An Engine Simulation Program                                                                         

I've been thinking about a new Stirling engine project that uses a fan to blow cold air through the regenerator into the hot space and visa-versa. The vessel would contain a plastic bag to keep the hot and cold air from mixing.

Simulation Program. Click for bigger view.

I wrote a VB6 simulation program that (I hope) models what happens when the engine runs. The program calculates the instantaneous torque produced by the engine for each degree of movement of the flywheel. For each position of the flywheel, I know the piston volume , the vessel volume, the dead space volume and the total volume of the engine in cubic inches. Also for each position of the flywheel, I know the ratio of hot and cold air in the vessel and I can calculate what that associated hot/cold air volume would be if it were unbound so as to expand (or contract) it’s volume to keep the air pressure at an ambient 15 PSI. From the ratio of the total volume and the unbound volume I calculate the pressure in the vessel that fluctuates positively and negatively about the ambient pressure each cycle. The force on the piston head is calculated, as is the torque delivered to the flywheel by the connecting rod. It turns out that a wheel driven by a connecting rod does not exactly follow a sinusoidal curve. With a bit of creative programming I think I now accurately calculate the reciprocating piston position and the true force the connecting rod imparts tangentially to the flywheel.

Pressure-Blue,     Force-Red,     Torque-Green

Because  power is transferred to the flywheel as the air is expanding and again as the air is contracting, two peaks per cycle are seen on the torque curve (green). For bigger piston volumes, the torque can momentarily become negative, although curiously, the average torque is still larger than for a smaller piston.

Torque-Green ,  2nd Torque Curve-Orange,   Sum-Purple

If two of these engines are coupled at a phase of 90 degrees, then the torque curves add to make a relatively constant positive torque value. I 

incorporated torque curve: duplication, offset, summation and scaling functions, into the program by mouse clicking on the graph. There are a lot of bells and whistles in this program and I believe it does a good job of simulating the kind of engine I have in mind to build. You may download the simulator from the following link. It is called RabbitSimulation.exe.

https://docs.google.com/file/d/0B9fsJB6CcZqrVW9fMVBEVVJTZVE/edit?usp=sharing