# Auto Exhaust turbine **URL:** \ **Category:** Factual Questions\ **Created:** [October 5, 2012, 5:08pm UTC](https://boards.straightdope.com/t/auto-exhaust-turbine/636824 "2012-10-05T17:08:11Z")\ **Posts on this page:** 17\ **Page:** 1
**Author:** ![hex173t](https://avatars.discourse-cdn.com/v4/letter/h/4da419/32.png) [@hex173t](https://boards.straightdope.com/u/hex173t)\ **Post date:** [October 5, 2012, 5:08pm UTC](https://boards.straightdope.com/t/auto-exhaust-turbine/636824/1 "2012-10-05T17:08:11Z")
Hello all, first question/post I’ve done alittle reading on engines used on old aircraft, like from the 40’s to 50’s, like the DC-7. The engines used a turbine in the exhaust stream to turn a shaft that geared on to the crank shaft, or gearbox, something like that to recover the otherwise lost energy from the exhaust. Is there any reason that no car or truck manufacturers have done this to increase efficiency? Only thing I can think of is that aircraft spend much of the time at middle power settings (60-70%) where there is more exhaust energy to extract, where cars or trucks spend most of the time at lower power settings? Is this why? Thanks ---
**Author:** ![leahcim](https://avatars.discourse-cdn.com/v4/letter/l/b4bc9f/32.png) [@leahcim](https://boards.straightdope.com/u/leahcim)\ **Post date:** [October 5, 2012, 5:09pm UTC](https://boards.straightdope.com/t/auto-exhaust-turbine/636824/2 "2012-10-05T17:09:56Z")
Don’t turbochargers operate off “exhaust power”? ---
**Author:** ![Novelty\_Bobble](https://avatars.discourse-cdn.com/v4/letter/n/a3d4f5/32.png) [@Novelty\_Bobble](https://boards.straightdope.com/u/Novelty_Bobble)\ **Post date:** [October 5, 2012, 5:13pm UTC](https://boards.straightdope.com/t/auto-exhaust-turbine/636824/3 "2012-10-05T17:13:55Z")
Deleted ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [October 5, 2012, 5:17pm UTC](https://boards.straightdope.com/t/auto-exhaust-turbine/636824/4 "2012-10-05T17:17:14Z")
it’s called “turbo compounding,” and it’s done on the Detroit Diesel DD15-TC truck engine. > **[Detroit DD15 Engine | Demand Detroit](https://demanddetroit.com/engines/dd15/)** > > The Detroit® DD15® engine delivers horsepower & torque at lower RPMs, keeping your truck in top gear longer while cruising at more efficient engine speeds. ---
**Author:** ![Hail\_Ants](https://avatars.discourse-cdn.com/v4/letter/h/dc4da7/32.png) [@Hail\_Ants](https://boards.straightdope.com/u/Hail_Ants)\ **Post date:** [October 6, 2012, 5:07am UTC](https://boards.straightdope.com/t/auto-exhaust-turbine/636824/5 "2012-10-06T05:07:58Z")
> [@hex173t](#): > > Is there any reason that no car or truck manufacturers have done this to increase efficiency? Only thing I can think of is that aircraft spend much of the time at middle power settings (60-70%) where there is more exhaust energy to extract, where cars or trucks spend most of the time at lower power settings? Is this why? What you’re describing is called a \*\*turbocharger \*\*and they’ve been used on cars & trucks for decades. Part of the reason they’re not used as much on cars & trucks is as you said, because they function better at a steady RPM. Other reasons include: [ul] [li]As opposed to automobiles, aircraft also have issues regarding air density at altitude that make turbochargers more useful.[/li][li]Turbos are high-precision and expensive pieces of equipment (they run at very high RPMs, over 10,000) that require more attention & maintenance than is usually expected for consumer autos (but not for aircraft).[/li][li]You don’t get something for nothing, the back-pressure of a turbo offsets some of its fuel-efficiency & performance gains. Again, this is less of an issue for aircraft.[/li][/ul] BTW, there is also a similar device called a \*\*supercharger \*\*(or blower) which functions similarly but instead of being powered by exhaust pressure it’s driven by a belt off the crankshaft. Both aircraft & autos use them, but they are much less common than turbos for autos. They give a significantly higher performance boost than turbochargers. ---
**Author:** ![The\_Librarian](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/the_librarian/32/402_2.png) [@The\_Librarian](https://boards.straightdope.com/u/The_Librarian)\ **Post date:** [October 6, 2012, 6:33am UTC](https://boards.straightdope.com/t/auto-exhaust-turbine/636824/6 "2012-10-06T06:33:26Z")
> [@Hail\_Ants](#): > > (snip) They give a significantly higher performance boost than turbochargers. I do not believe this is true. Think about it, a turbo uses energy from the exhaust. A supercharger uses energy from the driveshaft. Now, free energy doesn’t exist, but one of the above is closer to it than the other. Which is why the only manufacturers making supercharged engines are Bentley and Mercedes-Benz, at least those are the only 2 I can think of. And I believe those two use the label ‘supercharged’ and ‘kompressor’ more for historical/marketing reasons than for pure performance or efficiency. That why you’ll never hear about f1 cars or 50 ton trucks being supercharged. ---
**Author:** ![Novelty\_Bobble](https://avatars.discourse-cdn.com/v4/letter/n/a3d4f5/32.png) [@Novelty\_Bobble](https://boards.straightdope.com/u/Novelty_Bobble)\ **Post date:** [October 6, 2012, 6:58am UTC](https://boards.straightdope.com/t/auto-exhaust-turbine/636824/7 "2012-10-06T06:58:14Z")
The OP seems to suggesting the exhaust turbine connects back in to the main shaft, That is not a turbocharger which uses the the energy to compress the fuel/air charge prior to injection into the cylinder. And to Hail Ants, turbo charging has been standard technology for years on diesel engines, both cars and trucks. Small petrol engines (1.2 to 1.4l) are regularly boosted to give power outputs of far larger engines. ---
**Author:** ![RandomLetters](https://avatars.discourse-cdn.com/v4/letter/r/8edcca/32.png) [@RandomLetters](https://boards.straightdope.com/u/RandomLetters)\ **Post date:** [October 6, 2012, 7:37am UTC](https://boards.straightdope.com/t/auto-exhaust-turbine/636824/8 "2012-10-06T07:37:24Z")
> [@The\_Librarian](#): > > I do not believe this is true. > > Think about it, a turbo uses energy from the exhaust. A supercharger uses energy from the driveshaft. Now, free energy doesn’t exist, but one of the above is closer to it than the other. Which is why the only manufacturers making supercharged engines are Bentley and Mercedes-Benz, at least those are the only 2 I can think of. And I believe those two use the label ‘supercharged’ and ‘kompressor’ more for historical/marketing reasons than for pure performance or efficiency. That why you’ll never hear about f1 cars or 50 ton trucks being supercharged. Lots of other companies use superchargers in various cars; Ford uses a supercharger in the Mustang GT500, GM uses them in the Camaro ZL1, Corvette ZR1 & CTS-V, Jaguar/Land Rover use superchargers in a number of products (and will be replacing their naturally aspirated 5.0 v8 with a 3.0 liter supercharged v6 in many of the others soon); other parts of the Volkswagen Auto Group besides Bentley use superchargers; Audi has been replacing their v8s with a supercharged v6 too, and so on. ---
**Author:** ![Richard\_Pearse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/richard_pearse/32/13144_2.png) [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)\ **Post date:** [October 6, 2012, 7:52am UTC](https://boards.straightdope.com/t/auto-exhaust-turbine/636824/9 "2012-10-06T07:52:55Z")
> [@Hail\_Ants](#): > > What you’re describing is called a \*\*turbocharger \*\*and they’ve been used on cars & trucks for decades. No, a turbocharger compresses the fuel/air mixture. The op is talking about something that works like a gas turbine, where the exhaust gasses drive a turbine that is directly connected to the crank. The extra performance is gained with the same fuel consumption, where as a turbocharger increases fuel consumption for its extra performance. **jz78817** is right in calling it a turbo compound engine. [Here](http://en.wikipedia.org/wiki/Turbo-compound_engine) is the wiki page on it. I hadn’t heard of a turbo-compound engine before, interesting stuff, but fairly rare so presumably not the best way of doing things. The wiki entry suggests that the turbine section of these engines were so efficient compared to the reciprocating part, that they were supplanted by pure turbine engines. ---
**Author:** ![coremelt](https://avatars.discourse-cdn.com/v4/letter/c/4491bb/32.png) [@coremelt](https://boards.straightdope.com/u/coremelt)\ **Post date:** [October 6, 2012, 10:11am UTC](https://boards.straightdope.com/t/auto-exhaust-turbine/636824/10 "2012-10-06T10:11:18Z")
> [@The\_Librarian](#): > > That why you’ll never hear about f1 cars or 50 ton trucks being supercharged. Superchargers are currently banned in F1 rules. When they were allowed they were used. the new F1 regs in 2014 are going to allow Turbo-Compounding and it’s expected to be used in competitive engines, so it must make sense from an energy recover standpoint. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [October 6, 2012, 12:28pm UTC](https://boards.straightdope.com/t/auto-exhaust-turbine/636824/11 "2012-10-06T12:28:10Z")
> [@Richard\_Pearse](#): > > No, a turbocharger compresses the fuel/air mixture. The op is talking about something that works like a gas turbine, where the exhaust gasses drive a turbine that is directly connected to the crank. The extra performance is gained with the same fuel consumption, where as a turbocharger increases fuel consumption for its extra performance. **jz78817** is right in calling it a turbo compound engine. [Here](http://en.wikipedia.org/wiki/Turbo-compound_engine) is the wiki page on it. I hadn’t heard of a turbo-compound engine before, interesting stuff, but fairly rare so presumably not the best way of doing things. The wiki entry suggests that the turbine section of these engines were so efficient compared to the reciprocating part, that they were supplanted by pure turbine engines. when you get down to it, a turbocharger _is_ a gas turbine, only one with a whole 'nother engine as its gas generator 😉 ---
**Author:** ![Novelty\_Bobble](https://avatars.discourse-cdn.com/v4/letter/n/a3d4f5/32.png) [@Novelty\_Bobble](https://boards.straightdope.com/u/Novelty_Bobble)\ **Post date:** [October 6, 2012, 3:03pm UTC](https://boards.straightdope.com/t/auto-exhaust-turbine/636824/12 "2012-10-06T15:03:45Z")
> [@jz78817](#): > > when you get down to it, a turbocharger _is_ a gas turbine, only one with a whole 'nother engine as its gas generator 😉 The classic jet engine uses connected turbines, driven by the exhaust to compress the incoming air charge so in high level terms, yes, I suppose it is. ---
**Author:** ![Richard\_Pearse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/richard_pearse/32/13144_2.png) [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)\ **Post date:** [October 6, 2012, 5:21pm UTC](https://boards.straightdope.com/t/auto-exhaust-turbine/636824/13 "2012-10-06T17:21:53Z")
> [@jz78817](#): > > when you get down to it, a turbocharger _is_ a gas turbine, only one with a whole 'nother engine as its gas generator 😉 True. And the turbo-compound engine is very similar in concept to a turbo-shaft. ---
**Author:** ![Hail\_Ants](https://avatars.discourse-cdn.com/v4/letter/h/dc4da7/32.png) [@Hail\_Ants](https://boards.straightdope.com/u/Hail_Ants)\ **Post date:** [October 11, 2012, 3:49am UTC](https://boards.straightdope.com/t/auto-exhaust-turbine/636824/14 "2012-10-11T03:49:29Z")
> [@Richard\_Pearse](#): > > No, a turbocharger compresses the fuel/air mixture. The op is talking about something that works like a gas turbine, where the exhaust gasses drive a turbine that is directly connected to the crank. The extra performance is gained with the same fuel consumption, where as a turbocharger increases fuel consumption for its extra performance. **jz78817** is right in calling it a turbo compound engine. [Here](http://en.wikipedia.org/wiki/Turbo-compound_engine) is the wiki page on it. I hadn’t heard of a turbo-compound engine before, interesting stuff, but fairly rare so presumably not the best way of doing things. The wiki entry suggests that the turbine section of these engines were so efficient compared to the reciprocating part, that they were supplanted by pure turbine engines. Wow, you’re right. I’d never heard of a turbo-compound engine before! Like every kind of turbine engine the main reason they’re not suited for cars is because turbines are designed to run at a constant (and rather high) RPM and power band, and automobiles are simply not driven that way. Just the opposite in fact. It’s also the reason that, battery weight/power issues aside, an electric motor is probably the best prime mover for stop & go transportation (i.e. cars). ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [October 11, 2012, 1:00pm UTC](https://boards.straightdope.com/t/auto-exhaust-turbine/636824/15 "2012-10-11T13:00:56Z")
> [@Hail\_Ants](#): > > Wow, you’re right. I’d never heard of a turbo-compound engine before! Like every kind of turbine engine the main reason they’re not suited for cars is because turbines are designed to run at a constant (and rather high) RPM and power band, and automobiles are simply not driven that way. weeeellll… that’s true for a self-contained gas turbine (i.e. one with its own gas generator section.) In this case, the compounding turbine is not the prime mover, and the gas to drive it comes from another engine which is the prime mover. So it’s not quite the same as a gas turbine engine running at lower than peak power. I think the real reasons it’s not more common is cost and complexity. ---
**Author:** ![Rocketeer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rocketeer/32/4437_2.png) [@Rocketeer](https://boards.straightdope.com/u/Rocketeer)\ **Post date:** [October 11, 2012, 5:56pm UTC](https://boards.straightdope.com/t/auto-exhaust-turbine/636824/16 "2012-10-11T17:56:50Z")
> [@jz78817](#): > > it’s called “turbo compounding,” and it’s done on the Detroit Diesel DD15-TC truck engine. > > [Detroit DD15 Engine | Detroit](http://www.demanddetroit.com/engines/dd15tc/default.aspx) I looked over your link pretty carefully and although they used the words “turbo compounding”, as near as I can tell they’re using a conventional turbocharger in a conventional way. (I would love to be proved wrong, because turbo-compounding is cool.) ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [October 11, 2012, 6:54pm UTC](https://boards.straightdope.com/t/auto-exhaust-turbine/636824/17 "2012-10-11T18:54:23Z")
> [@Rocketeer](#): > > I looked over your link pretty carefully and although they used the words “turbo compounding”, as near as I can tell they’re using a conventional turbocharger in a conventional way. (I would love to be proved wrong, because turbo-compounding is cool.) [This review describes the system](http://www.dieselpowermag.com/features/0802dp_detroit_diesel_dd15_diesel_engine/viewall.html) and there’s definitely turbo-compounding involved, but it sounds like it’s somehow combined with a conventional turbocharger: > [@Diesel Power Mag](#): > > By inventing a new type of turbo compounding system, the DD15 engineers found a way to add 50 hp and still improve fuel economy by 5 percent. The system works by using a conventional Holset HX55 turbo without a wastegate that feeds into a unique “turbo compound axial power turbine” that transfers power directly to the engine flywheel. By scavenging exhaust heat that would normally fly out of the tailpipe, the “axial power turbine” is able to spin a small gearbox that helps create up to 100 lb-ft of torque when the engine is under a full load.