[chiph]

No 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-pressure seals working. It was in conjunction with Wankel rotary engines, which have always had problems with the rotor tip seals leaking (ask any Mazda RX owner...) This engine has the same problem on the intake/exhaust end, as the piston carrier rotates past the openings.

[BrandonMarc]

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".

[frankus]

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.

[MattBearman]

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.

[phkahler]

You missed one - perfect balance. The CG of a properly designed rotary does not move. It's the reason it can rev so high. And flat torque across most of the RPM range is the reason for the power density since torque*speed=power you increase power by spinning faster. Oh wait, you did say smooth power delivery. It does go together with the others.

[IanDrake]

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

[MattBearman]

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.

[IanDrake]

> I've never flooded mine

Neither had I...just never let a valet, mechanic, or relative try to start your old RX-7 ;)

[Sophistifunk]

We have a bunch of old rotary race cars in the showroom at the 9-5, you wouldn't believe how much noise and oil they put out the back whenever they need to be moved around :)

wank-wank-wank-wank-BANG!-wank-wank-wank-wank

[virtue3]

no torque at low rpm is pretty common among the smaller inline 4 cylinder japanese cars as well ( I really learned stick on my integra GS-R - 189hp 4 cylinder). basically if you don't keep the rpms up when you shift you're just pissing away acceleration power. It was probably more noticeable with the honda engine tho (that vtec).

[grecy]

> "well if (rotaries are) so much better why isn't it more common".

That's a complicated question with a complicated answer, but it basically boils down to there having been hundreds of billions of dollars (trillions?) spent on R&D for traditional (pison, conrod, crank, block) engines, while only a tiny amount has been spent on R&D for rotaries and other "different" designs.

[jccooper]

There is a brief mention of efficiency, but that doesn't seem to be a big point. The port structure does make me think it might be a bit dirty--kinda two-stroke-y.

But not all engines go in cars. Might be a nice one for aviation--though aviation engines are maybe even more handicapped against change than those in automobiles. The experimental aircraft market ain't that big. Other markets where Rotax lives might like it; pumps and such.

Anyway, that's probably another one of the reasons they're not expecting automotive applications in the first generation.

[ew6082]

In this case the sealing issue is probably in better shape than the Wankel, since the seal is located outside of the combustion chamber. I could see something similar to a piston ring in a groove with a wave spring behind it being used no problem.