I decided to try to make an engine similar to the one in this video, but a little bigger in order to use up some of the material left over from the Moriya project. The video includes a sketch of some of the parts, but it is more or less illegible, so I combined what I could figure out from the video with information from other sources to create a plan I hope will work. Here's some of what I was thinking along the way, including links to those other sources:
- The displacer OD will be 1" to match some stainless steel tubing left over from the Moriya project.
- Based on the 1" displacer OD, the working piston OD will be 0.46" according to the guidelines given here: http://techref.massmind.org/techref/mem ... anson.html
- The stroke will match the working piston diameter, according to the guidelines given here: http://www.w-haag.de/mansonmotor.htm
- The displacer piston length will be 3 times the stroke, so the air is forced away from the temperate middle portion of the displacer cylinder and into the hot and cold ends. This is sort of a guess on my part, but it follows the Moriya design.
- The displacer piston cap will look about like the equivalent Moriya part.
- The displacer cylinder ID will be 1-1/16", according to the guidelines given here: http://techref.massmind.org/techref/mem ... anson.html
- The displacer cylinder length will be the displacer piston length, plus the stroke, plus a little extra to make sure the displacer piston doesn't bump against the ends of the cylinder.
- The power cylinder will be bushed with bronze or brass.
- An insulating spacer will provide thermal isolation between the hot cap and the cold end. The spacer will be centered on the displacer cylinder length.
- The hot end will be generally modeled after the Moriya hot end.
- The cold end fins and such will be generally modeled after the Moriya cold end.
- The bearing supports, crankshaft, and connecting rod will be generally modeled after the corresponding Moriya parts.
- The connecting rod must be long enough (relative to the stroke) to limit sideways forces on the piston and also to result in (somewhat) sinusoidal piston motion. According to internet folklore, the connecting rod length should be somewhere in the neighborhood of twice the stroke, or longer. Longer is better (up to a point), so let's say it's three times the stroke.
The following pictures show the internals and make it easier to describe how the engine works. The first thing to notice is the power piston. It's hollow, and has four little holes in the bottom such that the pressure inside the piston is always the same as that inside the displacer cylinder. Then on the left side of the power piston there are two openings. These line up with holes in the power cylinder when the piston is at top dead center and bottom dead center.
To understand how the engine works, consider the picture immediately above. Imagine that heat is being applied to the bottom of the displacer cylinder, and that the crankshaft is rotating clockwise. The pressure inside the displacer cylinder and the piston will increase, driving the piston and displacer upward. At the same time, more and more of the air will be displaced into the hot end, where it will get heated and increase the pressure even more. Until ...
Boom. When the piston reaches top dead center, one of the holes in the piston will line up with the vent hole in the cylinder and the pressure inside the engine will immediately fall to that of the surrounding atmosphere. As the crankshaft continues to rotate clockwise (due to inertia), the piston and the displacer will be forced downward. This will in turn force the air from the hot end of the displacer cylinder into the cold end. As the air cools, the pressure inside the engine will drop, creating a suction that will help further to pull the piston downward. Until ...
Boom (again). When the piston reaches bottom dead center, the other hole in the piston will line up with the cylinder vent hole and the pressure inside the engine will immediately rise to that of the surrounding atmosphere. Inertia will then cause the piston to start rising again and the cycle will repeat.
That's the theory, anyway. If anybody sees something that looks wrong or missing from all this, or something that could be improved, I'd love to hear about it. I still need to make some working drawings before I can actually cut up any metal. So it's definitely not to late to make changes.
-- Russell Mac