I think the reason they settled on the geometry they did was simply due to the technology of the day. Back then carbs were the way to get fuel into the engine. A rotary has to move air a long way around the engine before it burns it. A piston engine doesn't suffer from this problem. They probably ran many tests and found that with fuel metered in such a manner that the standard geometry that we all know was the most effective. It doesn't mean it was the overall best. Just best with what they had to work with at the time. With direct injection, fuel doesn't have to go as far. It moves inches rather than feet before being burned. This means there is less total surface area for fuel to come into contact with and fall out of suspension.

 

The 16X has larger eccentricity already along with narrower rotors of larger combustion face length. Or do you mean eccentricity relative to rotor size?

Also, with increase in sealing they can increase compression and the larger internal sizes make way for porting improvements. I'd like to see more oval than 8 shaped housings though, I think it would be an improvement in apex seal contact position and speed along with sealing performance.

I'm intrigued by the idea of a very late closing intake port that actually lets compression escape the combustion chamber and be fed to the adjacent rotor. It could open the possibility of a miller-like short compression long expansion cycle that could improve efficiency, something like 10:1 dynamic compression to a 14:1 expansion.

 

I mean eccentricity relative to rotor size.

A more oval shaped combustion chamber would have a shorter effective stroke. It would have a higher surface to area ratio and by default would be less efficient. That's what Mazda is trying to get away from in the piston engines so it only makes sense to avoid it in a rotary as well.

The 6 port engines already have a really late intake closing. Mazda has already played with a Miller Cycle rotary and then abandoned it like they did the Miller Cycle piston engine in the Millenia. Keep in mind that a Miller Cycle engine has to have forced induction just to bring it back to the same power level, albeit at a lower amount of fuel consumption. It's a lot of effort for a little bit of gain.

 

Agreed but a more 8 shaped housing will introduce sharper angles to the apex seal to housing interface making sealing more difficult and stressing the seals more. Im sure Mazda can find a pro/con balance for performance and efficiency.

Miller or Atkinson cycles not necessarily need superchargers, Mazda used it in the Mazda2 sans supercharger and most gas/electrics use it as well.

With today's variable valve technology, direct injection and better sealing this type of cycle can still be beneficial. Mazda is using 14:1 in the highest compression Sky engines, they could keep or lower a little the compression but with a longer expansion say 16:1 or so and extract a little more work from combustion while making the engine work less at compression for a net gain in efficiency.

 

Mazda actually refer to the Skyactiv G as utilizing Miller cycle. Atkinson is a different animal that requires a crankshaft that varies stroke length physically.

I think they are going to implement more Miller with the rotary as well. More than 50% of piston engine Skyactiv combustion techniques will migrate to the rotary I would suggest.

Paul.

 

Did they change the side seals any?

 

How would any of us know?

Paul

 

Side Seals??

When you look at the chromed 16X and 13B (Renny) Rotors in the TMS, the principal design and layout looks the same as did Corner Seals.

Of course a larger Rotor will mean longer Side Seals and Side Seal Springs.

Provided Apex Seal thickness has not changed in the 16X then Corner Seals and Springs will possibly be the same as the 13B Renny?

 

Neither term is really correct in terms of the Otto-cycle "cheat", though I think Atkinson is closer in spirit.

Consider an ideal, very long cylinder, closed at one end, with a piston 1" from that end containing a air fuel charge. The charge is fired. The piston moves away from the high pressure down the cylinder. That motion can do work. In the absence of friction, it will continue to move until the pressure and temperature in the cylinder drops to ambient. 99% thermal efficiency, hoo rah!

Prius, for sure, others, and Mazda probably (I haven't looked into the details) "cheat" their system by building an engine that has "mechanically" a very high compression ratio. In practice however, the intake valves are left open too long, so the effective c.r. is normal, that is, part of the compression stroke pushes air out the intake. This makes the expansion stroke longer that what it would otherwise be, and increases efficiency toward the "long cylinder" ideal, without the complexity of a true Atkinson engine.

Can it work this way with a rotary? Maybe, but the too-long-open intake port with fixed opening an timing would def complicate matters as would the reverse flow pulses migrating up the intake runners.

 

Perhaps a 'fresh air exhaust' port? A small correctly shaped port farther along the rotation designed to explicitly push air out in the same manner? 'Closing' just before fuel injection. Possibly just a 'waste' air dump, possibly used to 'charge something else, like feeding forward into the rotor combustion currently underway for a rush of air to assist in a complete burn? Obviously this would lean that burn, but it could be accounted for with proper initial fueling and placement of where and at what point in the rotation this partially compressed air charge is introduced.

 

The cool thing is I know they are looking at ALL these possibilities and all the old ones anew, now with the aid of very advanced computers as well. Just wait until Mazda has improved sales sufficient to lend some of their hundreds of powertrain engineers from the piston side to push the RE group further.

Paul.

 

That really goes back to what I suspect. They did things the way they did not because it was ultimately the best way to do it but rather it was the best way with the technology of the time. If fuel delivery and ignition control technology were the limiting factors, how would they know if the rest was truly optimized? It appears they realize this. The nice thing is that they are going back to basics. Almost like starting over from scratch. It was an entirely different generation of people developing the engine originally.

 

I bet Mazda engineers read this forum to get ideas

And if they don't they should...

 

The difference between Mazda engineers and us is that we think we know what we are doing! They know what they are doing.

 

Yes I was reading into the Skyactiv Tech and they do use late intake closing Miller cycle on them but it is active at low loads/cruising to improve enconomy and efficiency without taking a performance hit on high load power.

They just won JSAE awards for the Skyactiv Tech including Catalyst tech used on the Sky-D; High CR for Gasoline engines and High efficiency/economy of ICE.

http://www.mazda.com/publicity/relea...5/120518a.html

 

Are these new engines turbocharged? It isn't a Miller Cycle without forced induction. It's an Atkinson Cycle.

 

Agreed, they aren't forced induced but Mazda calls them Miller cycle regradless.

 

Well, whatever one is thinking....a sad period for Mazda is just around the corner....in less than 8 weeks in fact.

This will be the first time in over 40 years Mazda Motor Corp (inc Toyo Kogyo Co Ltd) has not produced a Rotary powered car off the No 1 Line, Hiroshima.

A sad moment also for the team of engineers who assemble the engines, they are specialists...what does Mazda do with them now?

Wouldn't it be fantastic to see a "Breaking Auto News" press release on a new RX-.

I just can not see any all new Rotary happening again for many years, if ever.

Did I say sad,,,

 

Well, holidays? Weekends? I'm sure days have passed without production in the past 40 years. It's really "years" of production, and you can't call "the first year not producing" until the end of 2013 and still no rotary. Which is more than a year and a half away

I'm sure we will need plenty more engines for quite a few years to come

 

HUH...Are you trying to be smart?

Once the last Spirit R comes off the line it will be the end of 'Rotary Production', Mazda has never stopped making 'a' Rotary Engined car before..

Mazda (Japan) does not assemble Rotary Engines or any engines in 'complete or short block form' once the car is out of production and they do not stock pile them as spares.

Distributors (like MNAO or MA) may have stock.

Making OE replacement parts is not what an assembly specialist does.

 

they will have to keep engines in stock for a minimum number of years.

 

No, just pointing out that there was probably gaps between the last of the FD and the RX-8. Not a full year gap, but likely a gap all the same. Unless you have information to the contrary? The "rotaries always in production" has always been a "for that year"


And US Federal law requires that manufacurers must have available / produce all parts for all cars sold here for at least 10 years past the last production date.

So that's at least a 10 year supply of engines that Mazda must be able to maintain.

 

Most of the accounts that I have read here say that you can't get a new rotary engine from Mazda, only Remans. Are you saying that they now need to have a supply of new engines available while they have supposedly been unavailable or do you know something to the contrary?

 

No, it would be the "parts". So they still need to make the housings, rotors, e-shaft, seals, etc...


Which, re-reading ASH's post, he did say "who assembles", so maybe I'm diving down the wrong path.

 

The RX-8 was announced way before the FD finished....there was a 5 month gap before production started...there has been NO announcement of any replacement for the RX-8...that is my point there is nothing to replace that production vehicle.

NO, I don't give a dam what you think about "US federal law", complete new engines are not Made in JAPAN after any model finishes, as are transmissions as are body shells...try buying a complete new factory engine for the Series 1....only re-mans at in US...and it soon/is will be the same for Series 2 engine.

Really, Mazda actually makes replacement parts from more than 10 years.