So far the evolution of Mazda's rotary line has been to larger rotor widths to increase displacement, with a scattering of 3 and 4 rotor engines with identical rotor widths.

My thoughts are that the progression of the rotary engine may have to return to smaller displacement per rotor. We already know that full combustion is difficult in the long, shallow rotary flame-front. So perhaps it makes more sense to build 4 rotor inline engines or perhaps (2) 3 rotor engines side-by-side, each with narrow rotors and/or different radii and eccentricies. This certainly would seem to benefit fuel consumption and emissions. This in turn would perhaps allow a return to a perhipheral exhaust.

Finally, I'm curious if anyone has experimented by combining both side and perhiperal ports, especially using ducted runners. I suspect the availability of multi-directional airflow into the rotor could well provide signicant power increases, especially if properly resonated.

Thoughts?

 

Im not sure if doing so would actually get better fuel economy rather than making it worse. It sounds like an interesting idea. I think the weight of the engine and the cost of production would both increase though, so that might be a deterent.

 

I was pondering the exact same question this weekend.

I figure that a 1.3 - 1.5L 3-rotor would make a great engine. Higher RPM available due to smaller rotors, an increase in torque and HP due to 3 combustion cycles per crank revolution, smaller flame-front and better overall combustion.

There would be a lot of benefits. There would be higher production costs but I don't think it would be that significant.

Chris...

 

Yes. I understand the difficulties and associate costs of 3+ rotors per e-shaft (like the need for a multi-piece e-shaft, etc.). It seems to me that the eventual evolution of the engine would go in this direction.

 

a smaller 1.3 does sound good.

 

It's true that you can increase rpm with smaller rotors and you can potentially reach higher power output, but you actually decrease the efficiency of an engine by increasing the number of rotors. If you scale down the surface to volume ratio goes up (no matter what shape you start with), which means the hot gases have more surface available to cool down and lose pressure and therefore torque. However with smaller rotors you might get better air fuel mixing but will this be enough to offset the loss caused by the higher surface to volume ratio?
Also with more rotors (or cylinders for that matter) total friction goes up if total displacement stays the same.

Btw the surface to volume ratio plays also an important role in aerodynamics or friction in general:
Have you ever wondered why sand can fly and a rock can't even though they share the same density? It's because the surface to volume ratio is so much larger that wind can cause enough lift, to carry it away. For the same surface to volume ratio a bumble bee can lift off with much smaller wings than an eagle can (comparitively speaking) or an Airbus 380 is inherently more efficient than a Boeing 737 or a big rig is more efficient than a car.

 

Actually, raising the surface to volume ratio would probably help power because it would increase the thermal efficiency of the engine. Since there is no cooling stroke, the rotary is already somewhat thermodynamically inefficient.

 

Raising the surface to volume ratio will reduce thermal efficiency of an engine.

Here's the 4 cycle engine explained (the rotary is thermodynamically pretty much the same) and you want to reduce heat loss during the expansion stroke as much as possible. (However increasing the surface to volume ratio will do the opposite.)
http://techni.tachemie.uni-leipzig.d...to_g0_eng.html

Also there's a reason why this engine has a thermal efficiency of 50%.
http://www.bath.ac.uk/~ccsshb/12cyl/

 

^^^ holy ****, 5.6 Million lb-ft/tq good lawd!

 

In theory, I buy that increasing the surface to volume ratio decreases the thermal efficiency. But I think there may be advantages to increasing the ratio that will reduce the amount of heat absorbed by the engine, namely easier cooling.

 

That's true there are advantages as higher rpm and cooling is indeed improved not only because the surface to volume ratio is larger. It's also improved because the heat doesn't need not travel that far anymore since the parts are also smaller (e.g. better rotor cooling).
For some time there were V8 competing against V10 in F1. The V8 had the advantage that it generally had lower fuel consumption and the V10 had the advantage that it could reach a higher rpm and therefore produce more power.

 

i want to put the strokes of the cycles on opposite sides of the rotors. i.e the front would have its intake and exhaust as it is now and the rear would have them on the opposite side. this would allow for a full size seperate center exhaust port for each side instead of the siamesed port. then you could have a proper header and increase power output. i wonder if this would also help cooling since the heat would be mor eevenly distributed rather than concentrated on one area?

 

Actually I'd want 2 peripheral ports with valves (in addition to the side exhaust ports). The valves would open at high loads and rpms to improve scavenging and close at low rpms to improve partial load efficiency and emissions.

 

I don't think there is any reason that the center exhaust has to be siamesed. They could always just make the center housing a bit thicker. I also wonder why no one has tried to design a header that keeps the two center exhaust ports seperated until farther down the line?

I agree with globi that the peripheral port intake and exahaust ports would be awesome, especially controlled by actuators.

 

For street use I don't see any reason why not to keep all side ports. Emissions will get worse with peripheral exhaust ports and the total exhaust port area per rotor is alot less with peripheral exhaust. I'd keep them all side. That was the single biggest advancement that made the Renesis possible. Why would anyone undo that? It's a step backwards. Race use is another story.

I'd like to see a 3 rotor engine with smaller rotors with a total engine size the same as the current engine or possibly even slightly larger at 1.5L. By keeping the all side port configuration you can keep the same total port area as a larger chamber which gives you more flexibility with port timing and auxiliary ports. A peripheral port exhaust is very limited in size as it can only go so wide and going up or down alters the timing. I'd also make sure that all of the rotors had their own dedicated exhaust ports. No siamesed runners. I'd also run the engine direct injected as well as running negative timing split for emissions and low speed/load power. The 3 rotor setup would make the engine as smooth as a nice 12 cylinder engine and give it a very nice sound.

I'd make all of the housings out of aluminum for lightness with a replaceable friction surface for the side an intermediate housings. Like these:

http://www.rotaryeng.net/two-piece-end-house.jpg
http://www.rotaryeng.net/2pc-end-house.gif

I'd also use a 3 piece eccentric shaft that allowed the use of a bearing in each intermediate housing which would give us full support and allow less stress per bearing. That's just how I'd do one.

 

Actually I wouldn't stir away from side intake and exhaust ports either.

I would just add a peripheral exhaust port in addtion to the side exhaust ports because this would allow variable exhaust port timing. (There is variable intake port timing already.) It would only open at high loads and rpms and therefore not affect emissions at a normal driving cycle.
I wouldn't valve side exhaust ports because it'd be more challenging than valving peripheral ports.

Not quite on topic; but I just noticed that fish sticks are smaller than they used to be. Scaling down increases the surface to volume ratio (as always). If you make smaller fish sticks, you can sell more total mass of fish sticks by using the same amount of fish.

 

youre suck geeks :p

 

RG: I agree that the side ports are a great advancement, but I believe you've said yourself that peripheral port is the way to go for big race power. I'd hate to have to introduce something like a door/valve to keep the p-ports closed, but wouldn't it be worth it for ultimate top-end power?

AFAIK, most emissions tests are done at lower rpms, light load or idle, so activating the peripherals at the high part of the band shouldn't affect emissions tests.

Now what about the current center exhaust? Why hasn't someone tried dividing the center runner to make a true tri-y design? Exhaust theory says that there should be some gains if it could be done.

 

they have. ive seen racing beats version so has RG

 

So what are the results? Is the siamesed port actually a benefit? Since this is an all-new motor in an all new vehicle, I'd be quite surprised if the siamesed center port was result of cost or packaging constraints.