Filed under: EV/Plug-in, Hybrid
Dean Kamen working on Stirling engine-assisted electric car
Stirling engine - Wikimedia commons
The internal combustion engine, as we've known it for over a century, is what's known as an open cycle device. That is, the so-called working fluid flows into and out of the engine and is constantly circulated. A closed cycle engine keeps the same working fluid contained within the device and heat is generated externally rather than from combustion inside the cylinder. The best known example of the latter is the stirling cycle engine. The advantage of the stirling cycle is that the heat source can be anything since the combustion (or non-combustion) occurs outside of the mechanism. The theoretical thermodynamic efficiency of the stirling cycle is 100 percent although creating a 100 percent efficient mechanism has proved elusive. Nonetheless, the flexibility of the stirling engine has made it a popular choice among those researching alternative powertrains.
When it comes to alternative anything, few people rank with Dean Kamen. Kamen is best known to most people as the creator of the oft-derided, but certainly innovative Segway scooter. For some time now, Kamen and his staff have been working on a extended range electric vehicle. As with most other EVs of late, energy storage comes in the form of the usual array of lithium ion batteries. The stirling engine will be used to recharge the battery pack making the car useful for more than just urban commuting. If anyone can make the stirling engine work in a car, Kamen might be the one. We'll have to wait and see.
[Source: The Telegraph]
Reader Comments (Page 1 of 3)
paulwesterberg 3:31PM (10/28/2008)
Most of the energy(75%) in gasoline is wasted by an internal combustion engine.
The prius gets great gas mileage mainly by capturing regenerative brake power and by not running the motor in town, but it still wastes 75% of its gas.
If you use a sterling engine to capture some of that wasted energy you could probably downsize the prius or volt engine and get 70-80mpg while still using gas. Probably still nowhere near as efficient as electric, but it might be cheaper and easier to fit into existing car designs.
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sunnycyclist 3:39PM (10/28/2008)
I'm just wondering why that particular picture was chosen. There are some much more informative ones on Wiki, and, not to sound like a thirteen-year-old boy, but this one looks like something out of Austin Powers.
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James 3:46PM (10/28/2008)
I second that.
Chris M 9:51PM (10/28/2008)
There are several different designs for Stirling engines. The one illustrated is a beta cycle with rhomboid drive. If you see something "Austin Powers" about it, you've got an overactive imagination.
Alpha cycle stirlings have separate displacement and power cylinders linked by a regenerator.
Beta cycle stirlings have the displacer piston and power piston in the same cylinder, often the displacer acts as a regenerator.
Gamma cycle stirlings are multi-cylinder design where the hot end of one cylinder is linked to the cold end of the next, and the same piston acts as both displacer and power piston.
nathan 3:30PM (4/30/2009)
if you don't see something austin powersish about this illustration, you have an underactive imagination.
Celso 4:22PM (10/28/2008)
Actually, a sterling engine would work great in an all electric car. Simply use the sterling engine to keep the battery bank charged.
The heat source could be taken from several places (ie. breaks, sunlight and some sort of clean(er) fuel)
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champ 5:15PM (10/28/2008)
The heat sources for a sterling engine if a vehicle are numerous. Remember, the source of heat for a sterling engine only has to be hotter than the ambient air, so almost anything can be a heat source.
- the driver & passengers, as long as its cooler than 98.6 degrees outside.
- breaks (already mentioned)
- The sun (already mentioned), could just be the sheet metal getting hot under the sun.
- friction from the moving joints in the drive train
- the tires get pretty warm
- the electric motor puts off heat
- the electronics/onboard computer
- the radio
- I'm sure there's more.
Chris M 5:54PM (10/28/2008)
Stirling engines could be well suited for series hybrid use, as they run best at a constant power constant speed output, and can use almost any fuel for heat, and under the right circumstances can achieve higher efficiency than standard IC engines.
Efficiency is affected by the temperature difference between heat in and heat out, the greater the temperature difference the more efficient it is and the higher the power output. This means using a high temperature burner for "heat in" and the largest radiator possible to cool the "heat out". It might even be worth considering using liquid nitrogen to help cool the "heat out" on the engine, if the cost was low enough and sufficient cryogenic storage was possible.
Sorry, Champ, but those heat sources you mentioned really aren't hot enough to provide useful amounts of power. It is far more efficient to use a generator for regenerative braking than to use friction brakes and try to recover some energy from the heat.
kert 5:19PM (10/28/2008)
For series hybrid, stirling would be basically the best choice from efficiency standpoint, if it can be made in small enough configuration, meaning with decent power to weight ratio.
Other alternatives would be turbines or linear combustion engines.
I would expect these options to actually appear in large trucks first, as its easier to fit something like a stirling in a truck rather than a passenger car, and savings in fuel costs would be very significant for fleet operators.
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EVan 6:17PM (10/28/2008)
The gas turbine is still the efficiency champ but automakers just haven't been able to get the design of the regenerator right.
If anything is going into a series hybrid other than a gas powered internal combustion engine anytime soon I'd put my money on these options
In order of most likely to least likely.
1. E-85 ICE
2. Natural Gas ICE
3. Hydrogen ICE
4. Fuel Cell
5. Gas Turbine
6. Free Piston Engine
7. Stirling Engine
8. Nuclear Reactor (it's bee done!)
!!D 8:04PM (10/28/2008)
@EVan: I'd add this to your list before E85 since it requires no changes to the vehicle or fueling infrastructure:
0. Biobutanol ICE
See http://sustainabledesignupdate.com/?p=1004
gorr 5:38PM (10/28/2008)
Im sorry to kill your dreams tonight but a sterling engine is just a toy. This thing is just turning and making some nice sound. It turn by a heat source but it just have the power to keep turning by himself and as soon as you plug a charge on it like an electrical generator then it stop because it don't make power.
A solar panel on the roof of the car is more useful and efficient to charge the batteries, about 1 to 2 miles a day on a sunny day where there is no hills.
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Chris M 6:07PM (10/28/2008)
Some Stirling engines are toys, made to demonstrate basic thermodynamic principals. Running on modest heat sources, the toys don't produce much power, in some cases producing barely enough power to spin a small fan.
But there are also much larger and more powerful Stirling engines that can produce several hundred horsepower, and these are used in some industrial applications and on some ships.
Stirling engines were used in a few experimental prototype cars, and it is possible to make them small enough yet powerful enough for automotive use. The big drawback was slow response to throttle input, but that isn't a problem for series hybrid use.
Snowdog 5:56PM (10/28/2008)
If anyone can get a Stirling working for automotive use it is Kamen, who has quite a bit of experience with them, and is willing to spend the time to get it working.
Using them as a range extender for a BEV is a better application than trying to get them to drive the wheels directly.
BUT there are significant hurdles. They are very expensive to build and very large/heavy for the power they produce. Not the ideal when you want to produce an efficient automobile. Double the engine efficiency but then your car weighs (and costs) twice as much.
Still I wish him luck on this project. Lets code name it "Mary Ann".
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Dick Army 6:16PM (10/28/2008)
Why does the engine look a huge penis?
!!D 7:57PM (10/28/2008)
I agree, mostly, with Snowdog. However, I don't think "range extender" is quite the right term. A ranger extender is usually applied to something that is switched on to provide power on demand; whereas a stirling engine driven generator will most likely be an always-on battery charger since it is quiet and has no exhaust.
(I'm assuming the stirling is driven by waste vehicle heat, not by a specific combustion source. We'll have to wait to see how Kamen arranges the system)
Snowdog 8:17PM (10/28/2008)
It certainly NOT going to be driven waste heat. It's going to burn fuel, likely regular unleaded gas.
Waste heat from what??? This not some toy to be driven by body heat to turn a little wheel. It will need to generate 50KW+ of energy output so it will need the equivalent in heat production, this is only attainable from burning fuel and lots of it.
It will not run all the time as it makes no sense when the batteries are full, because you want to keep spare capacity in the batteries to capture regen braking energy and you likely also want to have some range before you burn any fuel, so if your commute is short you burn no gas, just like other PHEVs.
This is strictly meant to be a more energy efficient gen-set for a PHEV like the volt. So it might in theory get 80MPG compared the the volts 40MPG when burning fuel.
!!D 12:08AM (10/29/2008)
@Snowdog: You're right, always on isn't accurate either. Maybe trickle-charge-on-demand. I assert "trickle charge" as Kamen's intended use for the Stirling engine based on point #5 in the "Powering Up" graphic in this CNN.com article
http://money.cnn.com/magazines/business2/business2_archive/2007/08/01/100138830/index.htm?section=magazines_business2
And if it is true that the stirling engine only provides a trickle charge, then I don't believe the engine needs to be anywhere near 50 KW. However, to make the car reliable (especially in cold climates) I concede waste heat would not be the energy source.
Snowdog 6:53AM (10/29/2008)
Nice find on the link.
If all it does is trickle charge, it is a completely useless novelty. As as soon as you try to go long range and you flatten the battery, you would have to pull over and wait hours for the battery to charge.
Completely pointless. Efficiency is nice, but I will take a 25% efficient ICE that actually lets me drive over 80% efficient Stirling that requires me to park it for a day to recharge.
Chris M 11:34PM (10/29/2008)
It will certainly be more than a "trickle charge", a range extender for a well designed plug-in hybrid should provide more than enough power for steady cruising. The battery shouldn't be completely "flattened" before the range extender kicks in, the vehicle needs some reserve power from the battery for rapid acceleration and the occasional hill climb.