rotarygod

Mazda ran tests way back in the 70's that showed that power remained fairly constant between 9.0:1 and 11.0:1 falling off above and below this point. I have shown earlier in this thread that Mada has raised the compression ratio for emissions, not power reasons. Now as to why more compression doesn't seem to do anything on a rotary. Remember that on a piston engine, the air just gets compressed in one spot. It doesn't go anywhere.In a rotary, we are constantly moving air around the engine. We don't compress it in the same spot that we bring it into the engine or expell it from the engine. The rotor faces have a recessed dish area that determines the compression ratio. The smaller the dish, the higher the compression ratio. The problem with making it smaller is that air has a harder time getting from one side of the engine to the other through this dish as the rotor turns at it's smallest point. When we compress air in a rotary, we do more than just compact it into a smaller space. We also restrict it's flow as it is always moving. It is this restriction that puts pressure on the engine to the point that raising the compression ratio becomes counterproductive to overcoming internal airflow. As a result if we keep raising the compression ratio too much, we'll lose power, even on high octane fuels.

Renesis_8

Ah, its perfectly clear now, thanks again RG.

Just one more question... (for today) =D, I hope I am still making positive contribution to the thread, without turning it into my personal Q&A thread.

The question is on the side exhaust configuration in the Renesis. Just power wise, I understand its probably (and truthfully is) limiting power. Comparing the older NA rotary, do you think the side exhaust is any contribution to the power?

Its not the best comparison as the rotary engine + technology + materials advanced a lot in almost 20 years. But what I am thinking is really this.

I want to see it gone, however that'd again introduce overlapping. If the Renesis came with peripheral exhaust, and yes, it wont pass emissions, but we ignore that for now. Do you think the engine would still make the same power? a large decrease or possibly a little gain?

I am imaginating that DI would take care of the emissions, hopefully burn all the fuel in the combustion process. Then we can have peripheral exhaust for optimal flow. Add in a variable length peripheral intake. And only a small side intake for holding idle and low rpm, which can be open/closed.

I think the main problem lies in the huge overlap, and maybe side + peripheral intake is too costly/complex/impractical? and also emissions.. sigh.

I think I am going crazy
________
Web shows

rotarygod

All of the Renesis advancements are a result of the side exhaust configuration. Larger intake ports have some impact on power of course but not nearly as much as many people think it does. While some people will state that the peripheral exhaust ports can flow more than the side exhaust ports, this doesn't really tell us much. While airflow through a port is important, it's timing is also very important. The peripheral exhaust port has too much port timing. More is not always better. If we went back to a peripheral exhaust port in the Renesis we'd drastically lose power. The peripheral port can easily flow the engine's requirements. It can outflow them by a wide margin. The best system is one that flows only what you need it to at the timing that you need out of it. Expanding to what I said earlier, larger is not always better. Sometimes less is better! We have less total flow and less total timing yet we make much more power. That's a real world example if I've ever seen one.

rotarygod

I forgot who asked it or in what thread but someone wanted to know how fast the apex seals travel in relation to the housing surfaces. I found this chart that shows the speed relationship around the engine.

http://www.rotaryeng.net/APEX_SEAL_VELOCITY.JPG

Here's a chart on the inertial loads on the apex seals.

http://www.rotaryeng.net/APEX_SEAL_ACCELLERATION2.JPG

Apex seal temperature.

http://www.rotaryeng.net/APEX_SEAL_TEMP.JPG

Pilgrim

That was me, RG.

The first one (rotor speed) is confusing, at least to me. I see the rotor & housing, but can't translate the upper drawing. It appears to be a cutaway of a piston/cylinder at the same power point (max torque) as the rotary, and it looks like the speeds are compared one to the other.

If that's the case, the rotary actually stresses its sliding surfaces more than a piston engine. That surprises me; I'd have thought otherwise.

The rotary clearly has the advantage in inertial loads - it doesn't have that 180 degree change in loads that is so hard on bearings and other parts.

Thanks for the info.

Have you ever come across a chart that shows best fuel economy RPMS at a load? You'd need a vacuum gauge to apply the info accurately to the vehicle's operation, but even knowing the RPM level might help some. I am suddenly attuned to fuel economy since I made a 320 mile round trip to Seattle yesterday and got 10.8MPG cruising at 75MPH in sixth gear. My Dodge Ram Hemi beats that by 5MPG for the same trip at the same speed.

Pilgrim

rotarygod

That's not a picture of a piston. That's a view looking at the rotor from the rotor faces. You are seeing side seal stresses.

Pilgrim

Well, I didn't really like the piston interpretation, but it was all I could figure out.

At first glance I thought it was what you said, but now I still don't understand how the velocity figures relate to the drawings, though.

Thanks.

Pilgrim

jird20

Dear RG,

I am trying to recall one of your instructive posts that I read long ago. In that post, you were saying (I might not recall correctly) that a rotary engine needs more air flow than a piston engine to get the same power. This does not make much sense to me but there is probably an explanation for it.

I think this thread is the right place to review that topic.

Could you explain how air flow relates in a rotary vs a piston engine?

Thank you very much.

btw is there any possibility that you send me an electronic copy of the SAE papers related to rotary engines? I am very interested in learning about this field since I work in a company that designs and manufactures Diesel and Otto engines for marine and stationay applications (name is GUASCOR). Thank you very much again.

Cheers

jird20

dsmdriver

iTrader: (3)

The basic issue with a Rotary engine is that due to the shape of the combustion chamber, the fuel is not used as efficently as it is in a round combustion chamber. It is less thermodynamically efficent than a piston engine, so it needs more air and more fuel to produce the same energy output.

MazdaManiac

iTrader: (3)

^^ That is it in a nutshell.
The BSFC for a rotary is about 15% higher than a comparable reciprocating piston motor.

maikelnait

Well, MazdaManiac, and Rg as well, you are really well respected sources of rotary culture in Spain, as my good friend Jird20 is , please feel free to explain further.

Thanks a lot,

Maikelnait

Renesis_8

Bump! dont let the good threads die.
________
Hyde Park Residence

Renesis_8

One of the reason the rotors are cast iron is because it expands slower than the aluminum housing. Major drawback is the weight.

Browsing thru wikipedia.

Thermal expansion for Iron : 11.8 ?m?m?1?K?1
Thermal expansion for Titanium: 8.6 ?m?m?1?K?1
Thermal expansion for Aluminum: 23.1 ?m?m?1?K?1

The units mean they expand how many micrometer in a meter of metal with every degree of temperature increase in Kelvin.

I am just suggesting Titanium because I know it is lightweight metal off my head, however it is not as strong as iron. The melting point is almost the same as aluminum too.

Casting the rotors out of titanium could greatly reduce the weight of the rotors, the cast iron rotors in the renesis weights 9.2lbs each according to Racing Beat. Using the density of Fe and Ti, I think it would be around 4.5lbs for a Ti rotor.

Although the price would dramatically increase, I believe it would still work in race applications. Could possibly reduce the weight by 30-40% of the engine if they use better metals/alloys for the housing, plates, and rotors.

Advantage would be a higher redline, less load on parts, seals, etc.., more reliable.

I am also interested in the harmonics in the engine, I do not have any knowledge in regards to that, I'll admit I learned everything from this forum thru years of reading(join date is last yr, but I been reading since 2003) The rotary engine self-destructs at/near 13k RPM, is there anyway to get around the harmonics so that the max rpm can be raised?

edit: actually Ti is alot harder than Fe.
________
Side effects of avandia

Gomez

That is freaking ridiculous fuel economy. There is something seriously wrong with that car.

Pilgrim

Yes, you're right. It runs fine, but the mileage sucks - or did. See, things have changed.

What I posted was after two trips to Seattle on Interstates 84 and 90, about 320 miles round-trip, and there is a lot of up, then down on it. The cruise control was set at 75. And the mileage I cited above was pretty damned well-measured and accurate. The runs were made with between 400 and a thousand miles on the car.

Since I posted that I have made two more trips on the same route, cruise control at 80. Mileage has been 18.1 and 18.5.

On a third trip, which built the mileage from 1,100 to 1,500 miles, I took the Interstate over on the previous route, but returned via another one, a two-lane, twisty highway over the mountains (Stephens Pass, for you folks in Washington). No cruise control set on the return, and the return trip was done at an average speed of 65mph, calculating distance into time.
And the gas mileage was 19.3, despite a lot of accelerator use.

What brought about the improvement? I'm not sure, maybe it was sunspot activity. Or a gravity warp. Or ten thousand invisible butterflies pushing me.

I wonder, really, if the computer has some sort of enrichening built into the injection system that operates for the first thousand miles or so. Or something.

All I know is I'm satisfied now.

Pilgrim

zoom44

what gear were you in for the 10 mpg trip? do you have the gallons filled vs miles at fill up still?

ive gone two ways from portland to wenatchee- up 5 to 90 and then 97 to 2 over to wenatchee and also out east on 84 then north on 97 to 2.

going up and back both ways between 70mph and 80mph(with a ticket just outside of wenatchee at 80-oops) ive had between 21- and 24 mpg for all the legs.

Pilgrim

Sixth as long as possible, but I don't let the engine lug. If I can't get decent throttle response with the gear I'm in I drop one or two. I use the cruise cont but I still pay attention to how happy the engines feel.

There are a couple relatively short spots on I-84 and 90 where it calls for fifth, and Blewett pass has a couple short stretches where I use fourth.

I don't keep a fillup log, but I may start if the mileage goes erratic on me. Anything over 16 and I can smile. Eighteen and up and I'm effing ecstatic.

I'm going to call it coincidence, but the improvement took place about the time I began premixing.

Pilgrim

Nubo

Ti melting point is vastly higher than Aluminum. That's why they make things like jet turbine blades from Ti alloys.

AFAIK, Ti is a b**** to machine; and there's a lot of machining to a rotor. The price would be incredible. Another problem with Ti is galling. Not sure how that would play out with the apex seals that move in their slots. Certainly you'd need some other metal for the bearing; maybe inserts for the apex slots too. There we go with dissimilar metal expansion again, and perhaps galvanic corrosion. Maybe these problems could be solved but I'm wondering if a set of Ti rotors would cost more than the car?

rotarygod

Don't use bearings! Just create a new rotor and build the bearing in. I know some people say that if a bearing goes out, all you have to do is replace it and put the engine back together. Bearings should never touch each other. That means no oil present. For the most part a bearing failure is uncommon so it's not much of a concern.

olddragger

iTrader: (3)

does the leading edges on the rotor's need to be blueprinted? Are there any advantages to coating the combustion face on the rotor?
Oldragger

shaunv74

That's not quite correct. They make Turbine compressor blades from Titanium not the turbine blades because like magnesium titanium is combustable. It's good for about 800F. Anything above that and it goes plastic so it would have to be cooled. Also I wouldn't expose it to the combustion chamber. That's how titanium fires get started and if that happens your car burns to the ground from the inside out.

shaunv74

What about ceramic rotors? they could run at very high temperatures. You'd need to have some kind of metallic fiber reinforcement so they don't crack from shock loads. Or ceramic coating the rotor faces to reduce the rotor metal temps. That may open you up to aluminum or other lighter metals/plastics.

nycgps

iTrader: (1)

I think everything comes down to cost concerns.

Renesis_8

I dont know how the rotors are made, are they machined? or casted from a mold. I know NSX uses titanium connecting rods, so there has been Ti parts used in ICEs. But it seems it might not be a good choice in this application in a rotary engine. Perhaps other alloys. Or just simply aluminum alloys like all other pistons engines. That'd lower the weight down by a lot already.

It seems using light weight materals for the rotors hasnt really been discussed before, there are plenty for the plates between housings. I was just reading the thread about going to 13krpm that guy started.

Biggest concern is E-shaft flex, well I thought maybe we decrease the load on the shaft then we can go higher without making an even stronger shaft. Why go that high?, certainly not in street application, just racing. 9000rpm is enough for a road car.
________
Volcano Vaporizers

Renesis_8

I am sure some aluminum alloys can stand up to the combustion temperatures of the rotary engine. Maybe its too much chemistry and metallugy here. But the same alloy is used in almost all piston engines now. So I am sure there is a way to make it work.

As for the expansion rates, I think with different use of aluminum alloys would solve it. rotors expand slower, and housing faster.

Did they cermaic coat the 787B? They certainly did for the housing, not too sure about rotors.
________
California Medical Marijuana Dispensaries