Has turbo compounding ever been tried for automotive engines?
05-31-02 | 12:41 AM
#1
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From: MS Gulf Coast
Has turbo compounding ever been tried for automotive engines?
Just curious, because the rotary seems like a natural for turbo-compounding. It's exhaust is hotter (i.e., contains more energy) than an equivalently powerful piston engine. Yet, it doesn't take to forced injection as readily as other engines because of detonation problems.
In other words, even if you do run a turbo setup, you can't run the high boost levels some engines get away with, so there is still gobs of energy left in the exhaust stream.
With the perfect exahaust stream, and a low rotating mass, I would think some insane person would have tried it. Of course, you'd probably need a trick exhaust valve and bypass system so that the (necessarily) large turbo didn't choke the engine at low rpm's before enough energy became available in the exhaust, and then open up as the power comes up. I think a 6:1 ratio or so for most turbo's would probably work about right.
I wonder why it's not done a Le Mans and other places where fuel consumption is a big concern. Nothing like more horsepower without any extra fuel consumption. I guess it's either too heavy, too unreliable, or just too hard to get worthwile power out of it.
Still, makes me go hmm.......
In other words, even if you do run a turbo setup, you can't run the high boost levels some engines get away with, so there is still gobs of energy left in the exhaust stream.
With the perfect exahaust stream, and a low rotating mass, I would think some insane person would have tried it. Of course, you'd probably need a trick exhaust valve and bypass system so that the (necessarily) large turbo didn't choke the engine at low rpm's before enough energy became available in the exhaust, and then open up as the power comes up. I think a 6:1 ratio or so for most turbo's would probably work about right.
I wonder why it's not done a Le Mans and other places where fuel consumption is a big concern. Nothing like more horsepower without any extra fuel consumption. I guess it's either too heavy, too unreliable, or just too hard to get worthwile power out of it.
Still, makes me go hmm.......
05-31-02 | 01:06 AM
#2
Yellow Dragon is no more
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From: Knoxville, TN
If are refering to staged turbos, then the answer would be yes ... diesel trucks and big tractors do it. It makes very high boost and creates a very narrow power band. Most setups I have seen don't even try to use a wastegated system. Sizing the turbos is almost an art because the turbos interact with each other. One must know the equations to get you in the right ball park-experience is a major factor in getting it to work at all. My diesel friend won't even run a staged setup for less than 50 psi of boost.
05-31-02 | 01:51 AM
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Ah, no (but that would be another interesting one...), let me clarify:
Turbo-compounding was used on some aircraft engines, starting back in the WWII days I believe. It involves a rather large turbo that doesn't spin a compressor, but rather is mechanically connected back to the crankshaft using a geared reduction.
If you took a big jumbo diesel turbo that took, say, 100hp out of the exhaust stream, you could in theory run the turbine through a gear reduction back into the crank and have 100 extra crank hp without any extra fuel or any higher compression ratio (boost).
It would put more back pressure in the exhaust stream, but I think the extra power would be worth it. As I pointed out, you wouldn't want that big honking thing in the exhaust stream at low rev's, so you'd need a bypass system in the exhaust plumbing that started diverting the stream throught the turbine as the power came up. At high rpm's, the thing would be making decent power.
Certainly not the road to a broad flat torque curve, but hell... if it doesn't cost you any extra fuel or engine wear and tear, why not?
The beauty is that you could run a NA high compression engine, and use turbo compounding to recover lost exhaust energy instead of turbocharging. Or, run low boost and use the compounding as a bonus.
Like I said, the only drawbacks I can think of is weight, complexity, and backpressure. The second is solvable. People running high boost live with the third already.
How much does a really big freaking turbo weigh, and how much of that is the compressor part? I'd guess a gear reduction would probably be somewhat close to the compressor in weight, so that would give a decent idea of the package weight.
Anyone know how much power it takes to spool up a diesel turbo?
Turbo-compounding was used on some aircraft engines, starting back in the WWII days I believe. It involves a rather large turbo that doesn't spin a compressor, but rather is mechanically connected back to the crankshaft using a geared reduction.
If you took a big jumbo diesel turbo that took, say, 100hp out of the exhaust stream, you could in theory run the turbine through a gear reduction back into the crank and have 100 extra crank hp without any extra fuel or any higher compression ratio (boost).
It would put more back pressure in the exhaust stream, but I think the extra power would be worth it. As I pointed out, you wouldn't want that big honking thing in the exhaust stream at low rev's, so you'd need a bypass system in the exhaust plumbing that started diverting the stream throught the turbine as the power came up. At high rpm's, the thing would be making decent power.
Certainly not the road to a broad flat torque curve, but hell... if it doesn't cost you any extra fuel or engine wear and tear, why not?
The beauty is that you could run a NA high compression engine, and use turbo compounding to recover lost exhaust energy instead of turbocharging. Or, run low boost and use the compounding as a bonus.
Like I said, the only drawbacks I can think of is weight, complexity, and backpressure. The second is solvable. People running high boost live with the third already.
How much does a really big freaking turbo weigh, and how much of that is the compressor part? I'd guess a gear reduction would probably be somewhat close to the compressor in weight, so that would give a decent idea of the package weight.
Anyone know how much power it takes to spool up a diesel turbo?
05-31-02 | 03:04 AM
#5
Yellow Dragon is no more
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From: Knoxville, TN
I get what you are saying now. I'm going to need some time to chew on the idea and kick it around with some friends. I'm just not sure how much force you could add to the eccentric shaft using this method. A rotary engine turns over pretty easy as is.
Big turbos can weight 40 to 50 lbs .... medium turbos are probably more in the range of 25 lbs. (I'm using memory of holding them in my hands as an estimate so don't shoot me please!) I'd also say most of the weight seems to be in the housings so you would same some weight from the compressor housing.
I know how much power it takes to spool a turbo in a diesel say, but I'm not allowed to say. Those diesel guys are SO SO worried and secret with their info. As a matter of fact their really aren't that many people who know how to correctly stage turbos so they don't want anyone else finding out. Some guys at truck and tractor pulls will not open their hood and if you try to peak you are liable to get shot!
Big turbos can weight 40 to 50 lbs .... medium turbos are probably more in the range of 25 lbs. (I'm using memory of holding them in my hands as an estimate so don't shoot me please!) I'd also say most of the weight seems to be in the housings so you would same some weight from the compressor housing.
I know how much power it takes to spool a turbo in a diesel say, but I'm not allowed to say. Those diesel guys are SO SO worried and secret with their info. As a matter of fact their really aren't that many people who know how to correctly stage turbos so they don't want anyone else finding out. Some guys at truck and tractor pulls will not open their hood and if you try to peak you are liable to get shot!
05-31-02 | 10:22 AM
#6
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From: MS Gulf Coast
Since you're not compressing air to high pressure levels, then the requirement on structrual integrity of the housing is decreased. I think the gearset required would weight about what the compressor does, so let's use your rough figures to play the "what if" game.
If a 50 pound turbo could be dissasembled, the turbine mated with a gearset and new housing, and connected to the crankshaft or e-shaft to provide 100 absolutely free hp, would it be worth it?
That's 2 pounds per horsepower, which would drag the average of most any car up, not down. Hell, even a 1000hp RX-7 beast has more than 2 pounds per horsepower. The way I see it (unless these "guesses" are way off) is that it shoud help the power to weight ratio or practically any car.
It would seem to be most attractive to stock engines though, since it is a way of increasing power in a small engine without any effect at all on emissions or fuel economy.
So, what's the snag that's kept it from being tried???
If a 50 pound turbo could be dissasembled, the turbine mated with a gearset and new housing, and connected to the crankshaft or e-shaft to provide 100 absolutely free hp, would it be worth it?
That's 2 pounds per horsepower, which would drag the average of most any car up, not down. Hell, even a 1000hp RX-7 beast has more than 2 pounds per horsepower. The way I see it (unless these "guesses" are way off) is that it shoud help the power to weight ratio or practically any car.
It would seem to be most attractive to stock engines though, since it is a way of increasing power in a small engine without any effect at all on emissions or fuel economy.
So, what's the snag that's kept it from being tried???
05-31-02 | 10:25 AM
#7
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From: MS Gulf Coast
Remember, in most engines there's approximately as much energy going out the exhaust stream as there is going to the crank (more so in rotary engines).
A 500hp engine has 500hp of "free" energy in the exhaust. Turbo-compounding is a way of reclaiming some of that without fuel economy or engine wear penalties.
A 500hp engine has 500hp of "free" energy in the exhaust. Turbo-compounding is a way of reclaiming some of that without fuel economy or engine wear penalties.
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05-31-02 | 11:06 AM
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Originally posted by Freaky Monkey007
I hate to sound stupid but i dont fully understand what turbo compounding is.. Can someone plz explain?
I hate to sound stupid but i dont fully understand what turbo compounding is.. Can someone plz explain?
05-31-02 | 11:56 AM
#10
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Yes, exactly. The exhaust gas stream spins a turbine, which then has available power to either compress air for a forced induction system, or do something else.
In turbo compounding, you do something else. Specifically, you take the power produced from the turbine and mechanically couple it to the crankshaft (perhaps using a fluid coupling to isolate crank torque pulses from the turbine).
It just seems to me that the rotary is the perfect engine to use as a testbed, if the technical problems can be overcome. Rotaries have lots of hot exahust energy to do something with, and you can't readily reinforce and modify a rotary for high psi boost levels like piston engines... so you can't use much of that exhaust energy for forced air compression.
In turbo compounding, you do something else. Specifically, you take the power produced from the turbine and mechanically couple it to the crankshaft (perhaps using a fluid coupling to isolate crank torque pulses from the turbine).
It just seems to me that the rotary is the perfect engine to use as a testbed, if the technical problems can be overcome. Rotaries have lots of hot exahust energy to do something with, and you can't readily reinforce and modify a rotary for high psi boost levels like piston engines... so you can't use much of that exhaust energy for forced air compression.
05-31-02 | 01:21 PM
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Originally posted by Bigus Dickus
Yes, exactly. The exhaust gas stream spins a turbine, which then has available power to either compress air for a forced induction system, or do something else.
In turbo compounding, you do something else. Specifically, you take the power produced from the turbine and mechanically couple it to the crankshaft (perhaps using a fluid coupling to isolate crank torque pulses from the turbine).
It just seems to me that the rotary is the perfect engine to use as a testbed, if the technical problems can be overcome. Rotaries have lots of hot exahust energy to do something with, and you can't readily reinforce and modify a rotary for high psi boost levels like piston engines... so you can't use much of that exhaust energy for forced air compression.
Yes, exactly. The exhaust gas stream spins a turbine, which then has available power to either compress air for a forced induction system, or do something else.
In turbo compounding, you do something else. Specifically, you take the power produced from the turbine and mechanically couple it to the crankshaft (perhaps using a fluid coupling to isolate crank torque pulses from the turbine).
It just seems to me that the rotary is the perfect engine to use as a testbed, if the technical problems can be overcome. Rotaries have lots of hot exahust energy to do something with, and you can't readily reinforce and modify a rotary for high psi boost levels like piston engines... so you can't use much of that exhaust energy for forced air compression.
06-01-02 | 05:41 AM
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Hmmmm... very interesting...
I found this on Road and Track's Website...
------------------------------------------------------------------------
Compound Glory
Recently I read about the remarkable Wright R-3350 Turbo-Compound aircraft engine that had three turbocharger-like turbines that were connected via clutches directly to the crankshaft. In its final form this engine produced 3700 bhp from its 18 cylinders, up from 2700 bhp of the original Cyclone. Has this technique ever been tried on auto engines? It seems that a V-type engine with a turbine off each bank of cylinders plus a mechanically driven supercharger would really be something.
P. Houston
Ottawa, Ontario, Canada
No doubt the R-3350 was one of the greatest aircraft piston engines to ever swing a prop, and, interestingly, neither Wright, nor arch rival Pratt & Whitney, nor any of several other aircraft engine builders worldwide, employed turbo-compounding on other engines. The technique, which apparently is unique to the big Cyclone, came along at the dawn of the turbine age, and thus the end of large-displacement piston-engine development. Wright Aeronautical calculated the Turbo-Compound feature was worth 550 bhp on the R-3350, which was also centrifugally supercharged.
Several aspects of turbo-compounding do not lend themselves to automotive use. It's mechanically complex, with most of the disadvantages of turbocharging (costly turbines, heat retention, packaging problems, exhaust obstruction), plus the mechanical intricacies found around the crankshaft. All told, the Turbo-Compound feature added 540 lb. to the R-3350. Furthermore, it seems doubtful the always-varying rpm of an auto engine is suited to the geartrain and clutches, whereas the big Cyclone was employed in multi-engine aircraft where relatively few rpm changes were encountered.
Finally, while your blown and Turbo-Compound V-type engine would clearly thunder out plenty of power, no doubt even greater power could be realized without the complexity of turbo-compounding, which is one way of recouping energy otherwise lost as exhaust heat. Turbocharging is another such method. In fact, the current F8F Bearcat air racer, Rare Bear, employs a non-Turbo-Compound R-3350. It is boosted by centrifugal supercharging and nitrous-oxide injection, but the exhaust runs freely to the atmosphere.
------------------------------------------------------------------------
I found this on Road and Track's Website...
------------------------------------------------------------------------
Compound Glory
Recently I read about the remarkable Wright R-3350 Turbo-Compound aircraft engine that had three turbocharger-like turbines that were connected via clutches directly to the crankshaft. In its final form this engine produced 3700 bhp from its 18 cylinders, up from 2700 bhp of the original Cyclone. Has this technique ever been tried on auto engines? It seems that a V-type engine with a turbine off each bank of cylinders plus a mechanically driven supercharger would really be something.
P. Houston
Ottawa, Ontario, Canada
No doubt the R-3350 was one of the greatest aircraft piston engines to ever swing a prop, and, interestingly, neither Wright, nor arch rival Pratt & Whitney, nor any of several other aircraft engine builders worldwide, employed turbo-compounding on other engines. The technique, which apparently is unique to the big Cyclone, came along at the dawn of the turbine age, and thus the end of large-displacement piston-engine development. Wright Aeronautical calculated the Turbo-Compound feature was worth 550 bhp on the R-3350, which was also centrifugally supercharged.
Several aspects of turbo-compounding do not lend themselves to automotive use. It's mechanically complex, with most of the disadvantages of turbocharging (costly turbines, heat retention, packaging problems, exhaust obstruction), plus the mechanical intricacies found around the crankshaft. All told, the Turbo-Compound feature added 540 lb. to the R-3350. Furthermore, it seems doubtful the always-varying rpm of an auto engine is suited to the geartrain and clutches, whereas the big Cyclone was employed in multi-engine aircraft where relatively few rpm changes were encountered.
Finally, while your blown and Turbo-Compound V-type engine would clearly thunder out plenty of power, no doubt even greater power could be realized without the complexity of turbo-compounding, which is one way of recouping energy otherwise lost as exhaust heat. Turbocharging is another such method. In fact, the current F8F Bearcat air racer, Rare Bear, employs a non-Turbo-Compound R-3350. It is boosted by centrifugal supercharging and nitrous-oxide injection, but the exhaust runs freely to the atmosphere.
------------------------------------------------------------------------
06-01-02 | 06:50 AM
#14
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From: Windsor, CA
Someone wants to compound a 20B for aviation use.
http://home.earthlink.net/~rotaryeng/sum-turbo-comp.txt
Quite a few cool pics, etc.
http://home.earthlink.net/~rotaryeng/ACRE.html
http://home.earthlink.net/~rotaryeng/sum-turbo-comp.txt
Quite a few cool pics, etc.
http://home.earthlink.net/~rotaryeng/ACRE.html
06-01-02 | 07:02 AM
#15
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From: Cleveland, Ohio, USA
I don't get it. I mean, I understand the principle, but I don't see the point.
Take an engine that is mechanically supercharged, and stick turbines in the exhaust, which are clutched and geared so that they apply power to the crank.
Why not just drive the supercharger from the turbines? As in, you know, a regular ol' turbocharger?
I don't think it would work too well on a N/A rotary... rotaries HATE exhaust restriction.
Take an engine that is mechanically supercharged, and stick turbines in the exhaust, which are clutched and geared so that they apply power to the crank.
Why not just drive the supercharger from the turbines? As in, you know, a regular ol' turbocharger?
I don't think it would work too well on a N/A rotary... rotaries HATE exhaust restriction.
06-01-02 | 07:16 AM
#16
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From: Windsor, CA
With a car application, I don't think that it makes a lot of sense, just because the load is not as constant. With an aviation app, it can mean more power without any additional fuel or load on the engine.
06-01-02 | 04:46 PM
#17
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Interesting feeback. At least other people have kicked the idea around before. It does make more sense for a constant rpm aircraft engine.
However, with a fluid coupling and an ECU controlled exhaust bypass valve, I think it could add torque to the crank under varying power and rpm ranges without self destructing or anything else terrible happening.
Why you ask? What's the point? Why not just turbocharge?
Well, put simply, how much boost can an engine block take? More importantly to you guys, how much boost can a rotary engine take? 20psi? How much exhaust energy (power) does it take to spool a turbocharger up to full 20psi boost? 50hp maybe?
Just to use nice round hypothetical numbers to illustrate the point, let's say the engine is putting out 500hp (13b) at 20psi boost. No more boost will help, it will just make a nice bomb. The turbo is drawing 50hp out of the exhaust. With a typical engine at 500hp, there's ~500hp going out the tailpipe, more for rotaries. So, even after drawing out as much energy as you can for forced induction (because you can't use any more), you still have ~500hp going out the tailpipe.
Why not just use the exhaust to turn the supercharger (i.e., turbocharging)? Simply because there's a whole lot more power available in the exhaust stream than any engine can possibly make use of for forced induction.
Turbo-compounding is about the only other way of recovering that wasted energy.
OK, so it's heavy. And it's complex. And it will likely self destruct in a short period of time. And it will be expensive.
When has that ever stopped anyone?
Bah, I've got an engineering degree... in my spare time I'll see if I can come up with a lightweight way of doing it.
However, with a fluid coupling and an ECU controlled exhaust bypass valve, I think it could add torque to the crank under varying power and rpm ranges without self destructing or anything else terrible happening.
Why you ask? What's the point? Why not just turbocharge?
Well, put simply, how much boost can an engine block take? More importantly to you guys, how much boost can a rotary engine take? 20psi? How much exhaust energy (power) does it take to spool a turbocharger up to full 20psi boost? 50hp maybe?
Just to use nice round hypothetical numbers to illustrate the point, let's say the engine is putting out 500hp (13b) at 20psi boost. No more boost will help, it will just make a nice bomb.
The turbo is drawing 50hp out of the exhaust. With a typical engine at 500hp, there's ~500hp going out the tailpipe, more for rotaries. So, even after drawing out as much energy as you can for forced induction (because you can't use any more), you still have ~500hp going out the tailpipe.Why not just use the exhaust to turn the supercharger (i.e., turbocharging)? Simply because there's a whole lot more power available in the exhaust stream than any engine can possibly make use of for forced induction.
Turbo-compounding is about the only other way of recovering that wasted energy.
OK, so it's heavy. And it's complex. And it will likely self destruct in a short period of time. And it will be expensive.
When has that ever stopped anyone?
Bah, I've got an engineering degree... in my spare time I'll see if I can come up with a lightweight way of doing it.
06-03-02 | 11:47 PM
#19
Eats, Sleeps, Dreams Rotary
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From: Stinson Beach, Ca
http://home.earthlink.net/~rotaryeng/rb3rot1.jpg
http://home.earthlink.net/~rotaryeng/rb3rot2.jpg
Or maybe not, but it has a compressor on the E-shaft lol
btw, thats the 900hp Racing Beat 20b
http://home.earthlink.net/~rotaryeng/rb3rot2.jpg
Or maybe not, but it has a compressor on the E-shaft lol
btw, thats the 900hp Racing Beat 20b
06-06-02 | 12:21 PM
#23
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From: Windsor, CA
Originally posted by turbostreetfighter
ummm guys....that is a water pump!! look where the outlet leads to.
ummm guys....that is a water pump!! look where the outlet leads to.
When I first looked at that pic, I was like that could be an example of turbo compounding. I think that the front cover plate for the dry sump makes the assembly look like there could be gearing to the e-shaft in there, too. It is a water pump though.
06-06-02 | 01:32 PM
#24
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From: Naugatuck, CT
I have an Idea how about we run the exhaust through a heat exchanger. use it to boil water and use the steam to run a turbine which would be connected to the crank through some sort of transmission wich would be geared base on the rpms the engine is running and thus minimizing its effect on back preassure in the ehhaust system. Just an idea. 
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