16x Delay
03-06-2010, 10:52 PM
#301
Aluminum is not new to Rotary Engines.
There are Aluminum side housing for years. conducts/release heat better than stock cast iron housing and show very little wear. but cost couples times more so its not good for production engines.
Not to mention, Mazda even tried Aluminum Rotors. but again, it ran really good, it last longer than cast iron and might lighter, but the production cost alone will kill this car.
There are Aluminum side housing for years. conducts/release heat better than stock cast iron housing and show very little wear. but cost couples times more so its not good for production engines.
Not to mention, Mazda even tried Aluminum Rotors. but again, it ran really good, it last longer than cast iron and might lighter, but the production cost alone will kill this car.
03-07-2010, 02:09 AM
#302
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Aluminum is not new to Rotary Engines.
There are Aluminum side housing for years. conducts/release heat better than stock cast iron housing and show very little wear. but cost couples times more so its not good for production engines.
Not to mention, Mazda even tried Aluminum Rotors. but again, it ran really good, it last longer than cast iron and might lighter, but the production cost alone will kill this car.
There are Aluminum side housing for years. conducts/release heat better than stock cast iron housing and show very little wear. but cost couples times more so its not good for production engines.
Not to mention, Mazda even tried Aluminum Rotors. but again, it ran really good, it last longer than cast iron and might lighter, but the production cost alone will kill this car.
I'm sure it's a matter of how the rotor material transfers and reflects heat more than anything else. On the housing side of things, it makes sense to go all aluminum. Heat more readily leaves through the housing where the ignition and exhaust phases take place meaning the housing becomes less warped by the expansion of the material. Those parts are already too warm compared to the rest of the engine due to the set positions each phase of the otto cycle happens in. On the flip side though, a cool rotor from an "avoiding expansion under heat" standpoint makes sense. Sealing is less of an issue and tolerances can be tighter. Less oil burn, better compression, all good things. But a rotor that just sucks heat out of combustion is wasting energy (so is the housing but what are you gonna do when millions of explosions happen all in the same place without time for cooling?). Basically a rotor should be made much more like any old cylinder wall: light weight, reflective of heat, relatively cool and relatively constant in dimensions. Aluminum doesn't satisfy the 2nd requirement terribly well and that has a huge effect on everything from torque to mpg.
@Reddozen:
That's all I can say right now? If you know something I won't ask you to reveal it but I am curious: is my line of thinking correct? I assume if you know what materials are better, you know why they are better as well.
03-07-2010, 08:18 AM
#303
Same airflow, same fuel flow, more power, lower BSFC, WIN
In terms of coatings, NASA did huge study about adiabatic wankel engine, all kinds of coatings applied on all surfaces, cooling load usually decreased by 5%, EGTs increased by few percent, overall thermal efficiency, maybe 2% increase...
03-07-2010, 07:42 PM
#304
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Did these people circulate any numbers? I realize it's unlikely a few groups outside of Mazda doing such a thing would result in a paper. Still any data is enlightening but as of now, all I've heard is "Some people did this" said in one form or another. No one seems to be able to name names or direct me to any literature which is a bit telling.
03-08-2010, 04:26 AM
#305
One Shot One Kill
Many RX-7 owners don't like the RX-8 for having 4 doors and for weighing a lot more than the 7. Many also don't like the Renesis out of ignorance. They just don't look at the RX-8 as a pure sports car. Nevermind the fact that the RX-8 is faster than all RX-7s but the 3rd gen and can out handle ALL of them! I drive a 20 year old car that uses technology from a quarter of a century ago, is no faster in a straight line than the average compact car today, and has fuel economy worse than some SUV's. I just like it for what it is and could care less what car is faster or better. Many others don't feel that way though. They need to be thought of as being better than everyone else.
03-08-2010, 07:36 AM
#306
Aluminum can work for a rotor, but your problem is that you still have to burn high octane fuels to keep the burn temps down, otherwise they'll melt.
The melting point of 6061 aircraft grade aluminum is 1090F.
In all honesty, you need a material that can handle closer to 2000F to be thermally efficient. You don't want a material that soaks up heat. You want a material that reflects it, otherwise you're loosing horse power in heat loss, and aluminum soaks up 4 times more heat than cast iron... no thanks.
Take cook ware for example.
http://www.dutchovendude.com/dutch-o...aluminum.shtml
Heating:
Cast Iron: Heats slowly and evenly. Retains heat.
Aluminum: Since it has less mass, it heats faster, but may have hot spots and loses heat faster.
Melting:
Cast Iron: Melts at 2000 degrees. Won't melt on a fire.
Aluminum: Melts at 1200 degrees. Chance of melting on a very hot fire
Hot spots, and unpredictable heat spread across the rotor face!? Higher chance of detonation is not my idea of a good material to use, and the melting point is close to the engine's exhaust temps in the header...
I'm just saying I wouldn't personally spend all that money on a risky material when I know it's limitations / downfalls.
03-08-2010, 10:16 AM
#308
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The hottest the rotors ever really get up to in any one point, and it's not uniform, is about 500*F or so. The oil carries heat away. Aluminum isn't going to melt. Not even uncoated. Coating it would be better though. They have been made before btw. It's not a new concept. Mazda uses cast iron for only 1 reason and it isn't a very complicated one. It's cheaper. That's it. Don't overanalyze it. It's not an engineering decision. It's an accounting one.
Don't form an opinion based off of the use of any materials in the 16X. It is really a concept engine. I guarantee they have cast iron versions being tested. In 1988 Mazda stuffed a 20B in an FC and everyone thought they'd get one. Didn't happen. In 1989 Mazda showed off an all aluminum housing 20B that had ceramic seals and coatings and people thought we'd get it. Didn't happen.
I don't think we should get a larger engine. I think we should get a smaller one but with a turbo. I think we should keep the same rotor height but decrease the width to get the same width to height ratios as the 16X which is where the efficiency gain is. They didn't gain efficiency by making the rotors taller. It was the ratio that mattered. Make a smaller engine that makes the same power and stuff it in a lighter car. That's what we need. 25 mpg city and 35 hwy would be attainable all day long.
Don't form an opinion based off of the use of any materials in the 16X. It is really a concept engine. I guarantee they have cast iron versions being tested. In 1988 Mazda stuffed a 20B in an FC and everyone thought they'd get one. Didn't happen. In 1989 Mazda showed off an all aluminum housing 20B that had ceramic seals and coatings and people thought we'd get it. Didn't happen.
I don't think we should get a larger engine. I think we should get a smaller one but with a turbo. I think we should keep the same rotor height but decrease the width to get the same width to height ratios as the 16X which is where the efficiency gain is. They didn't gain efficiency by making the rotors taller. It was the ratio that mattered. Make a smaller engine that makes the same power and stuff it in a lighter car. That's what we need. 25 mpg city and 35 hwy would be attainable all day long.
Octane tells you nothing about the temperature of the flame front or heat released when the fuel is burned.
03-08-2010, 10:36 AM
#310
Did these people circulate any numbers? I realize it's unlikely a few groups outside of Mazda doing such a thing would result in a paper. Still any data is enlightening but as of now, all I've heard is "Some people did this" said in one form or another. No one seems to be able to name names or direct me to any literature which is a bit telling.
and test it.These guys mentioned that in 800 rwhp 13B turbo they picked up average 60 rwhp across the board in boost, in off-boost zone(less than 5,000 rpms) they picked up average 15 rwhp with no increase in water/oil temp...
03-08-2010, 10:41 AM
#311
Administrator
no but they gained STROKE and thus higher torque. which along with the increase in volume provides for higher power while the DI and other geometry changes make it more fuel efficient than the current renny. and not just a percentage equal to its increase in power so that in the end we still have a 16/22 car but actually better so it gets closer to the numbers you would like to see.
03-08-2010, 05:14 PM
#313
One Shot One Kill
the turboed small engine will have increased torque, but less efficient than just simply increasing the stroke of the rotor. As you said way back, the design of the rotary force it to have less torque than an equivalent displacement piston engine.
larger rotor = more stroke = more torque = faster to get to speed and lock in on the cruise setting
smaller width = less thermal loss = more efficient
where a turbo will produce torque, but also increased heat of the engine.
increase of the heat increase rate of heat loss, lower efficiency.
sizing down the rotor will also decrease the stroke, lower the designed efficiency of the engine's torque.
Where i can see a turbo come into play is to replace multiple ports, on high rpm, have a turbo kick in to deliver the necessary amount of air so the engine don't starve for air.
just my 2 cents.
for what it's worth, one time i had a full car and was going on a slight hill (country highway). on 6th gear i was slowing down because i couldn't provide enough torque even WOT and had to downshift to 5th gear.. we really need some torque.
larger rotor = more stroke = more torque = faster to get to speed and lock in on the cruise setting
smaller width = less thermal loss = more efficient
where a turbo will produce torque, but also increased heat of the engine.
increase of the heat increase rate of heat loss, lower efficiency.
sizing down the rotor will also decrease the stroke, lower the designed efficiency of the engine's torque.
Where i can see a turbo come into play is to replace multiple ports, on high rpm, have a turbo kick in to deliver the necessary amount of air so the engine don't starve for air.
just my 2 cents.
for what it's worth, one time i had a full car and was going on a slight hill (country highway). on 6th gear i was slowing down because i couldn't provide enough torque even WOT and had to downshift to 5th gear.. we really need some torque.
03-08-2010, 08:27 PM
#315
Intended acceleration
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One reason for using a cast iron rotor over aluminium is the much lower thermal expansion coefficient (less than half), which means the rotor is less likely to sieze if it overheats.
03-09-2010, 10:50 AM
#316
In piston engine, piston crown is under far higher thermal stress than rotor face, yet no issues...
Mechanical load(rotor weight) on rotor bearings/e-shaft journals is huge and it increases with the square of the speed, rotor face can physically hit trochoid surface, due to deflection of e-shaft...
03-09-2010, 10:53 AM
#317
Registered
the turboed small engine will have increased torque, but less efficient than just simply increasing the stroke of the rotor. As you said way back, the design of the rotary force it to have less torque than an equivalent displacement piston engine.
larger rotor = more stroke = more torque = faster to get to speed and lock in on the cruise setting
smaller width = less thermal loss = more efficient
where a turbo will produce torque, but also increased heat of the engine.
increase of the heat increase rate of heat loss, lower efficiency.
sizing down the rotor will also decrease the stroke, lower the designed efficiency of the engine's torque.
Where i can see a turbo come into play is to replace multiple ports, on high rpm, have a turbo kick in to deliver the necessary amount of air so the engine don't starve for air.
just my 2 cents.
for what it's worth, one time i had a full car and was going on a slight hill (country highway). on 6th gear i was slowing down because i couldn't provide enough torque even WOT and had to downshift to 5th gear.. we really need some torque.
larger rotor = more stroke = more torque = faster to get to speed and lock in on the cruise setting
smaller width = less thermal loss = more efficient
where a turbo will produce torque, but also increased heat of the engine.
increase of the heat increase rate of heat loss, lower efficiency.
sizing down the rotor will also decrease the stroke, lower the designed efficiency of the engine's torque.
Where i can see a turbo come into play is to replace multiple ports, on high rpm, have a turbo kick in to deliver the necessary amount of air so the engine don't starve for air.
just my 2 cents.
for what it's worth, one time i had a full car and was going on a slight hill (country highway). on 6th gear i was slowing down because i couldn't provide enough torque even WOT and had to downshift to 5th gear.. we really need some torque.
If you think a smaller engine with a turbo wouldn't be adequate, go drive an 87-88 Turbo II RX-7. That car made 182 HP at 6500 rpm and 183 ft lbs of torque at 3000 rpm. It feels like a much larger engine down low than a Renesis despite having 40 or so less hp and the gearing in that car isn't nearly as aggressive.
I don't want to decrease the stroke from current. I want to decrease the width. Torque is determined by displacement. Stroke determines where the torque peak will occur. A longer stroke will give you the torque peak lower in the rpm range and a shorter stroke will give you a torque peak higher in the rpm range. Obviously this is what you want to address as you want that torque peak lower. Refer to the above mentioned TII RX-7 with it's 8.5:1 compression ratio and compare it to a Renesis. That's what the turbo is for. A rotary is most volumetrically efficient at higher rpms. The turbo will give it a wide efficiency range. In na form any engine has a narrower rpm range of efficiency. If you increase the stroke, you will also lower the max rpm. This is fine if we can hold it to 7500-8000 or so but the powerband will still be much narrower and the highest efficiency will still be over a smaller area than with a turbo.
If we had 2 engines, 1 a small engine with a turbo and the other a larger engine without a turbo, and they both made the same peak horsepower, the smaller engine with the turbo would have the wider powerband with the most average power and feel like the larger engine. It would also be more fuel efficient assuming of course the turbo isn't so crappy as to choke the engine to death which unfortunately has been known to happen in the past.
03-09-2010, 11:33 AM
#320
Smaller engine will inherently have smaller surface area, same generated heat, smaller loss... Higher displacement engine will be run at even lower load than current Renesis. Do you know why rotaries have so bad fuel consumption in cars?(it applies to all engines but rotaries for some reason exceptionally). Its due to very high BSFC at low load - main problem ---->throttle valve...
And to all people who have obsession with the stroke, stroke isnīt increasing torque!! Torque is function of BMEP and displacement. If 16x or whatever will produce higher specific torque than Renesis, it will be due to better combustion/heat generation, not increased eccentricity
I thinking of 10A geometry, all aluminium, all side port (just simple 4 port intake, maybe only 2 port exhaust
) and nice simple single turbo
03-09-2010, 11:01 PM
#321
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And to all people who have obsession with the stroke, stroke isnīt increasing torque!! Torque is function of BMEP and displacement. If 16x or whatever will produce higher specific torque than Renesis, it will be due to better combustion/heat generation, not increased eccentricity:
:
03-10-2010, 07:22 AM
#322
Increased eccentricity means smaller surface area to volume ratio which means less heat lost to the cooling system and more of the force of that expansion pushing the rotor. More push, higher BMEP, more torque. The drawback is the increased eccentricity means a more dramatic acceleration of the rotor back and forth over its circular axis. Basically more wobble which means it's more stressful on the components to change direction and power drops off so there's a lower red line.
03-10-2010, 07:40 AM
#323
Momentum Keeps Me Going
I believe the center bearing would be very wise, if not manditory for longevity. It's not the HP so much as the harmonics in the unsupported eshaft that will do it in without one. It's certainly a weak spot and it doesn't have to break to brick the engine. With a measily 232HP NA I was able to *bend* my eshaft, resulting in replacement. The engineering design margins must be fairly thin for that to occur.
03-10-2010, 08:00 AM
#324
I believe the center bearing would be very wise, if not manditory for longevity. It's not the HP so much as the harmonics in the unsupported eshaft that will do it in without one. It's certainly a weak spot and it doesn't have to break to brick the engine. With a measily 232HP NA I was able to *bend* my eshaft, resulting in replacement. The engineering design margins must be fairly thin for that to occur.
.What happened though, did you select too low a gear or something?
Paul.
03-10-2010, 10:45 AM
#325
Momentum Keeps Me Going
no, it happened at a 3rd gear downshift while braking for a corner, but I was not going fast enough to overrev at that point. At that instant I was unable to shift into gear, it was a struggle to do so, so thought it was a transmission/clutch problem, but it wasn't. After that the engine ran strangely and the inspection showed a wobbily (word?) flywheel aka bent eccentric shaft. Stuff happens.