and now, back to the theorists.
lots of people call many variations Stirling engines. if a purist things the whole world has gone mad and they are all wrong and have strayed from the absolute pure and true, well, who knows. but the notions of a sealed fluid machine that works by having a hot end, a cold end, and a cycle of expansion and compression seems to unite people to at least have a common term for their favorite underdog technology.
Rev Stirling devised the regenerator, something that soaks up the heat when it is coming from the hot end to the cold side, and gives it back to the cold stuff on its way back to the hot side, for the purpose of saving fuel. Modern people have fancy names for why and efficiency numbers. Stirling was trying to save fuel, for reasons never known for sure.
Another way to improve the Stirling action is to either make the hot end hotter and the cold end colder. I see many power Stirling engine designs that seem to ignore the cold side. The st-5 is a notorious example. A few cooling fins exposed to the air doesn't seem to me to really be a strong effort. Also, burning husk in a piece of junk wood box really doesn't seem a serious attempt to fire up the hot end. If the ST-5 needs improvement, heating the hot and cooling the cold seems a lot more bang for the buck than reinventing the regenerator.
I was chatting with my teenage son about this stuff last night. We have a coffee cup Stirling engine. As I was trying to explain theory of regenerator, he wanted to show me something. He put the thing on an ice pack, then took the hair dryer and heated the top side. The thing went so fast, it flew apart, with the propeller flying across the kitchen. Everybody broke out laughing, except him, who thought he was in trouble. Naw, he wasn't, I laughed too, and we put the thing back together pretty easy. The point was made quite clear to me.
Lets say I have some Stirling engine and I want to use it for power production, for me, at my home, given my unique conditions. There are things that I can do to increase the effectiveness, hopefully to make it practical. The purist would say these things are very complicated and take from the efficiency. But that is really really true, or doesn't have to be.
Like, Rev Stirling, I want to get the most from my fuel, which we will say is firewood in my case. There are things I can do to make the hotter end hotter. Let's say I'm using a wood stove to burn the wood. If I put my wood stove inside a kiln, with the hot end of the Stirling coming right into the kiln and into the stove, this thing will heat up much more just from physical construction.
Now, let's say I take a separate little Stirling I buy, that runs off the stove heat to spin a fan, and use it to force air into the stove, turning it into a wood furnace. I have plenty of heat to spare, and I don't have to "rob" my main Stirling to do things to help it. This is also an example of feedback I was also trying to explain to my son. As the little Stirling fan force blows air into the furnace, the furnace gets even hotter, making the little Stirling spin even faster, making the furnace even hotter, up to the limit of the wood capacity or the stove goes meltdown on me.
Here is the link to the little stove fan for my theoretical example:
Also, we know at home, in my real wood furnace, that we don't want truly seasoned wood, and some wood burns hotter than others. If I use harder wood and let it dry completely and put that in my furnace, the heat becomes too much too easily. So, I could make my theoretical Stirling furnace use the hottest driest wood fuel. The would increase heat quite a bit.
Now, on the cold side, I buy a second little stove-top Stirling fan, and use it to slowly pump the very very cold water from the well under the house up to the bathtub-from-the-junkyard I am using for my water cooling tank on the cold end of the Stirling, instead of air cooled fins. The tub is allowed to drain out the drain hole, and back into the ground through the septic system, which will never affect the temperature in the well.
As you can see, what I am doing is "cheating" on the Stirling cycle, and trying to turbo charge the process.
None of this is my "big idea", that has to do with a regenerator. But, I think you can see where this is going.
A purist would cry foul, and throw me out of the Stirling engine genius contest.
But, if people in real need in parts of the world where unconventional energy sources would save the day, people who have real expertise in such machines should encourage them to do anything practical and some things even silly, if it would help them to help themselves. Solutions can be unique to situations to overcome the perceived doom-to-failure belief, when a little creative Yankee inspiration might just push the heat engine theory over the mark.