Stirlingengineforum.com

Hi all,

I have built a double-acting pressurized gamma engine, with the intent to produce up to approx 1 hp. To date the most I have attained is about .2 hp at about 800 deg. F on the hot end and with water jacket on the cool side. The engine runs at 200-250 RPM no load at atmoshperic pressure. As I pressurize the engine the power increases to a point then levels off. As I increase the pressure the engine seems to "labor" as though it is working against itself.

My question to you is in regard to the volume ratios. I used the usual 1.5 : 1 ratio of displacer volume to power piston volume. I am wondering if that ratio may not be applicable to a pressurized engine? That is, should it possibly be more in the range of 2:1 or higher?

Your thoughts...

Thanks in advance,

Jon

I would think that you may be running out of efficient heat transfer, both at the hot and cold ends for a start. 200-250rpm sound very slow for a modern design, I would be looking at nearer to 1000rpm under load.
One place where you may have problems is friction, you maybe want to look at the seals on the crankshaft, this is a place where many people have trouble, the seal is OK without pressure, but as the pressure increases, so to does the friction. As far as the ratio between the displacer, and power piston, less rather than more would proberbly work better, the ratio is increased as the temperature goes down. Ian S C

Ian,

Thanks for the advice.

Jon

Jon

Like you I believe the double acting gamma offers many advantages and although I have yet to construct such an engine I have spent much time in preparation. I started by measuring the pressure changers on one of my engines using a laptop based osciloscope, then used this information to plot the pressures acting on both sides of the piston in a DA gamma at eight points in the cycle.

I found that the power output improved significantly when the phase angle between the displacers and the piston was set to nearer 45 to 50 degs.

I'm assumimg your engine is set nearer 90 deg phase angle, as is traditional, may I suggest you try reducing this angle.

GeoffV