You need to do more research..... A LOT more.

-J

 

I'm not even going to bother to try to explain it...

 

Wow! I'll try to correct some of this as simply and quickly as possible as I don't have time to write a book. I'm not even going to touch the air pump comment so I'll skip it.

If you could seal off both halves at top dead center by completely filling in the tub, you couldn't turn the engine!!! Air can't pass through! If you ignite this air, what's it going to do? The air has nowhere to go. If you ignite the trailing plug with air only on that side of the motor, it'll try to spin backwards. This can't happen anyways as without any dishes in the rotor faces you really can't spin the motor far enough to ever get any air over there. My comment on dish size was exactly to emphasize that air has to FLOW through a rotary and not only get compressed in one location which happens to be the same place that it's brought in and expelled from. They don't work like that. Too small of a dish and you get high losses no dish is practically no rotation assuming you can completely seal it off.

Compression on a diesel is fundamentally no different from that on a gasoline engine. It can only be so high until you lose control of the flame front travel during ignition. It has nothing to do with blowing the heads off. If that happened all they'd do is to design a stronger head and use better head bolts and gaskets! Compression pressures are not even close to as high as combustion pressures. The one thing I don't want to hear is that diesels run on detonation. They don't!

 

i dont mean to burst your bubble but i will. for all you nay sayers. yours...

reference link #1 AND #3 down at bottom of page;



I dont believe it mere coincidence that wankel was working on a rotary supercharger before developing his wankel engine.



and if thats not enough proof check out reference link #3(THE original wankel patent) then scroll down to "US Patent References:" the two links reference PUMPS! of the fluid type, not just combustion engines! who would have thought that wankel's rotary piston engine was BORN of simple compressers (AKA air pumps)?!



reference link #2
apparently Curtiss-Wright believed such an insane method would work to increase effective pressures high enough to ignite diesel that they went through the trouble to patent such a design. they wouldnt waste their time and money for nothing. at the very least it was plausible.



^this i admit to being wrong about. my bad.

other than that. i rest my case. have a nice day



references for issues of credibility:
1st:
http://foxed.ca/rx7manual/manuals/RE...amoto-1981.pdf
yamamoto (head of wankel engine r&d at mazda in the 60's) published book

2nd:
http://www.freepatentsonline.com/3994266.html
Curtiss-Wright patent of diesel wankel by spliting leading and trailing chambers

3rd:
http://www.freepatentsonline.com/2988065.html
Felix Wankel's ORIGINAL patent

 

And this proves what? I told you I wasn't going to touch the air pump comment and I didn't. I didn't say there were never any rotary air pumps. There definitely were. Jet engines were inspired by turbochargers too!

Curtiss Wright still had a dish in their rotor. They had to. You either need a high compression ratio to get compression ignition or you need a low compression ratio and a blower. The key is with the effective compression ratio rather than they dynamic compression ratio. Yes there's a difference. The static is what you know the engine to be at, 9.0:1, 9.4:1, 9.7:1, etc. The dynamic is what it actually is at the point of ignition. This changes based on VE (volumetric efficiency). If you don't have a high static compression ratio, you can use boost to raise the dynamic. That's all boost does.

There are a few things to keep in mind about Curtiss Wright. First off they either used spark or glow plug ignition in their diesel rotary attempts. They never had true compression ignition. Last, they never produced it!

I'm not sure what you are trying to disprove of my statement but you didn't do it.

 

I am not sure what needs to be explained...

 

It was Rolls Royce who made the first diesel rotary engine with a 2nd rotary engine to raise the compression enough for the first. The Curtiss Wright rotary engine was just a run on anything engine, as rotarygod says. The military likes to be able to use whatever fuel they capture.

 

first of all i have to apologize for allowing myself to become immature. i dont respond well when i feel patronized.
anyways back to the discussion, one of the major reasons for the dish is not only to allow proper flow but (in which i believe is the larger determining factor) it is there to help decrease surface to volume ratio. that alone is a major design problem of the wankel. too much surface relative to volume hence increased heat energy loss through the coolant. which is supported by the fact that rotarys run hot. its all in yamamoto's books. the dish design can also been seen in the top of diesel pistons to help decrease the high surface to volume ratio unfortunately associated with engines of high compression ratios.
also it should be noted that the shape that maximizes surface to volume ratio is a perfect sphere. the shape at tdc for the rotary is a weird banana shape at best. of which i dont believe you could ask for a worse 3d shape.

 

I wasn't patronizing you. Sorry if you took it that way.

A dish in the top of a piston isn't the same thing as a piston compresses air in place. It doesn't have to flow air to another part of the combustion chamber. It enters, gets compressed, ignited, and exhausted all in the same place. This doesn't happen in a rotary.

There is a ton of surface area in the rotary due to air and fuel having to move across the engine and this is what lowers the efficiency. Fuel sticks to the walls, heat energy is lost, etc.

When you get above 11.0:1 compression in a rotary, power goes down. You have too much loss to lack of airflow through the dish. There is a chart that shows this in Yamamoto's book.

 

Speaking of compression, does anyone believe these claims...

MOLLER INTERNATIONAL ACHIEVES BREAKTHROUGH IN ROTARY ENGINE PERFORMANCE
Davis, CA, May 14, 2008 – Moller International (OTC-BB: MLER) announced today that it has
achieved a major breakthrough in rotary engine performance. A version of the Company’s
Rotapower® engine is designed in such a way that the engine’s two rotors operate in series rather
than parallel. This design allows the first compressor/expansion rotor to supercharge the second
power rotor while the exhaust from the power rotor is further expanded in the
compressor/expansion rotor, extracting additional power. In effect, the engine operates in what is
termed a compound cycle. Because of the additional energy captured from the exhaust gases,
engine noise is reduced by 93% and exhaust temperature is reduced by 47%. Moller
International’s non-compounded Rotapower® rotary engine has already demonstrated a fuel
consumption 12% below that of the new Mazda Renesis rotary engine. Compounding is expected
reduce the Rotapower® engine’s fuel consumption by an additional 25%.
Rotary engines are particularly small and light relative to their power output and nearly vibrationfree
in operation. Compounding makes the Rotapower® engine potentially much better than the
piston engine in fuel consumption as well. This was the major limitation that prevented the rotary
engine from supplanting all piston engines. It now becomes an attractive candidate for the Plugin
Hybrid Electric Vehicle (PHEV) market where weight, space, fuel consumption, emissions and
vibration are all critical. The Rotapower® engine previously demonstrated its ability to meet
California’s Super Ultra Low Emissions Vehicle (SULEV) standard without exhaust aftertreatment.
Moller International is in the final phase of negotiations to license worldwide production and
marketing rights for its Rotapower® engines to Rotapower Engine Systems, Limited of
Southampton, United Kingdom.

from http://www.freedom-motors.com/

If true then I would think all the auto manufacturers would be very interested and a good performance diesel rotary may be next. I have to say I'm skeptical and still don't get how they could achieve what they claim.

 

Rolls Royce did exactly what Moller Int. claims is new in 1971 for its heavy fuel Wankel for its UK Ministry of Defense contract, so it should be possible for Moller as well- LOL.

 

Yea, but Moller is able to reduce noise by 93%, exhaust temps by 47%, and fuel consumption by 37% over a Renesis ;-) The Renesis wouldn't be so bad on fuel if it wasn't geared so low to get performance. I bet the 16x in a RX-8 will be able to go back to higher gearing with the additional torque. Maybe back to 4.30's in the rear and wider spaced tranny gears with about 280 HP & 180 lb/ft of torque N/A? Maybe 19 city 27 highway? Just guessing/dreaming of course.

 

yea like blue said, its already been done. it adds too much weight. better off going turbo charge to build effective compression as that system acts exactly like a turbocharger(eg. uses waste exhaust gasses to supercharge intake.) except heavier. but maybe this time around, who knows.\


also @ rotarygod
one thing that should be realized is that a restrictive flow through the rotary is not all bad. for example, once the compression stroke of the rotor approaches tdc it becomes more restrictive at the "peak". understand though that as the air is being held or squeezed back that it in effect builds upon the effective compression so that 11:1 compression in a rotary at 100% volumetric efficiency is comparable to say 12:1 compression in a piston motor at 100% volumetric efficiency. yea it makes sense that you could say a lower dish lends to negative force in the opposite direction in the rotary but isnt building effective compression in any motor a negative force? you could place that same argument upon diesel motors, they build relatively high compression before ignition therefore a relatively higher negative force in the opposite direction, but yet they still are more fuel efficient than lower compression gasoline piston motors because the added benefit of the higher compression burn out weighs the increased negative force up until a certain point that it just becomes truly negative work.

 

It's pretty easy to see how it's quieter and has cooler exhaust temps. The combusting rotor fired it's exhaust into the other rotor housing which really acts as a big muffler. Heat is obviously absorbed here as well and I'm sure coolant temps will be higher as a result since less heat is going out the exhaust. It's got to go somewhere.

This configuration is basically what is referred to as turbo compounding. Imagine a turbocharger that has it's main shaft connected to the crank. That sounds like a supercharger and it is except that some of the exhaust energy is being captured and sent back to the crank. This increases fuel efficiency.

What is Moller claiming for horsepower? It's easy to claim less emissions and fuel usage if your power is lower. Is their power level comparable to a Renesis? If so then the next question is how big is their engine package? If it's comparable, and I don't see how it could be, then they could be on to something. As was pointed out though it's not their original idea.

 

Yes compression is a negative force. However a rotary compounds the issue by having to also flow air and overcome it's losses. We aren't only compressing air. We are moving it too. After airspeed through a system passes about .6 mach, it really gets hard to move and pumping losses go up at an alarming rate. Heat buildup is also much faster. This all happens through the rotor dish.

I know someone will point out that boosted engines have a ton of air going through this small area. Fortunately it is being compressed first by something other than the rotor, namely a turbo or supercharger. This extra air also has extra oxygen which can be used with the extra fuel to provide a greater bang to overcome and losses here. Air actually momentarily flows backwards through the rotor dish right before combustion!

 

i see your point rotarygod. thanks for the insight.
but then what if the trochoid shape was redesigned so that there is no longer a "peak" or such a restriction? is it then possible to further increase compression without killing the motor?
i ask because me and a good friend want to create a prototype diesel rotary engine without such a restriction on compression ratio limits and without killing the motor. in others words a rotary with a higher k constant as defined in the yamamoto books. then hopefully sell such an engine to the aviation community as an air-cooled experimental motor that offers reliability, great power to weight, fuel efficiency and simplicity at a competitive rate. do you believe such a design is realistically plausible to meet our goal?

 

At one time diesel engines had low compression. This was before they were direct injected but were injected in the intake manifolds or through a type of carb. Diesel fuel has a very low octane rating, somewhere between 20 and 40 although you never see it listed anywhere. It's only through careful metering and flame front control due to it burning slower that allows us to use such high compression ratios today. Static compression ratios on diesels used to be as low as 8:1. Obviously it won't compression ignite. To overcome this they had to raise the dynamic compression ratio and they typically did it with roots superchargers. The dynamic comression ratio is what makes power, not static compression. These engines did have to use glow plugs to start. Some still do but others don't.

 

but we'd like to achieve it without any assistance from a spark plug and only through a diesel injector because the more holes that have to be placed in the rotor housings for fitting spark plugs and the like, the more gas exchange will occur between the chambers hence loss of efficiency.

 

It has been done as a company is building a small 1 rotor 15 hp apu for business jets that is straight diesel with direct injection. It uses a glow plug. I'm at work but have the picture saved on my home computer. I need to find it.

 

i believe what you are referring to is the yanmar diesel rotary. im looking at the only patent by yanmar for diesel rotary and it seems as if its also of the rolls royce type unfortunately.

 

Found it. It's the Pats APU. Here you go. Scroll down.

http://cp_www.tripod.com/rotary/pg08.htm

 

I just checked with a friend of mine in the know... Apparently the PATS engine was originally developed by a govt. contractor here in MD.. it never worked well enough to replace the avgas powered unit. Some of the developers bought the rights and started PATS. They have been trying to make it work for a long time with marginal success.

 

I have no doubt that the failure (or lack of performance required) was solely due to the compression/rotor dish issue. If it was only about compression and not about internal flow as well, it shouldn't have been a problem.

 

Well, I'm sure that compression wasn't the only issue. I know that a heavy fuel equivalent of this engine has been on the list of desirables for a while now and that many govt $$ have been thrown at the problem. I'm sure bumping compression would have been the first thing tried. Whether or not you can say the only other hurdle would have been internal flow as a reult of the compression bump, I'm not so sure.

I only mentioned it because I didn't want anyone to think that just because there was a product in the marketplace, that it was very successful product. The engine that it was molested from makes 35-40 hp NA on gas. 18hp on deisel says that its very inefficient. The only reason it is desirable in their application is because it runs the same fuel as the plane, is small and cheaper than a turbine.

 

I don't get this need to have to have compression ignition when working with heavy fuel. I personally was involved in a project here at work (NASA) that took a single piston 2 stroke gas/oil drone/UAV aircraft engine and converted it to run on heavy fuel (multifuel I suppose, it would run on JP8 and gas). The aluminum head was milled off the cylinder jug and a machined steel one was bolted on. The new head had a plasma chamber built into it. Basically there was 2 small recesses in the vicinity on the spark plug (yes, even on diesel it still was spark ignition). Our results were nice though. We didn’t even have to rejet, it ran fine on gas and because the forgiving nature of diesel type fuels due to air fuel ratios, the engine ran great on JP8 without a carb mod. We dyno'ed both before and after the head mod and both on the modded head with gas and with JP8. The findings were increased in power with the new head on gas (most likely due to slight bump in CR) and same power on JP8 as the engine left unmodded. So if heavy fuel is wanted to be run, I don't see why they couldn’t simply use spark ignition with no loss in power compared to gas. I understand that compression ignition in theory is more efficient, but obviously it doesn't work well (so far) in a rotary. My point is, why don't they just use spark ignition on the heavy fuel engine, it can run off of gas and the same fuel as the jet its installed on with minimal power loss if any? I know there is a company that manufactures heavy fuel rotary engines for the aviation market (did this freedom comapny buy out the rotary company I'm thinking of?).

~Mike..........