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I am a University student and recently learned a bit about Stirling
engines. My professor mentioned using Stirling engines in cars. This
would be a great idea. Low power output, but a lot less pollution. My
question is the following: Can a Stirling engine be made to vary in
velocity and power output by simply pressing on a pedal?

I asked my professor and he was unable to answer. I figured maybe
someone here may know a little more.

Stirling engines can be built that will vary their power output just as quickly as a car's engine but they tend to become complex when designed for that goal. You probably have already read the FAQ on this subject so let me elaborate.

NASA and Ford (among others) built Stirling engines for cars back in the 1970's. To get the good "driveability" that people are used to while keeping the engine efficient, they had to add very complex methods for pumping helium though the engine.

It's easy to build Stirling engines that can vary their power levels both slowly and efficiently, or quickly and innefficiently, but to vary the power levels both quickly and efficiently tends to require a lot of complexity.

What seems to make the most sense to me is to run the Stirling in a hybrid configuration. Let it run at its optimal RPM and use it to run a generator. The generator would keep batteries charged. The rest of the car would be a normal electric drive train.
Low power output would not be an issue, as the motor(s) would pull as much power as needed from the batteries, not the Stirling directly.
You'd get a lightweight car with great milage.

Mick you are absolutely right that a hybrid is the only practical use of a Stirling engine in cars.

On March 20, 2002 I delivered one of our KY-2000 Stirling engines to the Mechanical Engineering department at San Diego State University. While I was there I had the opportunity to see their hybrid diesel/electric car. It has a 60 hp diesel engine and a 200 hp electric motor. The extra power (above 60 hp) for the electric motor is of course supplied by the batteries when needed.

Now imagine that you were the lead engineer on a project to design a hybrid car for Honda, Toyota, or San Diego State. Would you choose to use a fourth generation Stirling or perhaps a 100'th generation gasoline or diesel engine?

A Stirling could drive the pump of an hydrostatic transmission. There are noisy lawn tractors with IC engines using hydrostatic transmissions as well as many forms of heavy construction vehicles. There is probably a size on the market perfect for your idea.

Tom Ward

I'd like to very respectfully disagree with Tom. Markets that are being well served by existing cheap technology are not likely to change to Stirling power even if they could.

On the other hand, markets that demand something that a Stirling engine can do well and other engines can't do very well or can't do at all are great target markets for Stirling engines. Remote power, users who demand silence, multi-fuel users, these are all good target markets for Stirling engine introduction.

Sounds like a concept car I had in the back of my mind since I've started to study Ringbom. I use AC motors in my line of work. The Industry has off the self drives that can take DC and operate a 3 phase AC motor. The drives can be speed or torque controlled. I believe four 10hp motors would be enough for a commuter car. Just think; no transmission, no oil, four wheel full time drive.

I am considering building a Stirling engine of about 10Kw for use in mini subs and ROV's. Using a hybrid Stirling/Electric solution to provide sufficient control when I get that far. Anyone seen designs of this capacity ?

You have quite ambitious plans and I hope you succeed! The French research sub Saga was said to be powered by a Stirling engine. I'm not sure but I think the engine was built by Kockums. The Kockums AIP Stirling powerplant for their full-size submarines is approximately 150 kilowatts. Unfortunately it is as large as so mini subs all by itself.

You might also want to check with Koichi Hirata (see my links page) because he is quite interested in Stirling engines for undersea vehicles.

Doctor Davison, I like your idea of a Stirling powered ROV and have been thinking of improvements you could make to your final design:
How about an extendible water input pipe that your ROV could direct into the output stream of a thermal vent? The incredibly hot water could power up/recharge your batteries using a Stirling generator in no time.
You could even leave one of these devices down there (at the sea bottom) for months, collecting data and taking pictures. It could communicate with the surface through low bandwidth sonar or a powerful blue laser.
If the Stirling was designed to operate at ambient pressure (and had a valve system to ensure such) then it could be enclosed in a small bubble of gas that would slowly be crushed by the pressure of the ocean and increase the internal working volume of gas to a level that could not be easily achieved at sea level. With such enormous internal pressure the power output would be huge!
When in ‘snorkel’ mode, that is combusting fuel using atmospheric air at the oceans surface to recharge batteries, whatever exhaust heat you have could be first funneled through a thermally insulated bed of heat-storage-medium (ball bearings?). Once submerged, water could be injected into this space to give off steam (or hot water above the boiling point of sea level hot water). The ‘waste’ heat could now be used to run the Stirling to give you that much more range even though no fuel is being combusted.
Remember too, that the rejected heat from the Stirling could also be used to heat your passengers and batteries, keeping them both comfy.

One other quick suggestion that may be more ‘pie in the sky’ than anything - If you’d like to dispense of batteries and still use a fuel like diesel or propane to power the Stirling, it could be accomplished like this:
A loop of air is pumped through a device with a gas permeable membrane and a huge surface area much like the gills of a fish (or our lungs) that allows CO2 to leave and O2 to enter. The now oxygen rich air is piped to the combustion chamber where fuel is mixed and burned. The exhaust of CO2 and water is sent back to the ‘lungs’. Water is condensed out and CO2 removed. Oxygen from the surrounding seawater forces it’s way in and the loop is continued.
This system would operate much like a living organism, where it must breathe seawater and eat food (diesel). No exhaust and no bubbles. Nice and quiet for those long giant-squid hunts.
Air would also be unlimited for passengers who’d share the lung with the engine.