I am new to the Stirling Community and I have been reading a lot
about Stirling Engines lately. Everywhere I have read so far, people
say that the main problem with Stirling Engines in cars is the
pickup or in other words, how long it takes for it to warm up. Can
this problem be solved by using a hybrid format where the energy
would be stored in a battery and that would be used to run a car
until a Stirling heated up? And then the power that the engine
produced could be used to constantly recharge the battery. That
would also solve the accleration/decelaration problem with Stirling
Engines. And if this is possible, I would like to know whether or
not it has been implemented and if not why? Any feedback would be
appreciated. Thanks.
Pickup problem with Stirling Engines in cars.
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stan.hornbaker
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Stirling Engines in Autos, Why Not?
Stirling engines are normally constant speed machines. They are difficult to regulate or to set to a specific speed. Fuel requirements/HP also are a problem in an automotive application.
You can read more on this site via the "Site Map" and at "How Stuff Works," under Stirling Engines.
You can read more on this site via the "Site Map" and at "How Stuff Works," under Stirling Engines.
Response to Pickup problem with Stirling Engines in cars.
The correct answer is, "Yes, a hybrid model could work." The caveat is that the vehicle needs to be of a type known as a "series hybrid" where all motive power is produced by the electrical engine. The only purpose of the Stirling engine would be to charge the batteries and/or provide electricity directly to the motors.
This page explains the Series Hybrid concept in detail. This scheme has been used in the Coaster Hybrid Bus and Ford Escort Hybrid Prototype.
Generally hybrids are of a "parallel hybrid" type for reasons of efficiency. You see, everytime you convert energy from one form to another, you lose some of the energy in the conversion. In the case of a series hybrid, you need to first convert the motion of the engine to electricity. If you use an alternator instead of a dynamo, then you need to convert the AC to DC for storage in the battery. The electricity is then converted into potential energy inside the chemicals of the battery. Once the energy is released as electricity, it then must be converted back to mechanical motion by the electrical motors.
As you probably figured out, we're losing a lot of energy in the system just described. For that reason, most hybrid cars run in "parallel" mode so that the mechanical motion of the engine can be applied directly to the motion of the car. Unfortunately, there are so few times when the power output of your Stirling engine would match up with the power requirements of your driving, that's it's impractical to place the Stirling in a parallel configuration.
With that in mind, it's still important to remember that Stirling engines can be quite a bit more efficient than internal combustion engines. As such, it's quite possible that the gains/losses would balance out to some degree. Which means that it is feasible with modern technology to build a car that can run off of gasoline, diesel, ethonol, biomass, heating oil, or some combination there of. More exotic fuels such as hydrogen and propane would work in the engine, but the car would require a different fuel system to support them.
The chief reason for not implementing a Stirling hybrid at this point (especially with gas prices skyrocketing!) seems to be the cost of manufacturing the Stirlings themselves. For some reason, they seem to run $1,200/kW and up. Which means that a 55kW engine would cost $66,000!
What I don't understand is *why* the engines are so expensive. They're not *that* different from existing engines, and in many ways are actually much simpler. My only guess is that the high prices have to do with the low quantities produced combined with the inexperience the industry has in making them. Any engineer may be able to create a Stirling engine, but creating an efficient, high performce Stirling engine is a whole other ballgame. Since the industry has far more experience with gasoline engines, that's where the efficiency remains.
This page explains the Series Hybrid concept in detail. This scheme has been used in the Coaster Hybrid Bus and Ford Escort Hybrid Prototype.
Generally hybrids are of a "parallel hybrid" type for reasons of efficiency. You see, everytime you convert energy from one form to another, you lose some of the energy in the conversion. In the case of a series hybrid, you need to first convert the motion of the engine to electricity. If you use an alternator instead of a dynamo, then you need to convert the AC to DC for storage in the battery. The electricity is then converted into potential energy inside the chemicals of the battery. Once the energy is released as electricity, it then must be converted back to mechanical motion by the electrical motors.
As you probably figured out, we're losing a lot of energy in the system just described. For that reason, most hybrid cars run in "parallel" mode so that the mechanical motion of the engine can be applied directly to the motion of the car. Unfortunately, there are so few times when the power output of your Stirling engine would match up with the power requirements of your driving, that's it's impractical to place the Stirling in a parallel configuration.
With that in mind, it's still important to remember that Stirling engines can be quite a bit more efficient than internal combustion engines. As such, it's quite possible that the gains/losses would balance out to some degree. Which means that it is feasible with modern technology to build a car that can run off of gasoline, diesel, ethonol, biomass, heating oil, or some combination there of. More exotic fuels such as hydrogen and propane would work in the engine, but the car would require a different fuel system to support them.
The chief reason for not implementing a Stirling hybrid at this point (especially with gas prices skyrocketing!) seems to be the cost of manufacturing the Stirlings themselves. For some reason, they seem to run $1,200/kW and up. Which means that a 55kW engine would cost $66,000!
What I don't understand is *why* the engines are so expensive. They're not *that* different from existing engines, and in many ways are actually much simpler. My only guess is that the high prices have to do with the low quantities produced combined with the inexperience the industry has in making them. Any engineer may be able to create a Stirling engine, but creating an efficient, high performce Stirling engine is a whole other ballgame. Since the industry has far more experience with gasoline engines, that's where the efficiency remains.
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stan.hornbaker
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Response to Pickup problem with Stirling Engines in cars.
The Stirling encine is an external combustion engine requiring that a large amount of heat at a high temperature be introduced into the engine where a small percentage, typically <30% is converted to useful work/energy and the balance rejected to the heat sink.
A great deal of R&D effort has been expended on Stirling engine designs for various applications. To date only a few niche market applications have been marketed at prices to high for widespread use. CHP and submarine applications are the current principle uses of Stirling engines. Do not look for a hybrid automobile incorporating a Stirling engine in the near term.
A great deal of R&D effort has been expended on Stirling engine designs for various applications. To date only a few niche market applications have been marketed at prices to high for widespread use. CHP and submarine applications are the current principle uses of Stirling engines. Do not look for a hybrid automobile incorporating a Stirling engine in the near term.
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scottthomas
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Response to Pickup problem with Stirling Engines in cars.
It should also be noted that a typical ICE is only 20% efficient, so efficiency is not the reason to rule out a Stirling for a particular application.
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stan.hornbaker
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Response to Pickup problem with Stirling Engines in cars.
Scott: As noted elsewhere in these forums, it is not so much a matter of efficiency as it is of energy movement through the engine.
An ICE takes in a charge of high energy fuel which is burned/exploded to drive the engine. OTOH a Stirling engine is filled with air or another gaseous medium which must be heated to cause expansion and drive the piston. With the exception of sealed crankcase machines the pressure with in a Stirling is near atmospheric at all times, else it can not run! The pressure differential across the piston varies from positive to negative.
An ICE takes in a charge of high energy fuel which is burned/exploded to drive the engine. OTOH a Stirling engine is filled with air or another gaseous medium which must be heated to cause expansion and drive the piston. With the exception of sealed crankcase machines the pressure with in a Stirling is near atmospheric at all times, else it can not run! The pressure differential across the piston varies from positive to negative.
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cyril.bouchayer
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Response to Pickup problem with Stirling Engines in cars.
Hi,
I read about 1200 $ / KW !!!!!! Do you have an idea of the price which should be reached to begin to have competitive external combustion engine ?????
Cyril Bouchayer
I read about 1200 $ / KW !!!!!! Do you have an idea of the price which should be reached to begin to have competitive external combustion engine ?????
Cyril Bouchayer
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stan.hornbaker
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Response to Pickup problem with Stirling Engines in cars.
Aside from the (pickup) warmup time the Stirling is essentially a constant speed machine. It is not readily adaptable to wide range variable speed operation as in an automotive application.
Automobile engine probably cost on the order of $750 to $2000 each depending on volume of manufacture and HP.
Automobile engine probably cost on the order of $750 to $2000 each depending on volume of manufacture and HP.
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fielding.isaacs
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- Joined: Thu Jun 08, 2006 9:28 pm
- First Name: Fielding
- Last Name: Isaacs
Response to Pickup problem with Stirling Engines in cars.
Here's a potentially crazy idea
since the Stirling engine is a constant speed machine, if one were so crazy about putting it into a car / variable speed application, why not develop a sort of inverse CVT transmission. (we seem to be getting close to developing CVT's for widespread automotive use, I know either the early toyota prius or honda whatever-it-was hybrid used one) use the Stirling engine to drive a hydraulic pump as well as the main drive gear of the transmission. Then (and this is the trickiest part here I suspect) the main transmission gear/belt drive wheel for the transmission is designed such that the hydraulic fluid flows through the gear/belt changing its radius depending on the pressure/flow of the hydraulic fluid, thus changing one of the radii of the gears in the transmission, thus changing the overall speed of the driveshaft. then all you need to do is make the throttle control the flow-rate of the hydraulic fluid into the drive gear and voila...controllable speed on a Stirling engine.
since the Stirling engine is a constant speed machine, if one were so crazy about putting it into a car / variable speed application, why not develop a sort of inverse CVT transmission. (we seem to be getting close to developing CVT's for widespread automotive use, I know either the early toyota prius or honda whatever-it-was hybrid used one) use the Stirling engine to drive a hydraulic pump as well as the main drive gear of the transmission. Then (and this is the trickiest part here I suspect) the main transmission gear/belt drive wheel for the transmission is designed such that the hydraulic fluid flows through the gear/belt changing its radius depending on the pressure/flow of the hydraulic fluid, thus changing one of the radii of the gears in the transmission, thus changing the overall speed of the driveshaft. then all you need to do is make the throttle control the flow-rate of the hydraulic fluid into the drive gear and voila...controllable speed on a Stirling engine.
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stan.hornbaker
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Response to Pickup problem with Stirling Engines in cars.
A CVT for automotive use is normally a planetary transmission to eliminate slippage etc. associated with belts and cones or rolling contact metallic components. I see no point in the employment of a "reverse" CVT.
The fuel consumption for a given output power is also higher for a Stirling than that of an equivalent ICE. Hence the emphasis for waste fuel or biomass applications.
The fuel consumption for a given output power is also higher for a Stirling than that of an equivalent ICE. Hence the emphasis for waste fuel or biomass applications.