Any engine builders out there? Speculation welcome, but at least try to make it SOUND reasonable.

Okay, given that Formula 1 engines run at 20,000 rpms and last for two weekends of racing.... Yes these engines are special built for this, but I was wondering:

If you took a Renesis, and decided that it only had to survive 20 hours of use:
1) What would the top RPM be ?
2) It seems that enigines top out HP/torque near red line. Is this only a function of fuel/air maxing out?
3) What would you do to make the extra rpms actually produce more power? More air/fuel? Would you also have to change the rotor/compression?
4) Ultimately, what kind of HP could you get out of the engine?

 

Depends on the gasoline mostly. Because lower octane has a lower resistance to detonation, you can't rev too high with it. Thats why race cars use like 110 octane and can rev to like 15,000 RPMs. Of course, they do rebuild their engine every time before each race. But I'm sure the rotary can go WELL past 10,000 RPMs EASY.

 

Octane rating or AFR is not related to an engine hability to rev. It's mostly related to mechanical / material limits and breathing.

Given an engine, the power will increase almost proportionnally to the rpm increase. Almost, because mechanical and pumping losses increase with engine speed.
You would have to improve air induction to the cylinder / rotor, in order to keep inducted air velocity well under Mach speed (0.6 Mach maximum if I remember correctly).
I think combustion chamber would have to be pretty small in size in order to have a really quick combustion.
They are many other parameters to consider.

Fabrice

 

Wasn't it printed/stated somewhere that the Renesis was tested up to 18,000 Rpms? I've been trying to locate that article or post for the longest time...

 

F1 cars rev to 20K + (cosworth as of late has breached the 20,000 rpm line!) and run on pump street gas.

They are required by regulation to run on the same gas you and I run. And yes, they check it after every race to make sure no one's runnign funny stuff.

NASCAR cars don't see anything over 9000 rpms because they're different -- F1 is big-bore very short stroke, NASCAR is yer typical stump puller taken to the illogical extreme

Has nothing to do with the gas, and everything to do with reciprocating mass.

 

I don't have the CAR-BRAINS to talk in this thread, lol, but how would you and what is the max potential of a NA Rotary engine (the Renesis to be more specific)?

I've heard about that company that builds 3-Rotor monsters with 400+ HP (closer to 500 if I remember right) but their Rotary has twin turbo's.

I don't need 500HP so I wonder if a NA rotary could produce 325-400HP?

 

F1 cars now have to follow the rule of one engine per 2 grand prix race weekends, with a ten-palce grid penalty for those that break the rule. You could see as as 1000 miles over the 2 weekends.

 

Your question is highly subjective.

Air-fuel ratios are a thermodynamic problem, not a mechanics problem.

The rotating mass has a certain speed at which it can produce its maximum power [remember (angular speed)(torque)=(shaft power)] before the curve eventually falls off. I wanted to say it was like compressor stall, but that's an aerodynamic problem. Making the engine spin much faster, from what I've read and seen, shifts the powerband to the right. I believe this explains why for example, a typical LS1's maximum power is at a lower speed than an S2000 engine's. Also, I believe it has something to do with displacement. This can be traced back to my example.

Remember that angular velocity is a function of the rotating mass, so therefore, use a lighter rotor if you're going to build a high-speed rotary engine. You'll lose low-end torque (Torque=Force x Distance) because you have a loss mass multiplied with a low speed. This goes back to your first question of how fast you want your engine to run. It's primarily dependent on your rotating shaft and rotating mass. Friction comes into play as well.

When it comes to making ultimate power, there are many things to consider, such as fuel enrichment, the shape of the intake runners, the shape of the exhaust, the shape of the valves or ports, whether you're considering forced induction, strength of materials, etc.

 

Here's your answer to the 300+ hp N/A rotary.

 

Rotary god gave a good explanation of this I believe. I think he stated the Renesis as is could take no more than 13k rpm's. At that point the eccentric shaft would flex too much and the rotors would begin rubbing the sidewalls. In order to get around this you needed to use a stronger eccentric shaft and add a bearing inbetween the two rotors. Stock there is only one at each end.

Also the port size largely determines where you make your power in a rotary engine. They need to be larger to make power at higher rpms and smaller to make power at lower rpms, to keep the air velocity up. This is the trade off! Similar in a piston engine. Ever seen one that barely can hold idle. It's because either its loosing compression, bad, or it's optimized to operate at a higher rpm. Not because of port size in this case though, instead because of port overlap.

Many other things as well would need to be changed to increase the redline of the renesis or any other engine. Its not a practical thing to do. Just add FI or nos if you want more power. Search for the thread by rotary god on this, it will give you an idea of what else is involved.

 

Octane is used to eliminate detonation in the combustion chamber of an engine. You use higher octane levels to Slow down the speed gasoline is burned. The higher a engine revs, the less important the octane rating of gasoline is. The use of too high of an octane gas at super-high RPM would result in still burning fuel being pushed out the exhuast. Power would be wasted. Lower octane fuel would work better in an engine at 15-20K RPM. This would be the same for a rotory or a piston engine.

 

And, if I recall, there was a discussion that if you fix the flex and breathing problems, the next limitation would be the propagation speed of the flame-front. Since the combustion zone is moving there's a point where the rotors would begin to overrun the speed at which the a/f mixture can burn. I seem to remember the ultimate theoritical speed for a renesis-sized engine was postulated at around 18K RPM. But I may well be talking out my a**.

This flame-front propagation has a bearing on the size of rotary engine you can construct (just as it does for the size pistons can be). Ingersol-Rand made a huge rotary engine for natural gas pumping that had rotors about 1 meter in diameter. It was limited to very low rpm and could only run properly on natural gas (which was particularly convenient in this application).

 

some of the mazda racercar rotaries have 3 spark plugs to help with the higher rpm's and to get some more efficiency out of it. Lemme see if I can find that picture.

yeah the 787b engine was 4 rotor 3 spark per rotor. http://www.poweraccel.co.jp/images/engine.jpg

 

This all makes sense indeed.

For info, the Ingersol-Rand was quoted at 550PS at 1000 rpm for the 41 Liter (quoted from memory) single rotor version.