I can tell you Wankel Rotaries aren't categorically better, or worse. They have strengths and weaknesses: - The vast majority of rotaries will need a full rebuild before 100k - worse - They rev to 10,000 RPM with an unbelievably smooth power delivery - better - I'm lucky to see 22 mpg - worse - The engine is so small and light that the RX8 has perfect 50/50 weight distribution - bett…
[deleted]
Re: Duke Engines' compact, lightweight valveless axial engine
#20Earlier quoted context omitted.
As an RX8 owner (and enthusiast), I can tell you Wankel Rotaries aren't categorically better, or worse. They have strengths and weaknesses: - The vast majority of rotaries will need a full rebuild before 100k - worse - They rev to 10,000 RPM with an unbelievably smooth power delivery - better - I'm lucky to see 22 mpg - worse - The engine is so small and light that the RX8 has perfect 50/50 weight distribution - bett…
Learned stick on my second gen RX-7... -Almost no torque at low rpm - worse -Easy to flood, then once flooded major work - worse -Feed it a quart of oil every 1,000 miles - worse
No torque at low RPM is true, but I've not found it to be an issue. I use the engine in the same way as I do on my motorcycle - pretty much always above 4000.
The flooding issue I mentioned. It may have been different with the RX7, but the RX8 has a de-flood procedure that works 9 times out of 10. And failing that a bump start usually does it. Although I've never flooded mine, I'm always careful not to shut her down cold.
Oil usage in the real world is not much worse than many other performance cars, in fact it's better than most Honda S2000s. But for people who are not used to having to regularly top up oil I could see it being a ball ache.