Renesis Exhaust

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Vigilant1

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My 12A Datsun 1000 Coupe (Sunny B10) was pretty wicked!
Fun, Fun. You about doubled (more?) the HP with that engine swap. Kept stock-ish looking, that could produce some fun moments when the traffic light changes, esp as the RPMs go up an she keeps pulling way. A "sleeper" indeed.
 

Peterson

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20160122_061819.jpg

My not so elaborate rendering of what I was talking about.

The annular ambient air exit/ second stage silencer has a cross section area of 12.56 in sq. If the whole exhaust was shrouded in a mix of ceramic and s-glass, a scoop with an entrance area of 14-15 in square could keep cooling air flowing through at higher velocity and keep under cowling temps lower.

Not exactly to scale, and done freehand, really just enough to get into design phase.
 

Himat

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Internal combustion engine muffler acoustics is not what I am well into. Anyway some points to check:
- To look at it as free space is probably wrong. This case look much more like tuned cavity resonators.
- Wave propagation and mass flow must both be cosidered.
- Any abrupt change in pipe cross section is an impedance change that will reflect part of the acoustic wave.
More to follow when i get in front of a PC. Tablets are best for reading...
 

Vigilant1

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View attachment 46742
My not so elaborate rendering of what I was talking about.
Interesting. Two offerings:
1) Creating the destructive interference. Unlike a conventional sound system in which the sound pressure waves are moving in a static medium, in this exhaust system the medium will be moving in the same direction as the pulses, and the speed of this medium is not insignificant. I'm sure that's all taken into account in your calculations, but it would seem to my caveman mind that a) this complicates the design somewhat and b) changes of RPM and throttle setting would change >both< the speed of the gasses overall and the time between opening of the front rotor exhaust ports and the rear rotor exhaust port. So, potentially not a simple problem and it might only work at certain RPMs. If the interference is destructive at 6000 RPM but constructive at 5500 RPM, it might not make the neighbors happy.

2) Cooling: I wonder if something could be done to directly address radiant heat from the big can (which affects everything else under the cowl and the cowl itself), and also to get some cooling air under dynamic pressure (rather than just the ambient undercowl higher pressure) to work on this. Perhaps a 7" dia lightweight outer jacket around the can fed by a small blast tube, the jacket tapers down to feed your present second stage silencer jacket. You'll need some sort of heat shield around the stuff regardless, I suppose the question is whether it's worth the trouble of sealing it up and providing dedicated ambient ram air. It would make a dandy heat muff for carb or cabin heat.
 

Peterson

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It's still in the drawing board phase. Still need to source a salvage Ren and som 321 stainless tubing to build a prototype. 304 is readily available but 321 handles heat better. 625 inconel is too rich for my blood.

On paper, it should work over a wide RPM range, but can't tell until physically able to test. Second stage deadening via annular cooling air will most likely work better at cruising speed than taxi, but this does allow the use of tune length runners with marginal increase in physical size.

Vigilant's response has me wondering if designing destructive interference similar to a stationary sound system will cause good cancellation in the cabin, but end up louder on the ground due to Doppler effect (?) as the craft moves at a rate of speed that causes constructive interference. Huh
 

rv7charlie

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I'm installing a Renesis on an RV-7, & I know quite a few guys who've been flying 13B, 20B & Renesis a/c for years. Some thoughts from observing them, and watching rotaries since my father bought an RX-4 back in the early '70's:

Quality 12A parts are getting harder to find, and unless you do major performance mods (not advisable for the inexperienced), they will do well to make 150 HP. Weight isn't likely to be any less than a Renesis.

When the Renesis arrived, one of the performance shops tried every exhaust tuning mod they could imagine, & gained ~7 hp over the stock (restrictive) exhaust. With side intake & exhaust ports, the Renesis has no overlap, so exhaust tuning doesn't help. Only backpressure reduction is effective on the exhaust side.

While exhaust tuning does almost nothing on the Renesis, intake tuning becomes even more critical. Some of the guys I know had really lousy performance until they got the intake right.

As Ross hinted, any muffler 'packing' will be 'no packing' within a few hours. Or if it's structurally strong, it can become 'plugging' at any point, as happened to the Mistral test a/c. I know quite a few guys who've been flying a lot of hours, & all that I know have some variation of a straight-through exhaust system without 'baffles'. Some had 'packing', but it's all gone now.

Cooling the exhaust is going to take a LOT of air (cooling drag). And it's likely to completely kill the small but measurable thrust it's capable of providing at altitude. And, it's still going to be tough to avoid radiant heat transfer, unless radiant barriers are used (which basically solve the heat problem).

While the Renesis isn't quiet, it's a lot less offensive than the 13B & 12A. The 'hard right' that's forced by the side exhaust ports seems to scrub off a lot of the high frequency harmonics in the sound. Below is a shot of the quietest rotary I've ever heard. It uses a cut-down stock exhaust manifold feeding what amounts to a swirl pot, which then feeds a very basic muffler. This plane actually sounds a little like a gutsy turbine, with the prop making more noise than the engine. This plane flies with his neighbor's Lyc 180 HP RV; same speeds and same fuel burn.

100_1445 (Small).JPG

Forgot to add, the quietest 13B in an a/c I've ever heard was in an SQ2000 pusher. He was using the stock cast iron manifold (~15 lbs) which fed a very short, straight tube pointed aft. I never got to see it fly, but I did see some high speed taxi work. As strange as this seems, it actually sounded like an unmuffled small block V8. Very pleasing and unlike any other rotary I'd heard. Mazda has obviously done its homework on their automotive exhaust manifolds for rotaries. The Renesis manifold (pic above) is a really complicated piece of hardware, with 3 layers of different metals, tabs welded in strategic spots that attach to nothing, etc.

Charlie
 
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Himat

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As old as this thread is, i have a contribution for a Renesis exhaust system. The front and rear rotors each have a side port exiting on the front and rear iron respectively, and a shared exhaust port in the center iron. A tangential muffler has inlets on the side of a round chamber with the outlet exiting from the end.

The idea is that pressure waves from the exhaust pulses swirl around colliding out of phase, significantly reducing the volume of the exhaust blast. The Renesis, with it's dual exhaust ports per rotor, (center port Siamesed between both rotors) the exhaust runners can be tuned to their short length for the engine RPM (plenty of apps to calculate this) can be wrapped around the cylindrical chamber in opposite directions. They can enter the chamber on the same plane, ensuring that pressure waves collide out of phase every time.
If I understand you right, you do think to make something like I have tried to draw here:
RenisisExhaust.jpg
I have "flattened" the inlet pipes from the engine, and to show how they enter the main chamber from different sides.

I do not think this is a good idea, as the exhaust flow then get restricted by the different inlets to push for swirl in different directions. If all where to enter the same direction, a better flow may be obtained.

Acoustic I would think the difference would not matter. The abrupt cross section change as the tubes enters the main chamber result in an impedance difference where part of the sound wave is reflected back to the engine. The other part will enter the chamber, but depending on the wavelength as a point source where direction is unimportant. This will excite some sort of standing wave pattern, or call it resonance, within the main camber that again will couple back to the inlet pipes. The thing to avoid is then resonances that travel back the inlet pipes and restricts the exhaust from leaving the engine or the exhaust to leave the inlet pipes. For sound silencing, the main chamber should have a size so that the loudest frequency can not persist in the volume.
 
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Billrsv4

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Renesis Design is specifically to deal with CAR issues. Torque, smog, and noise. There are some advantages, the exhaust is cooler than the 13B, but that in turn requires more heat exchanger to keep the engine cool. ((the heat goes into the water) Reports are from "just a bit" to 8%. You need the freest flowing exhaust you can manage. I've seen theoretical systems that really didn't work well and others that should suck that make good power. A good long primary tube helps. I'd build your Renesis like it was a 3 cylinder piston engine. Put good long primary tubes on it. All 3 outlets. Length depends on the RPMs you want to limit it to. The Renesis cooler exhaust means you have more choice of commercial mufflers, but avoid glass packs, keep it all metal. The wicked sonic pulses still reek havoc with mat type mufflers. If you want the most power in the smallest package stay with the 13B and go P-Port.
Bill
 

Will Aldridge

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I'd like you guys opinion on my exhaust design for my aircraft. From what I've read the short runners may hurt me performance wise but I still think with a significant hp loss to the exhaust system I'll still have plenty of power for a small slippery single seater.

exhaust headers.jpg
as you can see in the above screen shot I have 2 short headers ending in a fishmouth, not shown are the swiss cheese holes in the header

left engine.jpg

in the above screen shot you can see the augmenter/ejector? that encases most of the headers and incidentally sucks in cooling air from the front and directs it over the headers in an attempt to get the heat out of the cowling as quickly as possible. There will also be cool air directed over the portion of the headers between the engine and the augmenter. Visible in the first screen shot are some baffles in the augmenter that will hopefully reduce the noise even further.

I know the idea of a turbo has been thrown out for noise purposes but given the very experimental nature if this aircraft everything under the cowl has to be as simple as possible to reduce complexity and the chances of failure. Maybe if the plane makes it past the test phase I'll think about fancy stuff but not until then.
 

Billrsv4

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I'd like you guys opinion on my exhaust design for my aircraft. From what I've read the short runners may hurt me performance wise but I still think with a significant hp loss to the exhaust system I'll still have plenty of power for a small slippery single seater.

View attachment 55206
as you can see in the above screen shot I have 2 short headers ending in a fishmouth, not shown are the swiss cheese holes in the header

View attachment 55207

in the above screen shot you can see the augmenter/ejector? that encases most of the headers and incidentally sucks in cooling air from the front and directs it over the headers in an attempt to get the heat out of the cowling as quickly as possible. There will also be cool air directed over the portion of the headers between the engine and the augmenter. Visible in the first screen shot are some baffles in the augmenter that will hopefully reduce the noise even further.

I know the idea of a turbo has been thrown out for noise purposes but given the very experimental nature if this aircraft everything under the cowl has to be as simple as possible to reduce complexity and the chances of failure. Maybe if the plane makes it past the test phase I'll think about fancy stuff but not until then.
Will I can tell you that the design you have WILL NOT WORK. In a 13B the exhaust pulses would tear apart the fish mouthed pipes in less than an hour. The thing that cannot be overstated is how destructive the rotary exhaust is. First, heat. The typical exhaust gas temperature is 1600°F. Running a bit lean it can hit 1800°. The rotary is a ported engine. The 13B peripheral exhaust ports completely open in much less time than a valve can. There is also no valve in the way. The outflow is supersonic. Between the heat and the pulses rotary mufflers need to be all metal and STOUT. Heat resistant alloys are best. I have seen a brand name mild steel muffler die in a week. Checking the muffler for rattle should be part of your preflight. This problem is what brought down Mistral's demonstrator aircraft.
Bill
 

Vigilant1

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Will,. +1 to Bill's comment. Also, the noise will be horrendous. Not just loud, but dangerously loud to be around. You won't be welcome anywhere. As much as I've heard about the Wankel's exhaust and the challenges of quieting, I sometimes think a turbo might not be a crazy idea if space is at a premium and there's a desire not to have a muffler outside the cowl.
 

Billrsv4

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A rotary without a good exhaust could make you nauseous; the noise can make you sick. They are fun to play with but oh my gosh loud if a short or open exhaust. Another consideration is if you are willing to lose efficiency with a rotary, I bet it would be a race on running the engine vs pouring gas straight on the ground for an economy run. Pouring on the ground might be more efficient.
TFF,
As a FYI, not to be contrary, running a P-ported 13B engine with mechanical FI and electronic ignition, good long primaries before the muffler we see fuel flows at or less than a Lycoming of like output. Truly terrible mileage in the early rotary engines was in large part because they ran thermal reactors (afterburners if you will) to make smog with carburettors. Later FI and full engine management systems are much better. The cars still are only average at best, because the rotary thrives on high RPM. It makes a better aircraft engine than a car engine! The other thing to note is the higher output per cubic inch you make the better the rotary is. We are getting BSFCs between .4 and .5 in the 200 HP range. That number is comparable to just about any aircraft engine out there. Quite a bit better than dumping it on the ground!
Bill
 

Vigilant1

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Will,
Your design has the Spitfire and Corsair vibe going. You could also hang an aux fuel "drop tank" under the belly as a place to hide a muffler.
 
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