I made the following introductory post at the very begining of this thread, more than ten years ago:
Tom Booth wrote: ↑Tue Feb 23, 2010 6:12 pm
I've been reading quite a bit about thermodynamics lately. Especially in regard to the fact that when a gas is "made to do work" it looses heat or gets cold.
This has been a hard concept for me to grasp, but apparently, when a gas does work of any kind, the heat energy in the gas is converted into "work" or the kinetic energy - such as moving a piston.
Now, formerly I had been under the impression that a Stirling engine functions by means of a temperature differential applied to it. One end of the displacer chamber is heated and the other end cooled - the air travels back and forth from one end of the chamber to the other and picks up or looses heat in that way...
But I'm becoming aware that there is also apparently something a little more subtle going on, that is, when the air in the chamber heats up and expands and then
does work against the piston - the heat does not only travel to the "heat sink" at the cold end of the chamber but some of the heat is actually converted into work. In other words, what cools the hot expanding air back down is not so much, or not only coming into contact with the cold end of the chamber but heat is also lost on account of the gas being made to do work against the piston.
What I'm wondering is just how much heat is actually being absorbed in this way i.e converted into work as opposed to the heat being absorbed by the heat sink (the cold end of the chamber at ambient temperature).
If more heat is extracted as work than what actually reaches the heat sink, then theoretically, insulating the cold end of the displacer chamber against the external ambient temperatures would improve engine efficiency.
That is rather speculative, but I was also thinking that if what I have described above is true - i.e. that the heat is converted into work, then a Stirling Engine should operate cooler and be more efficient when under a heavy load doing some kind of actual work rather than just running without a load - not doing any work.
If heat is being converted into work then the more work the engine is made to perform the cooler it should run. Maybe the problem with many model Stirling engines overheating is that they are being run without a load of any kind and therefore the heat, rather than being transfered to the load on the engine to do work is just building up and causing the engine to overheat.
Perhaps this is already a known fact but for me it is something of a new realization and I'm wondering if anyone with more knowledge and experience in this area might be able to confirm or refute this supposition.
Thanks.
Tom
After ten years of additional research, study, engine building and experimentation, along with endless debate and controversy, on this and many other engineering, science, physics and "free energy" forums, I've come to the tentative conclusion that my intuitions, about how Stirling engines actually operate were correct.
Here is a simple, and hopefully easy to understand illustration.
An automobile that operates on petrol fuel, to travel up an incline, requires gas in it's tank to run the engine and overcome the downward pull of gravity.
After getting some fuel in it's tank, the car can accelerate up the hill until it runs out of gas. At that point, the engine stops, but the car may continue for a distance up the hill due to momentum. At this point the car, having spent all of it's fuel, and having used up all of it's stored momentum, stops, and unless the brakes are applied, the car will rull backwards, back down the hill to the gas pump for another refill of fuel.
Actually, due to stored momentum in accelerating back down the hill, the car will actually tend to travel further, bypassing the fuel pump. The distance it travels backward down the hill may be more than it traveled going up the hill
- IMG_20211209_113846657.jpg (101.65 KiB) Viewed 2012 times
This is an analogy of a Stirling engine's thermodynamic cycle.
The fuel pump for the car represents the heat supply for the Stirling engine. Heat is "fuel" for a heat engine.
The gasoline in the cars gas tank represents the heat that is transfered to the Stirling engines internal "gas" or working fluid.
The car itself is the piston.
The cars engine that turns fuel into acceleration or motion is representative of the expension of the working fluid. The burning or utilization of the fuel to do work.
Gravity that the car must work against to climb the hill, represents the outside atmospheric pressure that the Stirling engine must work against to drive the piston.
- IMG_20211209_113920429.jpg (90.29 KiB) Viewed 2012 times
Perhaps this analogy is not perfect in every way, but hopefully it will help to illustrate the principle, that contrary to former concepts of how a Stirling engine operates, like a car using fuel to climb a hill, the fuel is all completely used up by the time the car runs out of gas and starts rolling backwards. The gasoline does not have to be drained out of the cars fuel tank at the top of the hill to stop the car from moving so it can roll backwards back down the hill to "complete the cycle". By the time the car reaches the top of it's climb, the fuel is already long gone. In fact due to stored momentum, it went a little further than the fuel could take it.
Likewise, in a Stirling engine, it's fuel, which is HEAT, does not need to be let out or "rejected" in order for the piston to stop, reverse course, and be pushed back down the cylinder by atmospheric pressure. The fuel/heat, that was utilized to push the piston out, has already been used up in the act of so doing.. No heat has to be removed at the end of the power stroke of the Stirling engine, just as no fuel has to be drained from the car at the top of the hill.
Now it may be, due to poor engine design, that not all the heat gets utilized and to get the car to stop and roll back down for another fill-up, half a tank of gas has to be dumped out to stop the car to allow it to roll backwards, but such wastefulness is not at all necessary, and once this is realized, better engine design is possible.
