The Great Lakes Zephyr - Wind Energy & Hydrogen Journal

Re: Where is the fledgling hybrid aftermarket?
 
My current understanding is that hybrids use an electric motor at each drive wheel. If that understanding is correct, then each motor is in fact a separate "drivetrain" as it actually transmits the power to the wheels driving the vehicle. From that perspective, the final drive train input of a  hybrid is electrical energy. That renders the generator and it's mechanical inputs separate from the "drive train" as I would tend to think of it.
 
Considering that currently a generator is driven by an internal combustion engine, (Hopefully bio-diesel in the near future) that means that there will be considerable amounts of waste heat produced and dumped into the ambient air around the ICE. To me it would make sense to attempt the recovery of waste heat as long as ICE technology is the primary power source and thereby reduce the size and weight of the ICE, and lessening the amount of fuel it needs to burn for the same final power output at each driven wheel. Granted you will add weight by adding the stirling cycle engine so likely it won't reduce overall vehicle weight, but it should easily increase overall efficiency. Heat could be recovered from both the ICE engine block and it's exhaust gasses after any catalytic converter system.
 
I would think that the ICE transmission is geared in a manner that optimizes generator rpm for peak electrical power output.
 
Dan

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Message: 1 Date: Sun, 18 Jul 2004 07:51:51 -0700 From:
 
John Grant grantjoh@pacbell.net
Subject: Re: Where is the fledgling hybrid aftermarket?
 
"Dan Stafford wrote:
The other question is, why aren't stirling cycle engines being tied in with combustible fuel engines to recover waste heat and further increase hybrid efficiency? Once you start using electrical power as your final drive train input, it seems very logical to me to increase overall efficiency and / or available power by tapping the heat energy normally shed to the atmosphere."
 
The hybrids I know of do not use electrical power as your final drive train input. The IC engine drives through a special type of transmission.
 
John Grant
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Dan wrote:
 
Ok, I'm hearing that Stirling engines are too expensive - no surprise as there isn't much in the way of mass production currently. That's also mentioned in the first site below, BTW.
 
I'm also hearing that Stirling engines are inefficient. A simple google search on "stirling engine efficiency" came up with a number of sites stating differently. Perhaps the Stirling demo you saw was not optimized for eficiency but just to show how the engine cycle works?
 
Here are some of the things I found:

http://www.stirlingengine.com/faq/one?scope=public&faq_id=1#2
 
Q: Are Stirling engines really the most efficient engines possible?

A: In the mid 1800's a very bright Frenchman named Sadi Carnot figured out the maximum efficiency possible with any heat engine. It is a formula like this (Temperature of the hot side - Temperature of the cold side)/Temp of hot side x 100 equals the max theoretical efficiency. Of course the temperatures must be measured in degrees Kelvin or Rankine. Stirling engines (with perfect regeneration) match this cycle. Real Stirling engines can reach 50 percent of the maximum theoretical value. That is an incredibly high percentage!

Q: If Stirling engines are so efficient, why don't I have one in my car?

A: The best answer for that is to pick the MM-1 engine up after it gets up to speed. Notice that it keeps running for a minute or so. While it's very easy to build a Stirling engine that will stop instantly, there is not one thing in the world anyone can do to make one start instantly. When I get in my car I want it to start immediately (if not sooner) and be able to burn rubber off the tires as I leave the parking lot! Stirling engines can't do that. In spite of these limitations, Ford, GM, and American Motors Corp. spent millions of dollars developing Stirling engines for cars, back in the 1970's. Ford even built a Stirling that could drive away from the curb (with relatively low power) twenty seconds after you turned the start key! Many prototypes were built and tested. Then oil prices came down in the 1980's, and people started to buy bigger cars. Suddenly there was no compelling reason to build an engine that was substantially more efficient than internal combustion engines, but wouldn't start instantly. Consider an experimental version of the 1979 AMC Spirit. It was equipped with an experimental Stirling engine powerplant called the "P-40". The Spirit was capable of burning gasoline, diesel, or gasohol. The P-40 Stirling engine promised less pollution, 30% better mileage, and the same level of performance as the car's standard internal combustion engine. [From "An Introduction to Stirling Engines"] The French Research Sub Saga is Stirling engine powered. Stirling engines also work exceptionally well as auxiliary power generators/heaters on yachts (See the Whispergen at http://www.victronenergy.com/Pages2/Products/Products.htm ), where their silence is valued and good cooling water is available. They would also work very well in airplanes where the air gets colder as the plane climbs to altitude. There is no aircraft power plant (jets included) that gets any improvement in any operating conditions from climbing. Stirling engines won't lose as much power as they climb as do either piston engines or jets. Also wouldn't you like to have silent airplanes with very efficient engines that also have exceedingly low vibration levels?
 
http://www.victronenergy.com/Pages2/Products/Products.htm
 
Usable heatThe exhaust gasses of the WhisperGen are not contaminated with oil residues and are free from soot,because of a very advanced burner system. This makes it possible to recover the waste heat with arelatively simple heat exchanger (included in the WhisperGen). As a result, the efficiency of theWhisperGen as a boiler is around 95 % and the exhaust is cooled down to 80°C.
 
http://www.bekkoame.ne.jp/~khirata/academic/kiriki/begin/general.html  
High theoretical thermal efficiencyThe thermal efficiency of Stirling cycle that is used for Stirling engine is equal to that of Carnot cycle which is theoretical higiest efficiency. Expression of Carnot efficiency is follows.

1-Tc/Th

Where
Th : Higher temperature in the cycle
Tc : Lower temperature in the cycle

This means as to be large for a temperature difference, theoretical heat efficiency are higher. Among Stirling engines developed, the engine to achieve a thermal efficiency 40 % exists.
 
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It looks like the arguments against  Stirling engines stand mostly due to their general lack of developement and mass production, not inherent problems with the concept. Given the developement reach of large auto manufacturers today, it should very well be possible for them to implement fairly efficient waste heat capture while initiating reduced costs through mass production of Stirling engines. Personally I'd like to see a biodiesel / Stirling combo powered hybrid developed. I'd bet it could be done in a way that makes it much more possible to operate the US vehicle fleet with much lower emissions on mostly domestically produced power. Diesel locomotives are actually diesel-electric hybrids. There must be a reason for that. Interestingly enough one of the sites I saw in my search above indicated that Dean Kamen is likely devoloping a shoebox sized version of a Stirling engine to power Segways in the future. http://www.segwaychat.com/forum/topic.asp?TOPIC_ID=434
 
Dan