globi

Of course the Renesis has valves - again I'm not talking about poppet valves. Or how can it control the inlet flow to the different inlet ports at different rpms?
The movable things in the intake manifold are valves by definition: http://www.answers.com/valve

rotarygod

The intake manifold is not the engine. The Renesis engine has no valves. You are talking about flow to the intake runners not through the ports. This is different and has no effect on whether an engine would be better with more rotors or not. Look at the multiple length intake manifolds in a V8 Mercedes sometime or even the new 3 stage Audi intakes. Adding 1 more hole in a "valve" isn't an issue.

globi

I was just referring to the valves because of the added costs. Regarding the costs it doesn't really matter whether its part of the engine or not.

jird20

...and to continue with this topic of the "new" renesis 1.5l DI:

Compression ratio currently is 10.0:1 on the production renesis. Yes, might be still a bit early to say that the new apex seals will no suffer prematurely from the extra stress of going from 9.7 (latest RX7) to 10.0, but...

I personally think that higher compression ratio (about 10.4:1) will be well possible. Combining this to DI can result in better fuel economy (due to DI+Higher comp. ratio)+ slightly better low end torque (due to DI + HCR), and more high end power (due to HCR).

I guess the renesis DI that already moves the senku has higher compression ratio. What do you guys think (guess)?

Cheers

jird20

rotarygod

Actually it doesn't matter if you have 9:1 or 11:1 compression on a rotary. Within that range power strangely enough stays the same. Why Mazda changes it is beyond me. If you go above or below this range, power falls off.

There is no 1.5 liter Renesis and there won't be. It's all just speculation on one old members part that did not come from a magazine or any Mazda engineer. The whole point was to discuss how to do it if it were going to be done. The direct injection part we will definitely see at some point in the future. They've been working on it for 20+ years now. It's got to be getting close to finally being able to hit production engines.

As a little rotary history, the first attempt by Mazda at direct injection in a rotary was in the 70's! The engine was carburated but also had a fuel injector in each rotor housing that sprayed fuel into a subchamber that the leading spark plug also fired into. The injector would squirt into this and get ignited by the plug. This burning mixture would propagate into the combustion chamber and react with the air/ fuel mixture from the carb igniting it. This resulted in less fuel being needed from the carb. Very weird way of doing it and done earlier than anyone else. DI is nothing new in the rotary. Seeing it in production will be.

tuj

RG: why do you think that the current rotor housings will support no more port area, and why do you feel that the existing port area is inadequate to support a 1.5L?

rotarygod

I'd really have to show you why you aren't going to get any more port area. You are physically limited in space. You can't open the ports earlier as the corner seals would drop in. You can't make the ports larger towards the inside as this is where the oil control rings are. On the intake you can't go down (exhaust up) as this is where the side seal tracks intersect and the chamber is blocked by thr rotor. That only leaves us going up on the intake and down on the exhaust for any more area. This is a problem as this is changing the closing timing of the intake and opening timing of the exhaust and that messes with the powerband. The intake ports already close at 80 degrees which is as much as you want to go without messing anything up. The intake is really as large as it can possibly get. They have hit the max. We are not going to see a peripheral intake port as this is worse on emissions and manufacturers do care about how their engines test everywhere and not on ly at one of 2 load points that the current tests look at. The exhuast ports can only open earlier. This is all that can be done to make them larger. This again changes the timing which changes the powerband. It may be beneficial to open them a little bit earlier but going too large isn't good for timing reasons. People can claim the engineers will find a way to increase it somehow but there are only 2 ways to do it. I list those below.

A side port engine port area is not affected at all by rotor width changes. The side area doesn't change and the ports are already about as large as they can already get. In the past engines when they'd widen the rotors, they were also widening the exhaust ports which were peripheral. They got physically larger without affecting their timing. Yes the intake ports could still only get so large but back then they weren't nearly as large as they could have been or are now so they did have room to grow a bit. There just comes a point where you will have already found the optimum width per rotor and you can't pass it beneficially.

There are 2 ways to make a 1.5L rotary and give it the extra port area needed to breathe properly. The first is to add a rotor. 50% more side area is 50% more room for intake and exhaust ports. The other way is to change the dimensions of the rotary altogether. Make the rotary wider and taller but keep the overall proportions the same. This way you could get more side area. This method would allow the port area to stay proportionate to combustion chamber size. This however would require retooling the entire manufacturing line as nothing would be compatible with the current engines. At least with the 3 rotor option the side housings could be used and the rotors and rotor housings only need to be made thinner instead of changing every dimension.

The current port area already changes with rpm's. This is what S-DAIS does. It adds port area to keep intake velocity high but balance this with breathing ability for what is needed. We know the 4 port is limited in breathing ability over the 6 port engine which is why it can't reach the higher rpm's of the 6 port. You'd max out the intake velocity and power would fall off. We know for a fact that making that engine wider with those ports would make no more power but just shift it lower in the powerband. No one would like that. The 6 port engine only adds 1 more runner and fairly small port. This is the smallest port of all of them. It has enough area to take the engine up to a max of 9500 rpm but the power peaks lower than that. Yes that is partially due to intake design but it is really a function of displacement and total airflow. Making the rotors wider with this design will only make the peak power stay the same but again be at a lower rpm. While this may not sound bad to others as you'd have a rotary that made the same power at lower rpm's and felt torquier, how many people would buy a larger rotary that doesn't make larger power numbers? Would that be worth it cost wise? People would feel ripped off. More engine and no more power? Remember people only care about peak numbers on paper rather than actual performance. If this wasn't true people wouldn't still be complaining about "missing horsepower" on the RX-8. The car does perform as it should and to do that it needs to have it's rated power. What's the problem? A dyno is obviously not trustworthy on this car as it doesn't agree with physics.

We aren't getting a 1.5L rotary anyways so we don't really need to worry about any of this.

globi

Doesn't the 6 port also have different intake timing than the 4 port or even the 13B?
And if so, why are you so sure that the port area would indeed be the problem?

For instance the BMW M3 3.2 with VVT increases 'breathing' (over 100HP/litre @ 7900 rpm) at higher rpms by solely adapting intake and exhaust timing, but the 'port areas' stay the same. And I wouldn't be surprised if the 2 intake valves of the M3 cover a smaller area per chamber than the port areas of the Renesis relative to their displacement (0.533l vs. 0.654l). Also the rotary engine has more time to 'breath' roughly 270 degrees vs. 180 degrees.

I agree, we don't need to worry about this, but it's interesting to think about it nevertheless.

s13lover

The intake duration on an Otto cycle piston engines is not 180 degrees. My intake cam on my 240sx has duration of 207 degrees. Some high performance engines are near or over 270 degrees. I'm not sure of the intake duration alone, but my friend has a motor in his Monte Carlo with a combined duration of 570 degrees (which is the max the engine builder claimed was "streetable"). On a Miller cycle engine, the intake values are left open even longer.

rotarygod

I thought I already explained why more than once in this thread? I need to draw a picture or make a video or something.

ps1726

Will it be posible to combine both side and peripheral ports in a rotary engine, maybe using the peripherals as some kind of oversized auxiliary ports with valves
to improve airflow.

therm8

Nah, port timing would go to hell.

globi

Actually the 6 port has of course a different port timing than the 4 port.
Saying the port area is an issue can only be held as an argument if the port timing was the same, however this is not the case.
If you could show us a 4 port Renesis where port timing was kept exactly the same and only port area was increased and with it its power, I would believe your argument about port area being an issue. (A picture or video is not necessary, but feel free.)

I believe it would be, but again is port area indeed an issue?
Currently only intake port timing is controlled. I could imagine it might make a difference if one could control exhaust port timing as well. But controlling hot causes at high pressure is obviously way more difficult. (After all it works with powerful and fast spinning piston engines.)

You're right. But I also think that some rotaries have more than 270 degrees intake duration. I guess that I should have said that the piston does a 'sucking-motion' during 180 degrees and the rotor does a 'sucking-motion' during 270 degrees. You can't argue that or can you?

tuj

How is this any different than Honda's move from the F20C to the F22C? They added 0.2L, and lost some redline, but retained the same power and a bit more torque. Some people say its lost its charm, but in terms of efficiency, if you can make the same torque and power at a lower rpm by increasing displacement, and there is no major penalty for increasing it (like in America, no extra tax on cars over 2L), its a good thing. Mazda gets to take their 'high-strung' 9k engine down to 7k and retain the same power; why wouldn't they consider it? It would be an excellent engine in a fwd rotary car, or even in the RX-8.

therm8

Seems to me the moving mass of a 2.2L 4cyl engine is only slightly higher than that of a 2.0L 4cyl, while the moving mass of a 1.5L rotary is much higher (relatively speaking) than that of the 1.3L. When you consider the 1.3L takes 10% more air to make the same horsepower of the equivalent piston engine, and how much less efficient the 1.5L would be due to mass, flame propogation, etc, I doubt the tradeoffs are comparable. A 1.5L 3 rotor would be sweet, more torque, similar redline, probably more efficient...but that would entail significant $$ for retooling the assembly plants. Without more viable rotary platforms I don't see either happening. The 13B-xx has been around long enough for me to believe that Mazda will stick with it.

globi

The S2000 2.2 has an increased stroke. If you increase stroke you increase piston speed which is usually the limiting factor. If they had increased the bore, they probably could have kept the original redline and increased power as well, but needed to redesign a lot more and lost some efficiency. (Increasing bore leads to an increased surface to volume ratio and more frictional area.)

One could say that it's even surprising that Mazda took the risk to continue with the rotary engine, if you look at an engine as it was simply a black box to propel a car a rotary engine is difficult to sell to a bunch of financial people. (After all car companies are run by financial people and not engineers).

Also and again with 3 rotors you increase:
* frictional losses by almost 50%
* increase heat losses by almost 50%
* but you improve fuel distribution
* If the diameter stays the same so does the flame propagation
If 3 rotors have a higher efficiency this automatically means that fuel distribution is so much better with 3 rotors that it could offset its much higher heat and frictional losses. Very hard to believe.

ps1726

Why?, if the position of the peripheral and side ports remains trhe same in relation to the rotor travel in the housing then timing will be the same for both ports, but intake, and exhaust area will actually be the sum of both ports areas. And if you are able to close the peripherals at will , them you can vary the volume entering and or exiting the trochoid chamber. Think about, its plain geometry, that way you can increase port area w/o changing timing.

globi

Actually there is less overlap with side ports.
http://www.der-wankelmotor.de/Techni...k_auslass.html

Of course if you could close the peripheral ports at will then you could use the advantages of both (side and peripheral ports). But whether the potential power increase justifies the added complexity is an another question.

rotary crazy

the problem with peripheral is emissions, but if mazda finds a way theres a lot of power to have fron this type of system.

therm8

well I don't think diameter needs to stay the same. 10A sized rotors would work. The engine could be shorter (height) and skinnier, but longer (length). From my understanding, most of the friction is centered around the e-shaft bearings, and since the shaft is spinning at the same rate, but has some added weight, I don't see this increasing friction by 50%. Windage losses would increase. At the very least you could get efficiency equal to the 13b, I would think. Heat loss would increase, but only in proportion to power output, so it's effect on efficiency would ideally be negligible, but in reality would have a slight negative effect.

I'm just speculating on most of this stuff, because the rotary, though being an ICE doesn't behave quite normally, and I'm nowhere near being an expert on this stuff.

jird20

My wish about a possible 15b DI :

1) DI, of course
2) 3 rotors
3) Number 2 implies 3 rotors with the same "front view" as the rotors of a 13 b-MSP, but with a depth of just a 76%.
4) As inlet as exhaust ports areas remain identical as per a 13b-MSP breathability would be increased in a 31%
5) Number 4 could lead in a higher redline, may be about 10-10.5 k rpm (here mechanical issues probably would limit the max. speed)
6) Compression ratio of 10.3-10.5
7) One disconnectable rotor (retractable apex seals), to improve fuel economy a partial/low loads

I can even hear the smoothness of such an engine...

I hope to see some of these features in the next RENESIS II

Cheers

jird20

tuj

you're nuts.

zoom44

um you could just not inject fuel into that rotor

tuj

besides, stratified charge DI is more efficient than DOD

globi

When you'd use 10A sized rotors versus 15A sized rotors, rotor-diameter would stay the same.
If you use three 10A vs two 15 rotors you need two additional walls which will make the engine longer at the same diameter.
The e-shaft bearings are running on an oil film and don't need to seal against high gas pressure. Therefore my guess would be that the e-shaft doesn't deal with that much friction and most friction appears where the rotors have to seal the combustion chamber.
If heatlosses increase with powerinput that means heatloss is always a percentage of the powerinput. Heatloss is powerloss and powerloss is efficiency loss.