Getting ready to produce an engine

[me___7720]

I am getting ready to produce my first Stirling engine. I think I am
going to do an alpha. The basic engine I want to use is pictured here:

http://picasaweb.google.com/oddssodds/Stirling

I have some basic questions:

1. How much volume should I leave between the piston and the cylinder
cap, at TDC?


2. Can anyone direct me to more specific plans for a regenerator.
What is the relationship between the regenerator and the cylinder size?

3. With a 375cc hot cylinder, how much heat should I be applying,
given the cold cylinder is running with a water jacket and a radiator?

4. Am I wrong in making the assumption that the greater the heat
differential, the greater the power put out by one of these units?

5. Is there any sort of valving in the regenerator system?

Thanks everyone,

Paul

[bptdude___2569]

Beautiful metal work pics.
I have envy.


There is a piece of software from one of the government labs that runs simulations, I forget where, but may be able to find it. I will post if I dig it up. The number were beyond what I wanted at the time.


for your questions:

"4. Am I wrong in making the assumption that the greater the heat differential, the greater the power put out by one of these units?"

You are totally right. You want the hot to be as hot as your fuel source will allow to make it still practical, and your pretty metal machine can stand.

Don't forget the cooling side. This is a common mistake. You don't have to think of it in inernal combustion engines. The shrinking of gas volume is very much affected by the cold side, yielding well power.


"5. Is there any sort of valving in the regenerator system? "

well, not by current designs.
*wink*
The regenerator is a mystery people usually only think they really understand. It is usually a passsive element, often steel wool being used in model engines, and various metal honeycomb design that fill Stirling patent applications for commercial models.

People argue about it origially being used for greater power output, or for better fuel usage.

The short version, is that a certain level expansion and deflation of gas is required to make the Stirling go properly. If you can heat the hot side enough, and cool the cold side enough, you can do without the regenerator more than people think. Ideally, you want the gas to expand quickly, at the right time, in the hot section, and you want the gas to cool quickly, at the right time, in the cool section.

Putting heat on the outside of the metal casing is the most common means of heating the inside, which to me is totally silly. I'll leave it at that.

Best wishes, and I hope other people jump in to help you. Just between you and I, the alpha will be the piston type model to go big, as it allows advanced control of the hot and cold sides, which will overcome the extra machinery, and function with high power, like an internal combustion.

[me___7720]

thanks for the reply. i hope you can find that simulator

those engine blocks are amazingly cheap. with the crank and pistons, you are only talking about 150 dollars US.

if you want the referral, i can let you know where to get them.

[iron_goober]

I know cast iron and, I can't remember what the metal is, I thought it was brass or bronze, can run dry in the cylinders without the need for lubrication. You could put a sleeve of brass into the bore and then use a cast iron piston on the cold side, I'm not so sure it would work on the hot side, because of expansion ratios, but for the cold side it should work well if you want an oil-less engine. Can you pressurize those crank cases? That would definitely be an advantage.

What sort of heat source are you using? It is hard to calculate the amount of heat you need to put into your engine, because based on the heat transfer rates and mechanical losses, this will affect the engine speed, which further affects the heat transfer rates. Many parameters are required to closely calculate the output power and required heat input, and even good models are still off on the calculation.

I would be interested in where you got those engine blocks if you don't mind sharing the information.