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I am having trouble finding reliable good data especially data that I know for a fact is good data that will work to build hot air engines from scratch that will actually run. I built an experemental displacer and displacer piston and also a power piston to experement with.

The displacer cylinder is several 20 ounce Chick Pea cans connected together end to end. Cans measure 3 3/8" diameter x 4 3/8" long. Displacer cylinder is 3.375" x 13 1/8" with a 1" long piece of 3/8" copper tubing attached to the side.

The displacer piston is two 15 ounce kidney bean cans connected together end to end. Cans measure 3" diameter x 4 3/8" long. The displacer piston is 3" x 8 3/4" with a 1/8" brass brazing rod attached to one end.

I put a pieces of water pipe in the lathe and bored out out smooth then made a brass piston to fit. The water pipe has a reducer fitting I reduced it down to 3/8" copper.

I connected the displacer cylinder to the water pipe with a section of rubber hose.

I put a thermometer on top and bottom of the displacer to monitor the temperature difference between the 2 ends.

I put a candle under the displacer and pulled the displacer piston up/down with the brass rod. The hole in top if a perfect fit for the brass rod. As I pump the displacer piston up and down air goes in and out of the hose pumping the power piston back and forth.

As the power piston goes back and forth I can measure the distance it travels. I should be able to build an engine now that I know how much the power piston moves back and forth for each stroke of the displacer piston. I can calculate the air volume in the system and the area and stroke of the power piston.

2 candles on the bottom of the displacer gives the power piston about 1/8" more stroke. A propane torch more than doubles the distance the power piston moves.

The cold end of the displacer cylinder gets hot after a few minutes and the power piston stroke startes to get shorter and shorter.

I can now calculate the total volume of air inside the closed system then using the data I have I should be able to build an engine from scratch that will work on the very first try.

I should also be able to scale this data up or down to make different size engines.

I also need to build another displacer with the same piston but a larger cylinder length so I can factor in a higher volume of air to see how that effects the stroke of the power piston.

It might even be good to buy a very low pressure guages to see if I can get a pressure reading from the pressure change inside the closed system.

I think with some more experenting I can collect enough data to make some performance graphs and come up with some really good information for designing my own engines from scratch.

I used some micky mouse material ( tin cans ) to build this I hope that does not effect the results of the data.

Sounds reasonable to me Gary. A manometer or tube filled with colored water should work for a gauge. 27.7 inches of water per pound. We use inches of water to measure draft (negative) in our furnaces at work (oil refinery) and to monitor our flare system pressure (positive). Very accurate.