# A question about my new fascination with Stirling Engines. **URL:** \ **Category:** Factual Questions\ **Created:** [January 27, 2008, 4:30pm UTC](https://boards.straightdope.com/t/a-question-about-my-new-fascination-with-stirling-engines/435197 "2008-01-27T16:30:02Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![enipla](https://avatars.discourse-cdn.com/v4/letter/e/54ee81/32.png) [@enipla](https://boards.straightdope.com/u/enipla)\ **Post date:** [January 27, 2008, 4:30pm UTC](https://boards.straightdope.com/t/a-question-about-my-new-fascination-with-stirling-engines/435197/1 "2008-01-27T16:30:02Z")
But first, a link to a [Wiki](http://en.wikipedia.org/wiki/Stirling_engine)article that the ladies might want to see. Okydok. These engines run on a differential of temperature. As little as a few degrees. That got me thinking. Your basic internal combustion engine makes a great deal of heat. Much of this heat is wasted and controlled by the radiator. We now have hybrids. Batteries are charged when braking or directly from the engine itself. Why not use some of the waste heat from the engine to drive a small stirling engine that in turn would drive a generator to put power back in the hybrids batteries? Even a trickle charge. I know there is no free lunch, but the weight of the sterling may be able to be offset by smaller cooling components. Use a stirling engine instead of a radiator, or pull the heat from the engine oil. Could this be a way to capture some of the wasted energy from an IC engine? Does this make any sense? ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [January 27, 2008, 9:35pm UTC](https://boards.straightdope.com/t/a-question-about-my-new-fascination-with-stirling-engines/435197/2 "2008-01-27T21:35:52Z")
[QUOTE=enipla] These engines run on a differential of temperature. As little as a few degrees. [/QUOTE] Right - but their efficiency is related to the temperature difference (specifically, to the ratio of the absolute temperatures of the hot & cold ends). So if you want useful power, the Sterling engine will need to be of reasonable size and weight (and thus cost). If you want additional output (say, for faster battery charging), in most cases you’ll do better simplay to specify a slightly larger IC engine in your hybrid. ---
**Author:** ![Mongo\_Ponton](https://avatars.discourse-cdn.com/v4/letter/m/eb9ed0/32.png) [@Mongo\_Ponton](https://boards.straightdope.com/u/Mongo_Ponton)\ **Post date:** [January 28, 2008, 4:59am UTC](https://boards.straightdope.com/t/a-question-about-my-new-fascination-with-stirling-engines/435197/3 "2008-01-28T04:59:58Z")
Well that sucks I was rooting for you enipla. ---
**Author:** ![Tuckerfan](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@Tuckerfan](https://boards.straightdope.com/u/Tuckerfan)\ **Post date:** [January 28, 2008, 5:05am UTC](https://boards.straightdope.com/t/a-question-about-my-new-fascination-with-stirling-engines/435197/4 "2008-01-28T05:05:05Z")
Stirlings also have the problem that they gradually equalize in temperature, and thus quit working. I read once where someone had built a car that ran on a stirling engine, but it wasn’t successful. ---
**Author:** ![matt](https://avatars.discourse-cdn.com/v4/letter/m/a6a055/32.png) [@matt](https://boards.straightdope.com/u/matt)\ **Post date:** [January 28, 2008, 11:01am UTC](https://boards.straightdope.com/t/a-question-about-my-new-fascination-with-stirling-engines/435197/5 "2008-01-28T11:01:55Z")
[QUOTE=Tuckerfan] Stirlings also have the problem that they gradually equalize in temperature, and thus quit working. I read once where someone had built a car that ran on a stirling engine, but it wasn’t successful. [/QUOTE] Like all heat engines, the stirling engine transfers heat from its “hot reservoir” (burning fuel) to its “cold reservoir” (the outside world.) If it’s equalising in temperature, that’s because it hasn’t got a big enough radiator, not an intrinsic problem of the engine itself. Trouble is, on a vehicle you may have to turn the entire skin of the thing into a cooling radiator to use a stirling engine of halfway respectable power. An article [here](http://www.nap.edu/openbook.php?isbn=0309074487&page=151) (scroll down) mentions poor specific power (power-to-weight) and “high heat rejection requirements” as problems. Regarding the OP - the maximum theoretical efficiency for a typical IC engine (a carnot cycle with the same operating temperatures) is around 60% IIRC. Real engines are down around 25% due to a less efficient cycle, heat losses to the metal of the engine, “pumping losses” etc. So there’s a fair bit of thermal energy available for use. The question is, how to extract it? most of the energy isn’t lost to the metal of the engine, but is sent out through the exhaust manifold. When the exhaust gases leave the engine they are still hot and have some pressure left in them, that’s why you can run a turbo off them. Exhaust manifold temperature is 430-540 deg C (800-1000 deg. F), a good hot temperature for a a stirling engine. Ways to extract that energy include a turbocharger, there’s no reason why a turbo shouldn’t contribute to the engine output instead of running an intake compressor. There’s also the Atkinson cycle, where the power stroke of the engine is longer than the intake stroke, allowing the gases to expand and cool more before they exhaust. It’s used on the Prius. And in the old VW Beetle, exhaust gas heat exchangers were used to warm the car. Not too effectively, in my experience… So yes, you could put a stirling engine on the exhaust manifold of an IC engine. But you’d be looking to at least double the size of the engine for a fairly small output increase, and you’d have to find a lot of radiator space! An alternative way to think about it is to try to combine the benefits of both engines with a hybrid, and my link above states General Motors attempted to do just that. [NASA](http://www.grc.nasa.gov/WWW/tmsb/stirling/doc/ase.html) developed a 60 kW (80 hp) stirling engine for automotive use, although they don’t say in the summary how big it was and how much it weighed! If you used a smaller stirling engine, say 20hp, running of the exhaust heat of a _small_ gas engine (motorcycle engine?), say 40 hp, maybe you’d improve the power-to-weight and large radiator requirement… or maybe you’d get the worst of both worlds. ---
**Author:** ![Argent\_Towers](https://avatars.discourse-cdn.com/v4/letter/a/e8c25b/32.png) [@Argent\_Towers](https://boards.straightdope.com/u/Argent_Towers)\ **Post date:** [January 28, 2008, 11:56am UTC](https://boards.straightdope.com/t/a-question-about-my-new-fascination-with-stirling-engines/435197/6 "2008-01-28T11:56:56Z")
I’ve got nothing to contribute here, besides pointing out that the image at the top of that Wikipedia page looks a lot like a cock and balls. Maybe that’s what the infamous “Steely Dan” looked like. ---
**Author:** ![Tuckerfan](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@Tuckerfan](https://boards.straightdope.com/u/Tuckerfan)\ **Post date:** [January 28, 2008, 12:25pm UTC](https://boards.straightdope.com/t/a-question-about-my-new-fascination-with-stirling-engines/435197/7 "2008-01-28T12:25:56Z")
[QUOTE=Argent Towers] I’ve got nothing to contribute here, besides pointing out that the image at the top of that Wikipedia page looks a lot like a cock and balls. Maybe that’s what the infamous “Steely Dan” looked like. [/QUOTE] Which Steely Dan? There were at least three of them. ---
**Author:** ![elbows](https://avatars.discourse-cdn.com/v4/letter/e/b3f665/32.png) [@elbows](https://boards.straightdope.com/u/elbows)\ **Post date:** [January 28, 2008, 2:48pm UTC](https://boards.straightdope.com/t/a-question-about-my-new-fascination-with-stirling-engines/435197/8 "2008-01-28T14:48:56Z")
I was wondering something along the same line. I thought a great application would be to make a scooter where the heat of your hands on the handlebar grips contributes to building a charge or driving the bike maybe. ---
**Author:** ![enipla](https://avatars.discourse-cdn.com/v4/letter/e/54ee81/32.png) [@enipla](https://boards.straightdope.com/u/enipla)\ **Post date:** [January 28, 2008, 3:09pm UTC](https://boards.straightdope.com/t/a-question-about-my-new-fascination-with-stirling-engines/435197/9 "2008-01-28T15:09:48Z")
Thanks everyone. So it _may_ not be an entirely stupid idea. I was thinking of something of about 5 hp. I would think that would be enough to charge the batteries. But, then it may not be worth it. The more battery life you have, the less you would have to use the IC engine. But then, the less heat you would produce to run the stirling. I didn’t think about the possible cooling problems of the stirling. But since it would be cooling the engine, I would think that the engines cooling components could be down sized a little bit. All that wasted heat……. Seems there should be a way to do something with it. ---
**Author:** ![jjimm](https://avatars.discourse-cdn.com/v4/letter/j/ba8739/32.png) [@jjimm](https://boards.straightdope.com/u/jjimm)\ **Post date:** [January 28, 2008, 3:11pm UTC](https://boards.straightdope.com/t/a-question-about-my-new-fascination-with-stirling-engines/435197/10 "2008-01-28T15:11:36Z")
[QUOTE=Argent Towers] I’ve got nothing to contribute here, besides pointing out that the image at the top of that Wikipedia page looks a lot like a cock and balls. Maybe that’s what the infamous “Steely Dan” looked like. [/QUOTE] That would be a perfect application of such an engine - the “business end” would get nice and warm while the other part would be at room temperature. Eco-dildos! We’re going to be rich, RICH I tell you! ---
**Author:** ![Ins\_Outs\_What-have-yous](https://avatars.discourse-cdn.com/v4/letter/i/8797f3/32.png) [@Ins\_Outs\_What-have-yous](https://boards.straightdope.com/u/Ins_Outs_What-have-yous)\ **Post date:** [January 28, 2008, 3:12pm UTC](https://boards.straightdope.com/t/a-question-about-my-new-fascination-with-stirling-engines/435197/11 "2008-01-28T15:12:28Z")
[QUOTE=TuckerFan] Which Steely Dan? [/QUOTE] **Argent Towers** was probably referring to the ‘steely dan’ dildo in William S. Burrough’s novel _Naked Lunch_ which was the source of inspiration for the name of Fagan and Becker’s music group. Back to the OP topic, I built a Stirling engine from a model kit during my freshman year studying engineering (2001). The warmth of a hand would power the engine a little bit but the axle turned faster when I used a cigarette lighter and an ice cube. Stirling engines will likely never be useful for automotive purposes, but they possibly could provide clean, efficient geothermal generation of electricity in the future. The heat source would be underground magma and the heat sink would be cool ocean water. I could see Stirling engine power plants being a boon to future energy needs after years of deep drilling advances and infrastructure changes. The geothermal electricity could then power electric vehicles (EVs). ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [January 28, 2008, 9:52pm UTC](https://boards.straightdope.com/t/a-question-about-my-new-fascination-with-stirling-engines/435197/12 "2008-01-28T21:52:10Z")
[QUOTE=Ins&Outs&What-have-yous] … they possibly could provide clean, efficient geothermal generation of electricity in the future. The heat source would be underground magma and the heat sink would be cool ocean water. [/QUOTE] Would Stirling engines be superior to steam systems? Various Googling produces links (including this [Wiki article](http://en.wikipedia.org/wiki/Geothermal_power)) that suggest steam is used for most medium- and large-scale geothermal power generation today. ---
**Author:** ![Gangster\_Octopus](https://avatars.discourse-cdn.com/v4/letter/g/a8b319/32.png) [@Gangster\_Octopus](https://boards.straightdope.com/u/Gangster_Octopus)\ **Post date:** [January 28, 2008, 11:46pm UTC](https://boards.straightdope.com/t/a-question-about-my-new-fascination-with-stirling-engines/435197/13 "2008-01-28T23:46:43Z")
[QUOTE=Xema] Would Stirling engines be superior to steam systems? Various Googling produces links (including this [Wiki article](http://en.wikipedia.org/wiki/Geothermal_power)) that suggest steam is used for most medium- and large-scale geothermal power generation today. [/QUOTE] There really is no reason to use a Stirling enginge for geothermal as geothermal is already a clean resource when it is run on steam. However, Stirling solar generators have been developed and ther are plans to build large central station arrays of them, although those projects are finding it difficult ot get the financing together. ---
**Author:** ![Ins\_Outs\_What-have-yous](https://avatars.discourse-cdn.com/v4/letter/i/8797f3/32.png) [@Ins\_Outs\_What-have-yous](https://boards.straightdope.com/u/Ins_Outs_What-have-yous)\ **Post date:** [January 29, 2008, 12:03am UTC](https://boards.straightdope.com/t/a-question-about-my-new-fascination-with-stirling-engines/435197/14 "2008-01-29T00:03:41Z")
[QUOTE=Xema] Would Stirling engines be superior to steam systems? [/QUOTE] Stirling engines have greater efficiency potential (i.e. greater output of energy given the same amount of heat input) than steam engines. However, it could be a decade or three, if ever, before Stirling power stations become a reality due to current deep drilling technology limits and the associated need for research and development. ---
**Author:** ![ralph124c](https://avatars.discourse-cdn.com/v4/letter/r/8797f3/32.png) [@ralph124c](https://boards.straightdope.com/u/ralph124c)\ **Post date:** [January 29, 2008, 1:57am UTC](https://boards.straightdope.com/t/a-question-about-my-new-fascination-with-stirling-engines/435197/15 "2008-01-29T01:57:14Z")
Back in the early 1960’s two big firms (NV PHILIPS, the Netherlands), and the FORD MOTOR Co. (USA) jointly worked ona Sirling engine. FORD wanted it to power cars, PHILIPS wanted it for rural power systems. After 9 years and many milions, they came up with something that was ALMOST as good as a 35 HP IC engine. Too expensive, too complex, and slow revving, the engine was not a success. ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [January 29, 2008, 2:43am UTC](https://boards.straightdope.com/t/a-question-about-my-new-fascination-with-stirling-engines/435197/16 "2008-01-29T02:43:52Z")
[QUOTE=Ins&Outs&What-have-yous] it could be a decade or three, if ever, before Stirling power stations become a reality due to current deep drilling technology limits and the associated need for research and development. [/QUOTE] Why would a geothermal power station using sterling engines need different drilling technology from one using steam (of which numerous examples exist today)? ---
**Author:** ![Ins\_Outs\_What-have-yous](https://avatars.discourse-cdn.com/v4/letter/i/8797f3/32.png) [@Ins\_Outs\_What-have-yous](https://boards.straightdope.com/u/Ins_Outs_What-have-yous)\ **Post date:** [January 29, 2008, 4:36am UTC](https://boards.straightdope.com/t/a-question-about-my-new-fascination-with-stirling-engines/435197/17 "2008-01-29T04:36:40Z")
[QUOTE=Xema] Why would a geothermal power station using sterling engines need different drilling technology from one using steam (of which numerous examples exist today)? [/QUOTE] Stirling engines wouldn’t need different drilling tech as far as I know, and I didn’t intent to imply that. Greater drilling technology would make geothermal energy (steam or otherwise) viable for more regions on Earth, not just those with hot rocks within a couple miles below the surface, if we could cost effectively drill deeper. Also, ground instability is sometimes a risk when pumping water at high pressure into deep bore holes to create the necessary steam for a steam power station. This _may_ not be a problem (although I’m being hypothetical here) with a Stirling engine as it _may_ not require the employment of high pressure water and steam in a geothermal application. ---
**Author:** ![enipla](https://avatars.discourse-cdn.com/v4/letter/e/54ee81/32.png) [@enipla](https://boards.straightdope.com/u/enipla)\ **Post date:** [February 23, 2008, 2:22pm UTC](https://boards.straightdope.com/t/a-question-about-my-new-fascination-with-stirling-engines/435197/18 "2008-02-23T14:22:14Z")
Maybe my idea isn’t so far off after all. [Honda](http://www.autoblog.com/tag/honda%20heat%20hybrid/) Is looking at a small steam engine to recapture the heat energy from the engine to help charge the batteries on a hybrid. > [@](#): > > Hybrid vehicles have always offered more benefits to the zip-around-town Domino’s pizza delivery boy than the long-distance highway commuter. In fact, without regernative braking at work, a hybrid vehicle at highway speeds exhibits very few efficiency advantages over a frugal Mini Cooper > [@](#): > > Addressing one of the problems, Honda is now touting a “heat-harnessing hybrid”, claiming it can recapture energy that most conventional hybrids lose during high speed driving. Greatly simplified, the innovative approach uses exhaust heat to convert water to steam. The steam turns an electric generator that then charges the vehicle’s battery pack. I thought that a stirling engine would do the trick. I suppose I am wrong. Thermodynamics being what they are, I guess that the cool side of a stirling would not stay cool long enough (thought perhaps with highway speeds it could be air cooled). ---
**Author:** ![Tuckerfan](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@Tuckerfan](https://boards.straightdope.com/u/Tuckerfan)\ **Post date:** [February 24, 2008, 12:36am UTC](https://boards.straightdope.com/t/a-question-about-my-new-fascination-with-stirling-engines/435197/19 "2008-02-24T00:36:33Z")
[QUOTE=Ins&Outs&What-have-yous] **Argent Towers** was probably referring to the ‘steely dan’ dildo in William S. Burrough’s novel _Naked Lunch_ which was the source of inspiration for the name of Fagan and Becker’s music group. [/QUOTE] Missed this the first time around. Yes, I know that the reference is to Burrough’s book, which is why I said that there was at least three of them. The one most discussed in the book is referred to as “Steely Dan number three” with one of the previous incarnations having been broken by a dyke who was over excited. I can’t believe that I forgot to link to [BMWs steam hybrid which predates Honda’s announcement by a few years.](http://www.gizmag.com/go/4936/') > [@](#): > > A large percentage of the energy released when petroleum is burned disappears out the exhaust system as heat. This has always been the case but the amount of energy released looks set to be cut by more than 80% thanks to a new system devised by BMW. BMW’s announcement of the new technology is somewhat of a technological bombshell as it adds yet another form of hybrid automobile – a turbosteamer. The concept uses energy from the exhaust gasses of the traditional Internal Combustion Engine (ICE) to power a steam engine which also contributes power to the automobile – an overall 15 per cent improvement for the combined drive system. Even bigger news is that the drive has been designed so that it can be installed in existing model series – meaning that every model in the BMW range could become 15% more efficient overnight if the company chose to make the reduced consumption accessible to as many people as possible. ---
**Author:** ![enipla](https://avatars.discourse-cdn.com/v4/letter/e/54ee81/32.png) [@enipla](https://boards.straightdope.com/u/enipla)\ **Post date:** [February 24, 2008, 1:43am UTC](https://boards.straightdope.com/t/a-question-about-my-new-fascination-with-stirling-engines/435197/20 "2008-02-24T01:43:23Z")
That link broke for me **Tuckerfan** , though this one seems to get to it. > **[BMW unveils the turbosteamer concept](https://newatlas.com/go/4936/)** > > December 14, 2005 A large percentage of the energy released when petroleum is burned disappears out the exhaust system as heat. This has always been the case but the amount of energy released looks set to be cut by more than 80% thanks to a new... The Beamer seams to be a IC engine and steam. Directly applying tractable power to the wheels instead of storing it. IC engines and electric, the ‘common’ hybrid as we know it seems to work pretty well. The suggestion that I make, and Honda seems to be looking at, is a system that would use engine heat to charge batteries on a long trip. Or at all times. Put that waste heat to work. [Next page](https://boards.straightdope.com/t/a-question-about-my-new-fascination-with-stirling-engines/435197.md?page=2)