RotaryEvolution

iTrader: (30)

yes we all know the rotary engine is less efficient than piston counterparts. but reading some papers the VE levels aren't so radically different once the engine is in it's target peak range, still lower but not by a large margin.

but are the papers skewed? we know that a 9.0:1 CR rotary peaks at about 530whp on a standard 35R turbo. but put that turbo into a piston engine and you get a rather different tune of a peak range at about 750whp(even in ~2.0L engines)... that VE has a wider margin while pushing the limits of the air volume that the turbo can produce.

so, lower compression turbo rotaries must have a rather wider VE difference than the more current 13B-MSP which has more compression and side port exhaust vs peripheral early series.

with alcohol fuels more widely available i would tend to think that to increase VE of the motor to get more out of the turbos you effectively need to increase CR of the engine. of course the more compression in a rotary, the more risk, but alcohol is great at combating the additional ICT and EGT's and consequently knock suppression. but how stout of an ignition can you get to support this? we may as well need lightning to keep those plugs lit in these circumstances..

is the future really 9.4-10:1CR rotors, alcohol fuel and water injection? if you want to stay competetive then the VE of these engines needs to increase. this has been my aim, upping CR of the engines with turbos and running better suited fuel but if you look around, it is rather untreaded water still producing big numbers with high compression in a rotary. many 8 owners have failed attempting just this, but they also generally attempt it on old shitty gasoline, which has no place with a high compression force inducted rotary, superheating those side seals to crispy little chips.

a dangerous combination but come on, stock REWs are getting passed by OEM gasoline monster trucks off the showroom floor that getter gas mileage..

but does the port configuration play a big role in VE? the side port renesis is obviously the most up to date, while fully peripheral ported turbo motors are making the largest turbo rotary horsepower but also with quite overly massive turbos, low compression ratios and gobs of alcohol for fuel. obviously side port exhaust is out unless we begin hybridizing the motors from scrap 4 port MSPs, but i wonder if that might be feasable to make the most from the least.

alcohol and water for all! don't blame me for any hangovers..

C. Ludwig

iTrader: (27)

Think you're confused on the actual meaning of Volumetric Efficiency. When using the displacement of 1300cc for the 13B engine, these engines actually have outstanding VE. However, they are very poor in terms of Thermal Efficiency; which is to say, they convert a lower percentage of the BTU energy of their fuel into actual power than a modern pentroof piston engine would with the same amount of fuel. Sounds like that is what you're describing.

Higher compression may help, but their are much large fundamental flaws in the rotary engine that would need to be addressed to produce efficiency on the order of a modern piston engine.

peejay

Exactly what i was going to point out. Sure, bridge and peripheral port engines can get into the >100% VE range like most modern production cars (heck, production TPI Chevys and MPI 5.0 Fords were hitting ~104-105% VE in the mid 80s) but you'll never get around the horribly shaped combustion chambers or the sheer amount of surface area that the charge gets exposed to.

I liken it to flathead engines. There's a LOT of extraneous chamber surface area (although the flatties are still better than rotaries in this regard!) and due to the way everything is laid out, there's a point where higher compression results in reduced power because the air has to go through a smaller area.

At least with rotaries, that CR is in the modern-useable 9.0-9.7:1 range, while flatheads tend to be in the sub-7.0 range.

mono4lamar

iTrader: (32)

I agree, the power these engines make from such small displacement is great! Our only true flaw after we take into account our aftermarket parts curing the obvious is our combustion chamber. That's the only inherent flaw I see for the rotary...

RotaryEvolution

iTrader: (30)

well ok, my terminology was bad.. point aim is the efficiency to produce power from volume, the weak point. turbos react better to piston motors and make more power pushing the same amount of air and the way to lessen the gap between them.

piston engines still have the same tools to increase the gap again but i wanted ideas from people who may have more experience with high compression rotaries and turbos, the gains per CI of air. more or less when higher compression ratios are introduced?

as far as i see it the engine is bulky for it's displacement, weight for weight it needs more to compete. i'm seeing hondas with 35Rs pushing 500whp at 10 psi, barely even spooling the thing and at our peak for the same turbo..

the obvious benefit of higher CR is response, low compression turbo rotaries are such dogs that you may as well stamp them dyno queens(a strong argument for the low torque these motors have). high CR wakes these engines up to the point if you aren't careful with your foot you may wind up in a wall. but is the power gains still flat between the 2?

kind of embarassing when you do a dyno pull and feel accomplished pushing 500whp out of a turbo taking it to it's maximum potential and you see sheets of the same type turbo on a different engine of even less displacement(argumentative) pushing more from less. "that's all you got from a 3574R?"

anyways, the MSP is the most efficient so far at getting naturally aspirated horsepower, i wonder if it is worth testing more on forced induction with. yes, people have grenaded them left and right trying just that.

arghx

iTrader: (3)

I think the problem comes down to the fact that the rotaries we are using, even the Renesis, have a combustion chamber designed in the early 70s. A lot of energy is wasted due to inefficiencies that Mazda never spent the money to correct (through a clean-slate redesign), at least until their most recent push to modernize the engine.

It sounds like you are asking how we can narrow the gap with piston engines in terms of how much air we force into the engine and how much power ultimately comes out as a result. Better fuel and charge cooling will help, but you can do that with a piston engine too.

One thing to keep in mind is what you are comparing with. Hondas are considered to have very high flowing heads; V8s of course have a lot of displacement. Mitsu 4 cylinders seem to like a lot of boost. Subaru turbo EJ engines actual seem kind of close to a 13B in the sense that they need more turbo than competing engines to make a given power level.

j9fd3s

iTrader: (3)

on the terminology side there are a couple of things the SAE papers always mention, but we never talk about.

1. the rotary has more seal length than an equivalent (ha!) piston engine. so combine this with

2. the rotary has longer strokes. 270 degrees vs 180 degrees for a piston engine.

so there is/are more time AND more places for compression to leak. this is apparently why the rotary lacks low RPM power. this is also why chamber sealing is #1.

3. the rotary has 1 apex seal, a piston engine has 2 rings.

4. the SAE papers express the limits of a fuel, or engine by chamber pressure (IMEP or BMEP, http://en.wikipedia.org/wiki/Mean_effective_pressure). this really is a big subject, people who are qualified, write papers on just this. just to sum up though, pump gas seems to be able to handle a certain amount of pressure, water increases this. the engine mechanically has its limits too. its a big subject, do some light reading.

out of the SAE paper territory there seems to be some evidence that LOWER compression on a high hp turbo car makes more power, like PJ says there is more room. if you can cram double the amount of mixture into the chamber @TDC with a turbo, if you make the space larger, you also get more mixture. it must be a small effect, although its popular in japan. they mill the 8.5 rotors to 8.3.

the future is exciting! its direct injection, 3 plug, aluminum block, 300-350hp NA...

bumpstart

maybe mazda pushed off in a strange direction when they went the change for the more undersquare format with the 16 x ( longer , but narrower chamber )
myself thinks the long chamber was a disadvantage ( with current fuels ) in terms of the flame front direction / propogation
where it was shown to burn well in the direction of rotation but not towards the trailing end or towards the side edges of the rotor
- lots of quench area and a tendancy to stratify the rich regions of the mixture towards them tended to add to the HC problem and lower the overal efficiency
mazda used a trailing plug to combat this,, but you can see it helps none with chamber leakage or with burn towards the edges of the rotor

i would have thought that a better idea would have been to square the chamber more,, reducing the eccentricity of the crank and the "height " of the rotor, and perhaps increasing its width
- the difference here though -
is to square it enough to eliminate the need for the trailing plug to continue the burn to the far end of the rotor
- maybe even combine some CDI or laser technology to get in second leading yet effective non wasted strike
,, and have TWO side by side leading plugs per chamber ,, biased at the edges
,, to start flame FROM the very quench area that is the limiting factor in the equation
ie,, rotor width is no longer limited by the flame being quenched before it can work its way to mixture concentrating at the edges

decreasing the eccentricty has robbed our displacement and our TQ
but using side by side plugs allows us to minimise blow by duration ( in degrees )
and push rotor width back out to regain the lost displacement

the lesser eccentricity will also significantly increase the operational rpm of the engine ( in relative speed of the apex seals )
,, and so have boon in being the most effective method for the inherent poor chamber sealing---- rpms

and this makes the engine package longer,, but less tall,, and able to package lower in the driveline,, another rotary bane

John Huijben

iTrader: (1)

There's some info on that here:

http://www.rotaryeng.net/pat20090101103.pdf


Apparently having a larger stroke with less wide rotors improves combustion stability.
I think a side 'benefit' is that a larger stroke lowers the rpm range, making the engine more efficient at cruising rpm's.

Liborek

I'm pretty sure that PJ meant recess flow during combustion. I have pretty simple view on compression ratios, higher is better if the timing doesn't have to be retarded from MBT. I would guess they are doing this machining more for consistancy than lowering itself. IIRC power remain about the same from 9:1 - 12:1 CR, but emissions, BSFC and EGT's are doing quite crazy things Lower CR keeps peak temperatures and pressures also lower, which allows for more power when engine block is limited to certain peak conditions.

Look at the paper John posted. They examined many geometries and this one is simply superior in every regard as far as combustion goes.
Propagation to both breadth directions and rotational directions is faster, traling propagation will be always poor, no matter geometry or ignition or injection design. Strong turbulence and very small space between rotor face and housing literally quenches combustion.

There is heat release graph showing vast superiority of proposed geometry, if it will work same even at high load region, it will be major increase in efficiency.


In the regards of turbo limited power, we have to clearly identify two factors, if its compressor limited or turbine limited. Karack several times mentioned displacement. Actually, displacement can be very bad thing to have if we are examining certain turbocharger.
Small displacement piston engines can get away with very small hotsides and/or be very tolerant to increase in backpressure. This is the case of 4G63's, 920 whp from T3 frame, 6765 Precision billet is crazy. Honda engines are even more efficient, but their head flow is actually too good and they can't produce as much power from same turbo even with comparable displacement. They flow more air mass at lower pressure ratio on intake side, but they have to pass it through the same turbine. Consequently intake/exhaust pressure ratio is unfavorable which hurts both combustion efficiency and VE and overall pumping losses are greater.
Now take same turbo and use it on something with even bigger capacity - 13B. Pressure ratio across the engine is even worse.

If the above is in check, it goes down to brake specific fuel consumption at given air/fuel ratio. Many times I have seen how people throw around that boosted 13B has BSFC above 0.65 lb/Hp-hr, but without exact AFR, its meaningless parameter.

One member from another site posted figures of 0.681 lb/Hp-hr @ 10.2 AFR. and from one of the research papers, I have found figures of 0.54 lb/Hp-hr @ 12:1 AFR and 0.45 lb/Hp-hr @ 15:1 AFR.
Simple math converts these values to brake specific air consuption which can be inversely expressed as horsepower from certain air flow rate.

(BSFC*AFR)/60=BSAC
1/BSAC=X HP per 1lb/min.

Running this formula on numbers above reveals, that well builded and tuned rotary should be able to produce 8.6-9.2 HP@crank from each pound of airflow per minute. Note, this will happen at most efficient operating point I.e. at peak torque, peak power won't be as efficient. (another reason for producing power at reasonable engine speeds)

Simple fact is, that piston engines are getting even better. Biggest flaw of rotary isn't even large surface area/volume ratio. Althought is does hinder efficiency and increases cooling load, it doesn't have magnitude as some people may think.
Main problem is simply very slow and delayed burn of air/fuel mixture. Peak pressure is too late(consequently low) and does very little for making power. It can be clearly observed on EGT's, wankel engine has 50% more time for completion of burn(270/180°), but combustion is so slow that its still not completed when exhaust port opens.

Optimizing timing for extracting more energy from given cycle leads to higher peak pressures which leads to detonation, so it's vicious circle and compromises has to be made.

RotaryEvolution

iTrader: (30)

well there is already a nice spot on the rotor housings for direct injection that most don't use, ie the oil injector nozzles. not as advanced in the tract but it would take almost no effort to utilize that spot.

peejay

That's actually a horrible spot for DI.

The problem with DI and rotaries is that for low load, you'd want the injector almost where the trailing spark plug is, so you could pop in just a little tiny bit of fuel so that the majority of the fuel is near the spark plug when the plug fires.

Properly shaped combustion chambers is how DI engines can run at 50:1 or so. That's the "total" air/fuel ratio. In actuality, the charge is heavily stratified, since the injector pushes the fuel into a specifically shaped area of the piston.

Notice the problem? The chamber is always moving relative to the engine, so there'd be no single good place to put a DI injector, unless you did a staged DI system or DI/port injection scheme.

If you don't take advantage of the ability to get MASSIVELY stratified charge, you're missing out on the majority of the benefit of DI in the first place.

Anyway, something i just read on another forum, is more food for thought:

j9fd3s

iTrader: (3)

not in california they don't! we didn't even get the full VX civic, because despite using less fuel, it emits enough NOX that it doesn't pass emissions for California.

in europe they have some sort of emissions vs consumption sliding scale, but we don't in the US.

peejay

So they don't sell Ecoboost Fords in California?

Even the GM DI engines, which don't use the licensed combustion chamber technology, use highly stratified charge. They just don't work as well

j9fd3s

iTrader: (3)

it looks like we do, although i've never seen one, Ford might as well be Lamborghini here, its not common

max keiser

Lets face it.

The rotary engine is a failed concept end of story, it has a tiny segment to cater for freaks and odd ***** in society and the rest of humanity play with real engines that are efficient and make much more power per aspirated volume.

No internet theories and solutions will ever address the very well known short falls of rotary engines how many rotary powered cars did I see at TX2k12 taking on the twin turbo gallardo's or 1400rwhp supra's in street races? jack *****, why? cause they are crap compared to any half decent piston car.

max keiser

^ Do you even know what you are talking about newby?

The wankel has very poor Volumetric efficiency and it has very bad thermal efficiency, it does have excellent mechanical efficiency (the only good thing about it). The other two kill this engine in every application compared to any piston engine of the same vintage and equal power pulse to chamber displacement on an equivalent time scale.

Rotary engines struggle to attain 90% Ve on stock application, in racing versions it can go to 115% Ve but very good reciprocating engines are over 120% Ve or higher.

You need to compare an apple to an apple, not an apple to a *****.

Go watch a video of a Roton GP bike fitted with a NR588 (588cc chamber volume) Triumph engine, and see it only make 110bhp or so V's a 170+ bhp of a Honda of Mick Dohan of 500cc capacity (less than the rotary!) you will see the rotary with its larger chamber capacity getting lapped 5 times in the 1987 Assen Grad Prix. And that was a Peripheral Ported engine lol. The rotary really does suck for REVS and Volumetric efficiency and that is the most direct comparison you can ever get.

silverTRD

iTrader: (38)

you just called C. ludwig a newbie...LMAO!!!!!!!!!!!!!!good job max

rotory26

iTrader: (2)

So is there any consensus to the real VE of a N/A 13B useing the different porting options. Really would like these numbers for the fuel calculator. The VE number changes the required fuel by heaps.

Jobro

iTrader: (2)

The rotary is really only down about 7% in terms of BSFC at full load.
However at part load the rotary is down about 15%.

Racing around at wide open throttle with good tuning the rotary ***** all over the competition. We have EXCELLENT volumetric efficiency if we chose to.

We are easily 15% ahead of the piston engine in VE if we choose to design our cars that way.

To put that into perspective we are then comparing our 2616cc 13B to a 2.8L piston I6 turbo. However if the rotary has a higher RPM ceiling, we are soon out performing 3L engines.

Then you factor in what cars you can fit a 12A/13B into vs a 3L inline 6 piston turbo.

The chassi of many 800-1200kg cars can EASILY support a 13B, however it usually requires a 1500-1700kg car to SAFELY install a 3L inline 6.

Trots*88TII-AE*

iTrader: (11)

Here are a few diagrams from an SAE paper on rotary engines, "Recent Technology Development of High-Powered Rotary Engines at Mazda" from 1984.

Notice that the three types of port configurations compared are a sideport/streetport (S-A type), a J-port bridgeport - or combination port (S-C type) and Peripheral Port.



In figure 14 you can see that all three types of ports reach similar BMEP figures at different RPM's. Since BMEP is directly proportional to Torque given the same displacement, you can see that they make very similar torque at different RPM's, with the more overlap giving higher torque figures further in the RPM band (and effectively higher peak power figures). If you take thermal efficiency as being a constant in between the 3 engines, you can also conclude that they make similar VE peaks, again at different RPM's.

So back to your main question, how much VE can the rotary engine produce?



Up to and even over 120% volumetric efficiency. Also to note is that the Peripheral Port configuration compared in the last diagram (Fig. 14) used the "ideal" configuration of ~90-100* BTDC intake open timing.

C. Ludwig

iTrader: (27)

So, does this mean I can't accept the title of "newby"?

rurounixblade

iTrader: (1)

so that 120% VE can not be achieved unless you port the engine?

Trots*88TII-AE*

iTrader: (11)

Frigged if I know. I just like using big words out of them fancy research papers!

Alls I know is porting does not necessarily increase the VE of the engine, but it definitely changes where it happens in the RPM band. Just as an example, stock ports just might theoretically yield 120% VE at say, 4500 RPM, but most people wouldn't concern themselves much with that because power would drop off considerably past 8000 RPM and thus peak power would be less impressive vs a ported engine. That's why it's generally said that there is no "perfect" porting arrangement, it needs to be suited to the RPM band you're using as well as the turbo and/or manifolds being used.

On a side note, it seems to me more important to tune with regards to torque when messing with intake/exhaust porting and manifold tuning, just as Logan at Defined has taught me (among a million other things) since this is a better indication of VE. But as previously said, I think the OP was again referring more to
thermal/mechanical efficiency than VE.

P.S. Mr. Ludwig is teh l33t!