why is the rotary so inefficient??
11-23-02, 01:34 AM
#51
The ratio of combustion chamber surface area to volume is large on the rotary, so you lose more of the combustion energy to the cooling system. The "new surfaces" explanation seems like it would also be a significant part of the increased loss of energy to the cooling system vs. piston engines.
Other NA engines that make >100 HP/L (more than the Renesis):
- E46 M3
- Ferrari 360 Modena
-Max
Other NA engines that make >100 HP/L (more than the Renesis):
- E46 M3
- Ferrari 360 Modena
-Max
11-23-02, 11:58 AM
#52
Full Member
Join Date: Jan 2002
Location: Marietta, GA
Posts: 100
Likes: 0
Received 0 Likes
on
0 Posts
Originally posted by Orange!FD
Well HELL. You're right about combustions/rev, Kevin. And thanks for the description of how to arrive at the 2.6l often used as a comparison to boingers, and about where the wankel makes up what would otherwise be a severe torque deficit.
And sorry about the rant, to Buger.
/gets cold crow from fridge for late night snack.
Well HELL. You're right about combustions/rev, Kevin. And thanks for the description of how to arrive at the 2.6l often used as a comparison to boingers, and about where the wankel makes up what would otherwise be a severe torque deficit.
And sorry about the rant, to Buger.
/gets cold crow from fridge for late night snack.
Don't worry about it although I'd like to think that most people can tell that I usually don't shoot my mouth off without at least glancing at something and giving it a little thought.Brian
11-23-02, 12:13 PM
#53
Full Member
Join Date: Jan 2002
Location: Marietta, GA
Posts: 100
Likes: 0
Received 0 Likes
on
0 Posts
Originally posted by KevinK2
Better study that link more. Brian is correct, each rotor fires once per crank/eccentric rev. Rotor spins slower than crank, takes 3 crank revs for one rotor rev, so ea rotor will fire all 3 faces in 3 crank revs.
...afaik, 250 hp for the new engine is only beat by the 240 hp 2L S2000, regarding hp/L for na production engine.
Better study that link more. Brian is correct, each rotor fires once per crank/eccentric rev. Rotor spins slower than crank, takes 3 crank revs for one rotor rev, so ea rotor will fire all 3 faces in 3 crank revs.
...afaik, 250 hp for the new engine is only beat by the 240 hp 2L S2000, regarding hp/L for na production engine.
Originally posted by maxcooper
...Other NA engines that make >100 HP/L (more than the Renesis):
- E46 M3
- Ferrari 360 Modena
-Max
...Other NA engines that make >100 HP/L (more than the Renesis):
- E46 M3
- Ferrari 360 Modena
-Max
There are a few other engines out there that may produce more hp/l than the renesis but we will have to see what the compression ratio on the renesis is before we can really compare them.
One of the easiest ways to increase the thermal efficiency of an engine is to increase the compression ratio. The s2000, e46 M3 and the Ferrari 360 Modena all have engines with compression ratios of at least 11:1. (I believe the e46 M3 has some reliability problems?)
Mazda has not released anything that I could find that explicitly stated the compression ratio of the renesis. They mention that it is "high". I assume that they have increased it over the 9.7:1 of the early 90's na. One limiting factor is the reliability and efficiency of the apex seals. Mazda may have made changes to optimize the apex seal design since there will no longer be any ports on the peripheral housing.
I find myself wondering where the original poster in this discussion went. I hope he wasn't just a troll but he did start an interesting discussion on the engine that may help people understand it more.
Brian
11-24-02, 04:56 PM
#54
WingmaN
Join Date: Aug 2002
Location: Fort Worth Texas
Posts: 4,324
Likes: 0
Received 0 Likes
on
0 Posts
Factor in the horsepower to weight ratio of these motors also. I think that is a more fair comparison since pistons and rotors are comparing apples and oranges. The RX8 produces 247 horsepower. I don't know what the motor weighs, but it would be nice to know. I am sure that we kick the hell out of piston engines in the HP to weight ratio though. Just imagine if the side plates were aluminum.
11-24-02, 11:57 PM
#55
Full Member
Join Date: Oct 2002
Location: Adelaide, Australia
Posts: 107
Likes: 0
Received 0 Likes
on
0 Posts
wow, cant even be bothered reading all this thread
inefficient? damn 1146cc pushes my car up and over 100MPH easily, and its a pretty much standard 78/79 RX-7. my 1.3L 4 cyl mazda has maybe an absolute topspeed around 100MPH
oh yeah, also know that the eccentricity of the shaft is only 15mm, meaning that the stroke is only 15mm, no wonder they dont make much torque.
inefficient? damn 1146cc pushes my car up and over 100MPH easily, and its a pretty much standard 78/79 RX-7. my 1.3L 4 cyl mazda has maybe an absolute topspeed around 100MPH
oh yeah, also know that the eccentricity of the shaft is only 15mm, meaning that the stroke is only 15mm, no wonder they dont make much torque.
11-25-02, 01:53 AM
#56
Originally posted by Rota_Motor
wow, cant even be bothered reading all this thread
inefficient? damn 1146cc pushes my car up and over 100MPH easily, and its a pretty much standard 78/79 RX-7. my 1.3L 4 cyl mazda has maybe an absolute topspeed around 100MPH
oh yeah, also know that the eccentricity of the shaft is only 15mm, meaning that the stroke is only 15mm, no wonder they dont make much torque.
wow, cant even be bothered reading all this thread
inefficient? damn 1146cc pushes my car up and over 100MPH easily, and its a pretty much standard 78/79 RX-7. my 1.3L 4 cyl mazda has maybe an absolute topspeed around 100MPH
oh yeah, also know that the eccentricity of the shaft is only 15mm, meaning that the stroke is only 15mm, no wonder they dont make much torque.
-Max
11-25-02, 03:35 PM
#57
Rotary Enthusiast
thermal inefficiency
comparo with '2.6L' 944 4 cyl. I assumed spherical comb'n chamber, enlarged for same FD 9.0 compr ratio. adjusted bore and stroke from oem 2.5L, to get 2.6L with same bore/stroke ratio.
for FD rotor, R=105mm, and w=80mm. 40 cu-in face displacement. Determined contour radius is 7.67", and found larger radius for 5 cu-in chamber, then radius for 40 cu in displacement from there. also checked using flat chamber assumption ... about same results. I think the approximation of the chamber in the housing as a constant radius should be close enough for a comparo. Here are calc'd heat exchange areas, in sq inches:
944 ___ FD __ % more FD
Total @TDC
26.9 __ 51.0 __ 90%
Total @BDC
66.8 __ 86.1 __ 29%
NEW area @ BDC
39.9 __ 61.5 __ 54%
When things are the hottest near TDC, the area issue is the worst. Also a time factor. The rotary stroke is during 3/4 crank rev. while 944 is only 1/2 rev. The rotary will allow more time for heat exchange, unless typical rpms are 50% higher.
The 944 is a convenient comparo, as it fires 2 pistons per rev, and the rx7s fire 2 rotor faces per crank rev.
" ... eccentricity of the shaft is only 15mm, meaning that the stroke is only 15mm, no wonder they dont make much torque."
The effective stroke is closer to 3 x e.
comparo with '2.6L' 944 4 cyl. I assumed spherical comb'n chamber, enlarged for same FD 9.0 compr ratio. adjusted bore and stroke from oem 2.5L, to get 2.6L with same bore/stroke ratio.
for FD rotor, R=105mm, and w=80mm. 40 cu-in face displacement. Determined contour radius is 7.67", and found larger radius for 5 cu-in chamber, then radius for 40 cu in displacement from there. also checked using flat chamber assumption ... about same results. I think the approximation of the chamber in the housing as a constant radius should be close enough for a comparo. Here are calc'd heat exchange areas, in sq inches:
944 ___ FD __ % more FD
Total @TDC
26.9 __ 51.0 __ 90%
Total @BDC
66.8 __ 86.1 __ 29%
NEW area @ BDC
39.9 __ 61.5 __ 54%
When things are the hottest near TDC, the area issue is the worst. Also a time factor. The rotary stroke is during 3/4 crank rev. while 944 is only 1/2 rev. The rotary will allow more time for heat exchange, unless typical rpms are 50% higher.
The 944 is a convenient comparo, as it fires 2 pistons per rev, and the rx7s fire 2 rotor faces per crank rev.
" ... eccentricity of the shaft is only 15mm, meaning that the stroke is only 15mm, no wonder they dont make much torque."
The effective stroke is closer to 3 x e.
hey pistons, take this 
11-26-02, 08:39 PM
#59
Newbie
Thread Starter
Join Date: Nov 2002
Location: NW IL
Posts: 0
Likes: 0
Received 0 Likes
on
0 Posts
I've created a monster. I'm no troll, I have an RX-7, an 81, but it's dead at the moment. That's why I came here. I went deer hunting over the weekend and they moved my thread, I just found it today.
I would most likely compare the wankel to a piston port two stroke. They use ungodly amounts of fuel, are noisy, hard to tune......but man will they knock your socks off for the size, weight, and displacement.
If you guy know anything about the older Kawasaki two strokes, they played with a rotary valve. I think this would benefit the wankel. It's a rotating plate with holes that allign with the ports. At lower RPMs the holes are less alligned and less air/fuel can enter the motor. As you rev it up the holes allign closer untill being fully alligned at WOT.
Just a thought.
I would most likely compare the wankel to a piston port two stroke. They use ungodly amounts of fuel, are noisy, hard to tune......but man will they knock your socks off for the size, weight, and displacement.
If you guy know anything about the older Kawasaki two strokes, they played with a rotary valve. I think this would benefit the wankel. It's a rotating plate with holes that allign with the ports. At lower RPMs the holes are less alligned and less air/fuel can enter the motor. As you rev it up the holes allign closer untill being fully alligned at WOT.
Just a thought.
11-30-02, 03:20 PM
#61
Eats, Sleeps, Dreams Rotary
iTrader: (1)
Join Date: Jun 2001
Location: London, Ontario, Canada
Posts: 3,106
Likes: 0
Received 0 Likes
on
0 Posts
Originally posted by Buger
The miller cycle was specifically made to reduce pumping losses. Which company put the miller cycle into a production car? I know that the miller cycle rotary was supposed to be a near future design in the 90s.
The miller cycle was specifically made to reduce pumping losses. Which company put the miller cycle into a production car? I know that the miller cycle rotary was supposed to be a near future design in the 90s.
Regarding the other stuff. How about comparing renesis to a Honda 3.0L V6 or Nissan 3.5L? Higher power output, worse gas millage. Not to mention the traditional rotary benifits. In terms of raw power the 3.5Ls with the hotter cams produce more raw power, but not power/litre. Not to mention the have been complaints/issues/etc. with the 3.5Ls not producing numbers consistant with the claimed power.
Go back to the 60s. Rotary power and millage were similar to a big V8.
12-01-02, 09:42 PM
#62
Junior Member
Join Date: Nov 2002
Location: Sydney
Posts: 8
Likes: 0
Received 0 Likes
on
0 Posts
Every turn of a 13B crank it "burns" 1.3ltrs of mixture.
Every turn of a 2.6 litre (4 cylinder) piston motor crank, it burns 1.3 litre of mixture.
Do you see where the comparison comes from now ?
As said before, inefficiency comes from combustion chamber shape.
Power to weight (and size) ratio's are good tho'.
Every turn of a 2.6 litre (4 cylinder) piston motor crank, it burns 1.3 litre of mixture.
Do you see where the comparison comes from now ?
As said before, inefficiency comes from combustion chamber shape.
Power to weight (and size) ratio's are good tho'.
12-03-02, 04:52 AM
#63
Rotary Enthusiast
Join Date: May 2002
Location: San Diego
Posts: 971
Likes: 0
Received 0 Likes
on
0 Posts
Originally posted by Project RX-7
Would the 3 spark engine ( 26B ) be more efficient than a 2 spark 13B ?
Another reson why rotaries are not on par with the piston engines is because piston engines have been around for more than 100 years and thousands of companies and hundreds of car manifacturers spent trillions of dollars in research on it.
Where the rotary was only here for 1/2 the time the pistonsengines have and all the big companies gave up on it because they already had a powerplant to work with. In reeality MAzda was the only car company to stick and research the rotary engine .... and they have been in a not so favorable finacial situation.
Think where the rotary engine would be if it had the same time and research put into it.
Would the 3 spark engine ( 26B ) be more efficient than a 2 spark 13B ?
Another reson why rotaries are not on par with the piston engines is because piston engines have been around for more than 100 years and thousands of companies and hundreds of car manifacturers spent trillions of dollars in research on it.
Where the rotary was only here for 1/2 the time the pistonsengines have and all the big companies gave up on it because they already had a powerplant to work with. In reeality MAzda was the only car company to stick and research the rotary engine .... and they have been in a not so favorable finacial situation.
Think where the rotary engine would be if it had the same time and research put into it.
)
12-12-02, 09:23 PM
#66
Rotary Freak
iTrader: (1)
Join Date: Nov 2002
Location: Glyndon MN
Posts: 1,660
Likes: 0
Received 0 Likes
on
0 Posts
2 H.P. Per cube very efficent
Rotarys are very efficent a 91 N/A for example puts out around 160 HP and is around 80 CI. That is bone stock from the factory. Thats about 2 HP a cube. If piston engines were even close to that efficency level a 91 camaro with a 350 would be putting out over 700 H.P bone stock from the factory and I think in 91 a camaro with a 350 CI was putting out around 245 HP. So I guess I am not getting how the piston engine engine is more efficent? Please explain. Is it because the rotary is a thirsty little motor? Or what? Power costs fuel always. More Power usually means more fuel no matter what size engine.
12-12-02, 10:25 PM
#67
Rotary Enthusiast
Join Date: Feb 2001
Location: Huntington Beach, CA, USA
Posts: 1,025
Likes: 0
Received 4 Likes
on
4 Posts
We're talking about thermal efficiency, you're talking about specific output, two very different things. The closest layman's analogy to thermal efficiency is fuel mileage, so in simple terms, we're trying to explain using physics why rotaries are fuel inefficient. If you don't care about fuel mileage, feel free to move along .
.
12-14-02, 03:01 PM
#68
Rotary Enthusiast
1 H.P. Per cube, not bad
Originally posted by usmcjsy
Rotarys are very efficent a 91 N/A for example puts out around 160 HP and is around 80 CI. That is bone stock from the factory. Thats about 2 HP a cube................
Rotarys are very efficent a 91 N/A for example puts out around 160 HP and is around 80 CI. That is bone stock from the factory. Thats about 2 HP a cube................
12-14-02, 10:20 PM
#69
I am the Anti-Ch(rice)t
Join Date: Nov 2001
Location: Savannah, GA
Posts: 1,363
Likes: 0
Received 0 Likes
on
0 Posts
i dont think anybody has pointed out that the 13B slings fuel out of a large hole in the peripheral of its housing. the renesis fixes this and i have heard numbers of 32% more efficient.... still no torque though
Justin
Justin
12-14-02, 11:54 PM
#70
Where should this fuel go, if not out "a large hole in the peripheral of its housing"? There wouldn't *be* any fuel there if the rotary were better at burning the air/fuel charge.
12-15-02, 03:47 AM
#71
Rotary Enthusiast
Join Date: Feb 2001
Location: Huntington Beach, CA, USA
Posts: 1,025
Likes: 0
Received 4 Likes
on
4 Posts
The shape of the combustion chamber makes it really difficult to get a complete burn. The flame front has to travel a long ways. If you read the SAE paper on the renesis, the side ports allow the chamber to act as a centrafuge, the heavier unburnt fuel is pushed to the very periphery of the housing. By placing the exhaust port slighly toward the center, the unburnt fuel is actually swept past the exhaust port and stays in the chamber to be burned in the next cycle, while still allowing the exhaust gases to exit efficiently. Its genius imho, such an awesome idea and only possible with a rotary.
12-15-02, 04:31 PM
#72
Full Member
Join Date: Jun 2002
Location: northern VA
Posts: 101
Likes: 0
Received 0 Likes
on
0 Posts
Originally posted by Protege Menace
2.6 liters? um try 1.3, this aint no p1st0n engine
2.6 liters? um try 1.3, this aint no p1st0n engine
12-15-02, 04:54 PM
#75
I am the Anti-Ch(rice)t
Join Date: Nov 2001
Location: Savannah, GA
Posts: 1,363
Likes: 0
Received 0 Likes
on
0 Posts
Orange,
most engines dont burn all of their fuel completely. if you lean the engine out so that it does, you risk predetonation. due to the fact that during the explosion on the powerstroke of a rotary, it is actually burning its way out of the motor, not all of the fuel can be burnt, nor should be burnt, before the exhaust port "opens". the renesis (as previously stated) allows the ports to open, yet doesnt dump out the excess fuel
justin
most engines dont burn all of their fuel completely. if you lean the engine out so that it does, you risk predetonation. due to the fact that during the explosion on the powerstroke of a rotary, it is actually burning its way out of the motor, not all of the fuel can be burnt, nor should be burnt, before the exhaust port "opens". the renesis (as previously stated) allows the ports to open, yet doesnt dump out the excess fuel
justin