Mr BiG G

ohhhh....but is the expansion rate and what not ok for the material used to make rotors to be titanium? and what else can rotors be made of?

Mr BiG G

and what if instead of having one dimple on a rotor....have 2 dimples....wouldn't that help with the burn rate?

pinkfloyd

burn rate. easy to chang
1. octane gas
2. it has been said that we would use 4 spark plugs so it would work.
3. i am not understaning what is being asked and am wrong

QuagmireMan

hmmmm

chairchild

That was the original plan

But I agree, two rotors welded together woulnt be very good for strength - so an entirely new rotor would have to be machined. Well, if someone's going to ACTUALY make this (who has several $$$$ spare?) they might as well make the housings and end-plates as well, and have their own design rotors

But QuagmireMan, how does the rotor "know" which way to turn in your engine? Or how does a piston "know" which way to move? It was already set in motion by the starter-motor, and kept moving in that direction by the flywheel. The only problem with going this large, would be the fact that it would be EXTREMELY slow to increase the revs. So I agree that it would probably be best to have it run on diesel

It would be the complete opposite of any other rotary - slow revving, low redline, and shedloads of torque!!!

Mr BiG G

pipe dreams chairchild pipe dreams.....unless one of us wins some lottery

pinkfloyd

we are still doing a two 2 rotors. thats confusing. i mean we are doing 2 big rotors....not just one big one. because as stated before just one big rotor would unbalace everything, so to big would cacle each other out. right.........or at least make is smoother.
Can anyone take a gusse on what the max rev would be. i say like 7 at the most. if built right. and if someone acutally dose this i bet he will have enough money to do it right.

Mr BiG G

yea i guess 7 would be about right....but i guess if u went titanium rotors or sumtin....if u have that much money....then ur rpm's will prolly be way higher than 7 grand

pinkfloyd

i still do not understand how two dimples is better then one big one. i am still in highschool so i have not taken any ME classes. I bet if i did i would understand a little better.

Mr BiG G

nah u dont need no classes....when u have 2 dimples u have 2 spots where u can make power i dont really know how that would help but i feel it does cuz it also has like a 2 cylinder in 1 kinda thing which has 2 small pieces of fuel burn areas which burns the fuel better

pinkfloyd

i would like to make a name for this thing so we can Refer to it easily. something simple like, 2+2. anywas wouldend this 2+2 be about the same size as a 20B. Although it would creat more power becuase in the end it is bigger it would also have a lower rev limit( even if you said you used titanium rotors it not a fair compareson to a 20B becasue a 20B dose not have titanium rotors and if it did it would have a higher rev limit then a 2+2. and the cost of this would be more then a 4 rotor, witch might i add is cheeper. although this is very cool and neet. not really all that better.

chairchild

The reason for having two dimples is because it will still be based on a standard rotor. If you think of a 13b, it has two dimples. But if you made the dimples bigger (same effect as one big dimple on a 2+2) then you lose compression, and hence, you lose power.

But having multiple places for making power, will increase torque more effieciently than having one huge dimple.

Think of it this way. If you hit a rotor with a big hammer to get it to turn, you would need a fair bit of guts to get it to go with any power. But if you used two small hammers instead - you would still need the same amount of power, but it would be less stressed

less stress = more effieciency

pinkfloyd

cool. thanks i understand now. but then why not do 3 dimples or 4 or whatever.
something else i would like to add. can anyone give an Accurate length of this engine. Also how long would it be if we did 3-2 rotors. Because you don’t have the plate separating each rotor I think a 3+2 would be the same size as a 4 rotor.

I love dream world dont you?

QuagmireMan

i think the dimple thing is for more surface area and to control hot spots, but not til i complete my classes could i tell you for sure...

Kenku

All righty, let's go over as many of these points as I see.

First off, rotors are comparatively simple. Housings aren't; the Mazda housings are made by taking a strip of steel, flattening it around a form in the right shape, casting the aluminum around it, hard chroming all of the inside... they're not really something that can be easily machined. End plates sure; I know you can make those on a milling machine. Willing to bet you could custom mill rotors too without too much trouble. But housings... not... really.

Secondly, the rotor "knows" which way to turn because of the ports. If the starter were to turn backwards, it would push fuel and air out the intake, suck air in through the exhaust and not run. Piston engines "know" which way to turn because of cam timing, which accomplishes the exact same thing.

Titanium rotors aren't impractical due to expansion, they're impractical due to galling characteristics; the sliding apex seals (to say nothing of possibly touching anything else) would fairly rapidly screw stuff up. See a post on someone trying titanium apex seals for examples of that. There are *NOT* Titanium pistons.

Now. The dimple thing. The dimple is there to reduce compression and get the flame front moving in such a way that it works a little bit more efficiently. There's no real reason why having two dimples is going to work more efficiently than one and some reasons why it won't. Two dimples is going to mean a greater surface area, which means that there's more area of the rotor absorbing heat, which means that that heat isn't doing any work turning the motor.



Now. Here's the question for all of you. Can anyone tell me any single thing that 2 double width rotors gets you as opposed to 4 single width rotors? Aside from problems with the flame front having to move massive distances, really long apex seals, and a lot of necessecary work to dynamicially balance it, I mean. Here's a hint: the displacement is the same either way. The engine is moving the same amount of fuel and air in and out of the engine per revolution of the eccentric shaft either way. The only difference is that you get to have even *MORE* problems with combustion efficiency than normal, and let's face it, rotaries have enough problems with that as is.

pinkfloyd

true. i say we start talking about the best way to make a 4 rotor twin turbo with super charger. it is possible. i just want to konw the best way to do it. but i know people will say just rig up a 20b because with a 4 rotor twint turbo with super charger would creat so much power that it would not be practical. also riging up a 20 is a lot cheeper. but this whole thread is a dream anyway.

Kenku

Enh, why bother with a supercharger? 4-rotor will get you enough displacement where lag's a non-issue, and personally I'm not too enamoured with the things.

Screw 20Bs. Eccentric shaft flex and various other issues.

Dunno, you say this is a dream, but I'm sectioning end plates as soon as I get a 3-phase power converter for my milling machine. I'm pretty damn sure I know how they look internally, and if I'm right, there's nothing to stop me from going and making my own intermediate plates. And after that, it's just a matter of a custom eccentric shaft which... is an issue, but one that I think I have figured out too. Not sure if I could make that one, but I know people who can...

pinkfloyd

you say flex with the E shaft is a problem in 20B's tha that means it would be an even great problem in a 4 rotor....and i agree with you on the super charger. I never really thought about it. and i was never a big fan of the super charger, i was just thinking that all rotorys suck down low.
I am still new to the internals of the rotory but why dose the e shaft flex so much. dont the plates In-between the rotors have baring or something for the e shaft to rest on and keep it form flexing.

Shamrock.James

I'v been looking at rotaries with a great interest over the last coulple of weeks and will tryu and pick up a 13b to make a test bed out of soon.

There are two main problems that plague rotaries:

A: they don't burn thier fuel efficiently enough, everyone knows they guzzle like a little bitch, this is the first problem that needs to be resolved, i'm thinking smaller rotor/ injector size, you need to burn all of that fuel effiently for an engine to be sucessful

B: Rotors' ports are like the cams on a car, they are set to give a specific peak of performance in a certain rev-range, now i belive a rotor really need variable Pheriphal Port move ment, like a pheriphal port that can move up and down, according to engine RPM so that the enigine can have low and top end..

This could also be done with stock porting and a pheriphal port that could open and close at a specific rev-range ... like V-tec.

As for Apex seals, i have seen a new method of drilling a hole through the middle of the rotor from the apex, and fitting of a custom made seal spring and stoper valve, this allows the apex sping to be lubricated by the engine oil...

Also Rotaries, are destroyed by detonation, just like cylinders are, but would it be posible to set a high tension type blow-off valve into the side of the housing, so that if detonation did occur, the preasure would be greater that what should be expected in that area of the housing chamber and therfore expeling the gases from the vlave meaning if set up right you techinally couldn't kill you engine from detonation, meaning you could lean right out and so reduce fuel consumption...

Well anyway they are just a few ideas i have had.

Kenku

No, actually, it doesn't mean it's a bigger problem with the 4-rotors.

The reason shaft flex gets to be an issue for the 20Bs is the layout of the rotors... stationary gear, rotor, stationary gear, rotor, rotor, stationary gear. What happens is that there's an intermediate plate with no support, which works okay in 2-rotors. With the 3 rotors though, the lobes on the e-shaft are 120 degrees apart... which means that the bit with an unsupported intermediate shaft is unbalanced even though the entire rotating assembly as a whole is. If you were to put a needle bearing on that one intermediate plate to support it (like Guru does with their custom 2-rotor e-shaft) the problem would go away.

The 4-rotors have what's essentially a 2-rotor e-shaft in the middle; rotors 180 degrees apart. The rotors on either end of that are 90 degrees away from the inner two lobes. This works because the stationary gears support the shaft on either side of the two end rotors, so it's not going to be flexing anywhere.

That all took be a bit of thinking to figure out the first time I had to explain why the 20Bs had problems here and there at high RPM.

Interesting thoughts. I'll go at 'em one by one.

Your first point, that the shape of the rotor introduces combustion inefficiencies, is the original point of this thread. There's not really much getting around that. Smaller injectors aren't a solution though; the engine needs to have enough fuel to maintain proper air/fuel ratios.

The second point, of variable port timing, is approached in a different way. First off, know that the NA 13Bs from the RX-7 onwards have variable port timing of sorts; a 5th and 6th intake port that have more duration and area than the initial ports. Peripheral ports moving around like you suggested would be very hard; the issue is that timing relies on the seals running over the port, and thus moving the port would mean having something that seals perfectly flush to the inside surface of the housing. Also, peripheral ports work inefficiently at low load levels (fuel economy problems at idle and stuff, IOW) so side ports have a pretty good place on street engines. Your idea of having peripheral ports that are valved open at high RPM is a good one though, but not a new one. Mazda was playing around with it back in the early days of their work with rotaries, and various other people have thought of it.

The idea of drilling an oil passage to get engine oil to the apex seals is an interesting one. I have to wonder if that would lead to oil starvation issues on the rotor bearings though...

The quasi-blowoff valve idea is an interesting one, but I don't see it as being very practical. The problem is chamber pressures; at the pressures involved it would be difficult to have a valve that would discriminate between normal combustion pressures and detonation overpressure... and even given that, the shock wave speed is such that it's likely that it would break apex seals and whatnot before the valve could have a chance to open. Not really a bad idea, just impractical to make.

QuagmireMan

i dont know how it got to be this way, but originally the idea was smaller is better, your able to control it more

Kenku

It got to be this way because someone threw out the idea of bigger rotors

FWIW, one of the major sources of combustion inefficiency is quench; the trailing side of the rotor snuffs out flame and thus there's a little layer of unburned hydrocarbons. The trailing plug helps that a bit, but it's still an issue. Late trailing, as on the LeMans motor, would help a bit more. The renesis gets around this (emissions-wise) by having it so the layer of unburned hydrocarbons just keeps going around; the exhaust gas flows out the exhaust ports, but centrifugal force keeps the quenched layer around for another go at burning it.

t-von

iTrader: (8)

Answers:
1. Shorter engine with two less side plates.
2. Overall weight savings.
3. 3 moving parts.
4. Cheaper production cost(fewer parts).
5. Broader range of application.
6. Keep the same displacement with a smaller package.

As far as the burns rate and apex seal longevity goes, I'll leave that one for the experts. However, as previously stated by myself, this engine would be NA. NA rotarys have always had better emissions than turbo ones. Also NA rotary apex seals last longer as well. We could also further help emissions by widening the side plates to incorporate larger side exhaust ports like the Renesis. Now the engine will have zero overlap. This could also help the apex seals.


I don't understand why everyone seems to think the engine wouldn't rev high. The rotating mass is virtually the same. 4 rotors can rev extremely high. I also don't think the engine will be hard to balance.

The other day I went out to take some measurments. I would appear that this engine would only be 1 1/8" longer than my 20b. Hmmmmm not bad! We could also shorten the engine by doubling the 10a rotors to have a smaller displacment version.

Overall, I think that the above advantages far out weigh the negatives. Those negatives can be overcome with more R&D. Remember, Mazda actually experimented with the side exhaust ports in he past but was unsuccesfull back then with that design. Now years later that engine is gracefully in production on the road today(Renesis). Lastly this engine would have V8 like low end torque while also having the rotarys high reving capabilities. That my friends is the ****.

Kenku

All righty, here's some more factors for you.

In order to have the 2 stationary gears per rotor like you suggested, you have to have a multi-piece eccentric shaft. Which does nothing good for production cost or ease of assembly. The flame front problems and apex seal issues are the biggies against it, but you didn't address them so I won't again. And it could be said that those problems would outweigh any benefits, but, well. I'm just going to talk about some of the new things you brought up.

First of, using the Renesis style side exhaust. Well, for one thing, as you said you'd have to widen the side plates to do so. The problem is that the Renesis style exhaust is sized for an engine of half the displacement of this new thing; you can port it out to be larger, but not *THAT* much larger. It's the same problem that got pointed out with intake ports and someone proposed solving with peripheral secondaries, except for the fact that you can't really valve shut the exhaust in the same way. I don't have to point out the problems with not having enough exhaust flow, do I?

Finally, as to length... you have have noticed Mazda never put a 3-rotor in anything but the Cosmo luxury car? I don't see them making an engine even longer than that, and I don't see anyone short of Mazda having the resources to make new rotor housings.

Going down the list. Shorter engine is debateable unless you're going pure peripheral port, given the fact that the center housing has to hold two stationary gears now *AND* all the ports have to be substantially embiggened. Overall weight savings is the same. 3 moving parts is... well... I fail to see how that's much of an argument. Cheaper production costs seems unlikely when you are designing essentially the entire engine from scratch and have to make new tooling, broader range of application I have to wonder what you mean by, and same displacement in a smaller package is debateable for the same reason I brought up already. In exchange for that, you get a lot of problems making the ports flow enough air for it, and a much larger surface for even worse combustion efficiency.

pinkfloyd

i did not even bother reading the last two post. 4 sing rotors is better then the 2 big onse.