Stirling Engine!

[mattb28]

There is one website that claims you can build an electrolyser(?) fuel cell. U can get energy by splitting the hydrogen and oxygen atoms that make up water. The parts can produce a large amount of hydrogen. Sounds good, but u must be dedicated to take that on. There have been guys who have tested stuff like this, they might power a small gas engine, but not an SUV I would think. A neat idea though. Someday, somehow, someway, the world should have a better source of fuel, that will be cheap enough for all to afford, and enough of this relying on foreign oil, and practically begging for it, which ain't a good thing.

[MrForbes]

The hydrogen booster idea is pretty interesting...it separates those who understand the laws of thermodynamics, from those who don't

Think about the energy flow. The engine is running on gasoline and air, and it has an alternator that is turned by the engine, and recharges the starting battery and also provides electrical power to run the various things on the vehicle, such as lights, ignition, etc. The alternator therefore is powering the hydrolizer, which separates the hydrogen and oxygen from the water. However, it takes more electrical energy to separate them than you can get back by burning them in the engine!

The whole thing is a scam....although it seems likely that people who put these things on their cars actually do use less fuel, for an interesting side reason. They generally are true believers, and so they fully expect the device to improve their mileage, so they (consciously or subconsciously) change their driving habits, which results in an increase in mileage. In fact, it appears that instructions included with some of the systems for sale state that you have to drive differently with the device. What a happy coincidence!

I have yet to see any published report showing valid data for specific fuel consumption of an engine equipped with one of these things. And a double blind, carefully controlled mileage analysis is unlikely to ever happen....the true believers all know it improves mileage, and the skeptics (who actually might be interested in the results of the experiment) already know it won't improve mileage, so we won't bother to do the experiment because it's a waste of time.

[Rosiebotboss]

Those wonderful guys on Mythbusters did the experiments with the H2 electrolyzer (and other high mileage apparatus) and their results were an actual decrease in mileage and a pretty big boom when they introduced straight H2 from a bottle. They had reasoned that the decrease in mileage was due to the fact that not enough H2 was being produced, so they, in typical Mythbuster fashion, "ramped up" the dose!

Great segment. They did a good job busting the high mileage myths...

[Gdeaver]

Yes, Sterling engines are amazing devices. They will be used in the future to reclaim work from waste heat. For cars, BMW is testing a 2 stage sterling engine that they added on to one of their large V8's. Should be available for general purchase in the fall in European markets. The press release I read stated that it added about 45 HP at cruise speeds. Auto engineers have done an amazing job over the years of improving the combustion efficiency and lowering the pollution of internal combustion engines. However, the internal combustion engine is thermally inefficient.

[Krystine T.]

I love Stirling engines! I've designed one out of brass and aluminum. Hopefully someday soon I will actually get around to making it. The one I’ve designed, which will run off of a small candle, won't be anything more than a conversation piece, but it is a great demonstration of how to turn heat into work. I've also learned that if you run the engine in reverse, for example, off of a small dc motor, it will actually create a hot and cold side. Because of this the engines are also used in cryogenics.

[mattb28]

Awesome input from everyone! The stirling is quite the device. I just wish someone would get to the root of the problem with fuel, and fix it. When they had the televised presidential debates a few months back, John Mccain had said if he was President, he would put out a $1,000,000 reward I think it was, to the first person who can get you, the consumer, 100 miles to the gallon. A guy has already done that. Jonathan Goodwin, but he charges a lot, so financially it doesn't make sense for most people. Biodiesel, is cheap, around $1.50 for b20 I think, not sure though, we are headed in the right direction, things are goin so slow, so many things stand in the way. I might sell my car, and just ride a bike to work, or just take the bus.

[MrForbes]

The little cars in the supermileage competition get between a few hundred and 1500 mpg. They aren't practical for transportation, though.

$1,000,000 won't buy much product development these days.

The government can help by raising mileage requirements, which forces carmakers to sell smaller, lighter cars. Fuel prices will have to get very high before folks who can easily afford $50k+ SUVs really have to worry about the cost to operate them. Depreciation is still the biggest expense!

[mattb28]

I have seen a few trucks around here with biodiesel stickers. It's still doesn't solve the problem. Biodiesel is still in a developmental stage so to speak if you ask me, it's hard to come by. Not every station has it. It might be cheaper, but slightly more work involved in getting it in your tank. As far as regular cars, not sure. Pretty much every station in Framingham is around $4.00, which too me is nuts. I hope the sierra club and the environmentalist groups are happy, a lot of people are gonna ditch their SUV's and many truck driver's will quit if this keeps up at the pumps

[Pat Major]

Interesting 15 minute video from GM in 1969, includes a Stirling powered car. http://video.google.com/videoplay?do...78756207191901.
Form your own conclusions as to how difficult this problem is to solve and how far we have come

[kramarczyk]

Originally Posted by Pat Major

Interesting 15 minute video from GM in 1969, includes a Stirling powered car. http://video.google.com/videoplay?do...78756207191901.
Form your own conclusions as to how difficult this problem is to solve and how far we have come

Fuel Cells & Hybrids & CVT's
Oh my!!!

[Why_A_Username?]

So I read the thread, and it got me thinking. I did some research into the sterling engine, and an article by how stuff works (http://auto.howstuffworks.com/stirling-engine.htm) said that they are primarily used by submarines and yachts as backup power systems. this means they are mostly used for electrical power production. The main issue with using them in the place of an internal combustion engine (ICE) is that sterlings are low speed, and react slowly to changes in the throttle.

However, and this is where my own thinking starts, there is a work around. With hybrid cars so common, the technology is here. I propose the use of a sterling as an electric generator, spinning an over-sized alternator at a near-constant rate. The alternator would charge a battery bank, which in turn could be used to power electric motors in the drive train. The system I have just described is largely similar to that used in the Nissan Leaf, the primary difference being that in the place of the ICE, we have a sterling.

This is more efficient than a standard motor for a lot of reasons, chiefly because the Stirling would not require gear shifting and large gearing changes, which are one of the least efficient parts in a modern car's drive train. Sterling engines are also innately more efficient than ICEs.

If anyone knows if a car has already been powered in this fashion could they please let me know, as I am very much curious about the implications of this idea.

[GeeTwo]

I have not done the formal math or testing on this, but I took a couple of thermodynamics courses and have thought about it a bunch over the years. I am pretty certain that if a Stirling engine could be feasibly made to work in an automobile, this engine model would see much more use in land and sea based applications. If someone with more specific experience can tune or correct my thinking, please do so!

First of all, the standard claim that the Stirling is the most efficient engine possible is based on the ideal thermodynamic model - a heat source at a constant temperature, and a heat sink at a constant (lower) temperature, driving a closed-cycle heat engine*. With such a setup, it is possible to prove that the maximum possible efficiency is equal to the ratio of the two temperatures, measured in kelvin (or an equivalent system where absolute zero has value zero), and that the Stirling engine can theoretically achieve this efficiency.

That heat sink is a problem for an automobile (or worse for an aircraft), because in the Stirling model, it has to be able to dissipate ALL of the heat generated in the heat source and maintain a relatively low temperature (perhaps 420K or 150C or 300F). When radiation and air are your media of heat transport, this means a large, probably heavy, radiator. For land and sea based systems, the earth or ocean or other body of water can be used as your heat sink, greatly reducing size and weight (and oh by the way, it isn't as big a problem in the first place) -- and yet, Stirling engines are NOT the engine of choice for power plants or ships, where this problem is mitigated or solved.

The internal combustion engine (whether Diesel or Otto or otherwise) get around this limitation by eliminating much of the heat of combustion through the exhaust of the combustion by-products. Steam locomotives and many other steam engines do similarly by exhausting reduced-temperature steam, greatly reducing the required size of the heat sink. Thermonuclear steam plants are closed-cycled to contain the radiation, but most of the heat is still usually taken away by a secondary water circulation which is either released into the environment or passed through enormous cooling towers.

The internal combustion engine further reduces the system's mass-to-power-ratio by performing the combustion "on demand" inside the fluid working chamber, greatly reducing the waste due to radiation and conduction and exhaust of the products of combustion. That is, in a steam locomotive, a significant fraction of the heat of the coal burning is sent up the stack, without generating any work. Only the heat which transfers to the water in the boiler generates steam. In a gasoline or diesel engine, the gasses produced by combustion ARE the working fluid that does the work - by doing work, they cool, and are only ejected when they have done all the useful work they can. As such, an internal combustion engine can achieve better efficiency than any Stirling engine of comparable size utilizing the same fuel.


* I believe it also covers the case in which the working fluid is taken from the heat source and eliminated into the heat sink. I expect that this use case is utilized in some geothermal plants.