What are the draw backs of going 3 rotor with the same displacement?

I ask because I wonder about the possible reasons Mazda has not done this already.

 

as i thought agoogle of the relative terms now does not find the article i previously read.

however- so a 3 rotor of the same displacement but with more square combustion chambers? increase the available torque and increase the efficiency?

 

come to think of it - was it Richard that said something about combustion chamber shape?

 

While I do remember the advantges of the side exhaust RG stated earlier in other threads.

As we all know, the peripheral port exhaust setup will never pass emissions (ie. older 13Bs), I think that is the main reason why we have our current setup in the Renesis. But however, with Direct Injection technology in the Renesis, could we stick with the side intake and go with peripheral exhaust once again?.

With DI, most (if not all) of the fuel will be burned during combustion. And no unburned fuel will be swept out of the pport exhaust. Is there power to be had with this setup? This might introduce overlap and other disadvantages of the older 13Bs, but it seems like the side exhaust is really limiting power output, and I know for a fact that in race engines, pport intake and exhaust is best for power.

Now the problem with this is I am not sure if ALL the fuel will be burned with DI in a rotary engine combustion chamber.

If this works, it is much easier to make a 1.3L 3-rotor than Renesis based(side intake+exhaust) 3-rotor.

edit: Maybe you could slap an extra spark plug in too, however that'll never happen from the factory , 3 per rotor.
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AllDayFunnn

 

my guess is this: The current design of Mazda's rotary engines are heavy (due to the iron-aluminum sandwich). One, you'd be increasing the weight of the engine significantly. Two, rotary engines are not very efficient, due to the design. So adding an extra, inefficient rotor, seems to me like it would just further reduce the fuel efficiency. It's hard enough to sell the current fuel efficiency.

I would like to build a 10A based 3 rotor though, just because. People always want the max power out of their cars, I just like a little oddity and sideways thinking. It'd probably sound pretty cool too. Maybe slap it in an old Volvo...hmm

 

There were many compainies back in the late 50's / early 60's that bought into the Wankel experiment and a vast amount of data and configurations were tried. Some were quite large. I have a book that talks about all the phases that it went through, from Wankels days with valve train work in the 20's up to 1998 and it even has some things about the then prototype RX8.

Allis chamers was heavily working the Wankel and did some of the best work on many fronts. I understand that the final dimensions are set within rather narrow parameters for the motors to work with any effieciency and reliability. Size is scalable but the relationships within the motor are not easlily changed. More than 2 rotors causes significate issue for the main shaft as it has to be made in two-pieces after two rotors right ?!?!

Wankel original design is not even what we have today since 1958 as the Wankel. The original was a true rotary spinning up to 25k with two housings and the carburator and spark plugs deep inside the motor. I believe it was an engineer that he worked with that changed it to the current base design so the could more effienently get the power off the rotating member.

I actually did a report paper for it at school in 10th grade with a mathematical calculation demonstration but I got an F because the teacher said I cheated and used someone elses work, that I couldn't understand it myself. Well that's not true but I can drive the hell out of it when my dad let's me.

I have an ISBN for the book if anyones interested, not sure where we got it but it is quite complete with lots of drawings and explainations etc.

Great,
Jeff B.

 

id love to take a look at that book. whats the isbn?

 

OK, I will post it but I'm at the Univ. in minneapolis now so I will have to call and get it from home. Check back tomorrow latest, it will be here. Maybe I will get a picture of the front cover too. We got it off Amazon i'm sure, in the spring of 2004.

Great, Jeff B.

 

Gee, I'm sure Mazda has not considered all the ideas posted before. I know they only spent $20.00 on rotary research. Damn amazing they got the HP they did with no FI in the 8. They are probably tying to improve both HP and fuel economy, and hopefully will see some results in the next 2-3 years. Turbo? yea, thats why the old 7's got such a bad rep, they blow the seals, if they come up with something reliable I'm sure they will sell it. Never buy a tubo'd car used, it was abused

 

"Hats off gentlemen - a genius."

• - Robert Schumann on first hearing a young Chopin

"Hats back on gentlemen - an idiot."

• - Robert Schumann on first hearing P.D.Q. Bach

• - MazdaManiac upon reading post #59 in this thread.

 

Been a few times to *** in Germany for EFI Technology (the European company, not the Inc.) tech support on the following engines : VW 2.0 TFSi (direct injection, turbo, VVT) and VW 1.4 TSi (direct injection, supercharger and turbocharger, VVT) running from an aftermarket Euro-12 ECU. Works fine. Controlling the injectors is not a real problem. It's the high pressure fuel pump that's a bit of an issue, especially as the change from engine to engine (2 lobes, three lobes...). Special hardware and software, but nothing an up-to-date ECU development company can't get sorted out.

I guess the main issue with DI in a rotary is the fact the combustion chamber moves so much. Difficult to perfectly control the mixture and ensure ignitability in all speed and load conditions. The extra hole in the housing might also reduce fuel economy (due to leak over the apex seal from the high pressure combustion side to the lower pressure compression side).

And on a side note : more threads like this please!

Fabrice

 

OK, here is the ISBN on the Wankel book.

ISBN 0-7864-1177-5

The Wankel Rotary Engine.

(Picture of cover below.) And it was Curtiss-Wright not Allis-Chambers as a huge developer of rotary technology in the early days with Germany's NSU where Wankel himself worked. (circa 1959 -1966) Curtiss-Wright built a 1920 cu in. monster wankel motor that made 872 hp. They built the first multi rotor unit and everything in between including ones that ran on every concievable fuel of the day.

Great,
Jeff B.

 

I've got that book.

 

And I just ordered it.
Hope it's worth the money.

 

Yea, it is a great rotary reference and history that is fact based. I didn't read any others that were as concise. Hope other will find it a help.

Great,
Jeff B.

 

Rotarygod, I'm new to rotaries, to the RX8, and to this board. I thank you for this and other posts that have contributed to to my knowledge base on the subject.

Your posts bring a couple questions to mind, both about apex seals. Bear with me on one one question, please, as I try to apply a little of what I know about piston engines here (my piston experience is with Harleys). I hope that won't get me banned.

The non-piston question is this: The apex seals are subject to a high degree of centrifugal force as the rotor spins, or so I would suspect. Does this have any effect on seal-to-wall scraping pressures, and thus on wear rates of the seal as RPM increases? Or are they held tightly captive in their grooves? Knowing that springs are under them makes me think they are not held tight.

Next question, and it's sorta complex.

The oil scraper ring groove on a lot of pistons is perforated so that crankcase pressure can vent through the piston wall to behind the ring and press it out against the cylinder wall, increasing the effect of the scraper ring.

Now, taking that concept and applying it to a rotor. My limited understanding of how these things work, and my reading here and around, indicates that gas escape past the apex seal into the following chamber is an issue in rotary engines for several reasons.

To your knowledge, has Mazda ever tried venting the leading edge of the rotor into the apex seal groove so that the pressure of combustion gases push the seal out against the chamber wall? Seems to me that it might work, but if they haven't done it there must be a reason.

Thanks,

Pilgrim

 

The apex seals can move around ever so slightly from side to side in their grooves. At low rpm's the seals need the apex seal springs to hold them against the housings. At high rpm's, centrifugal force does it. Chamber pressures hold the apex seals towards the back of the grooves. Remember that a piston ring goes back and forth in relation to it's orientation. An apex seal is constantly trying to be pushed out of it's groove due to it's orientation in relation to movement. Fortunately the rotor housing is there so it can't. Centrifugal force holds our seals against the sealing surface. Yes the faster the engine spins, the faster the seals wear themselves and the housings. This is why we have oil injected into the engine. It's to lubricate these surfaces.

Ceramic apex seals are not as hard on rotor housings for 2 reasons. The first is that they are naturally very slippery and don't absolutely need as much lubrication to move freely. This is less friction. The other reason is that they are lighter. At high rpm's, they don't exert as much force on the housings but they still seal as well if not better. So how can they seal better if they are lighter? At high rpm's, apex seals may chatter due to improper lubrication. This is when they in essense skip repeatedly over the surface. This leaks some pressure but also will eventually wear ridges in the housing. The ceramics don't do this. The more time they are on the surface, the better they seal.

 

Question, if the apex seals may clatter at high rpms, could that be a possible reason for the marbles in a can sound of some of the members here? I'm not saying it is, but is it possible or does it not sound like that?

 

You can't hear it.

 

Thanks, RG; great info.

New question: If I knew how to calculate the circumference of an epitrochoid I could figure out the answer, but I don't, so - any idea what the rotor speed (equivalent to piston speed) is at 9k RPMs? That's just about THE major factor in cylinder survival in a piston engine. Is it so in a rotary?

Pilgrim

 

Just placed my order for the book as well.

 

The rotors spin at 1/3 the speed of the eccentric shaft. Their speed does not remain constant though. The rotors depending on where they are in the housings, speed up and slow down in relation to the housings. Apex seal speed across the housing surfaces is not constant.

Survival of a rotary is dependent on 2 main things. The first is bearing life. The engine only has 2 bearings supporting the eccentric shaft front to back. The intermediate housing does not have a bearing for support. At high rpm's this can lead to eccentric shaft flex. That takes us to our second problem.

If the eccentric shaft flexes too much, the rotors can physically come into contact with the side housings, damaging them. Race motors usually run more side clearance to help reduce this risk. Fortunately there is something that can be done which takes care of both issues at the same time.

Add a center bearing. Guru Racing out of New Zealand (I think?) makes custom eccentric shafts and can install a center bearing in the engine. This reduces flex on the eccentric shaft but also adds another bearing which gives you 50% more total area than stock. This one mod alone can do wonders for engine life at higher rpm's, including helping it to make more power.

 

Why dont Mazda put this in ? Due to cost concerns ?

 

That would be my guess. The engine already revs as high as they need it to and seems to live just fine. They would also need to make a 2 piece eccentric shaft. If you really want to push the engine hard, it's a great thing to do. Even the 20b lacks a bearing on 1 of the intermediate housings (the thin one).

 

Taken from the LMP2 thread, I thought this would be a more appropriate thread for this. Ceramicseal replied to the 17:1 comp.ratio in the porsche spyder V8

Kinda off topic, I know its stated that rotaries wont gain any more power with increasing compression ratio. Does anyone know the reason behind, or explain it in not too complicated terms?

The results were obtained (obviously) by tests conducted, but that does not state the reason. Also is there any way to fix it? Lets say would direct injection give light to raising the comp.ratio for more power?

I know I've been relating a lot of things to direct injection, however I believe that DI will give a lot more benefit to the rotary engine than we might think. Not just the gains from DI itself, ie, a little better power + emissions, I think it could lead to some major changes in the design of the rotary engine.
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