Stirlingengineforum.com

Hi.

Can someone please help me. Im looking to change the phase angle on a Stirling engine, but im unsure exactly how to explain what is being altered. Would it be fair to say the compression ratio inside the engine is altered, because im not sure this is the right way of explaining it.

Perhaps heat transfer cycle, or something like that?

Id really appreciate on your input to help explaining this.

James

I think he means the angle between the displacer crank and the power crank, usually 90 degrees.

As for explaining it, I have no idea sorry. Anti equilibrium angle perhaps ? ?

Hi.

Sorry for not being speicific enough. Im refering to changing the 90dgeree phase angle between the displacer and power piston. I am trying to figure out what exactly will be altered inside the engine, if I was to make this 80 degrees for example.

Ian is right. The best way to do this is on a test platform.

The reason there is 90 degrees of lag between the displacer and the drive piston is because of the type of motion that the displacer makes, as a result of the crank shaft. The crank shaft causes a sinusoidal motion: It moves fastest at the center point of its motion path and it moves slowest at each end of the motion path. Based on a combination of factors such as rpm, heat transfer rates, and dead air space, the maximum heating seems to occur about 90 degrees after the peak of the heat cycle. Any of those factors can cause the position of the best phase angle to change in either direction. The only way to really know for sure is to do some tests as Ian described.

There are a few displacer designs that do not use the sinusoidal motion path at all. They use mechanisms that move the displacer quickly to the opposite end and then rest there momentarily. James Senft shows a couple of mechanical linkage variations to do this. I do a similar thing in my designs using magnets.

According to some of the research I've read, the range is about 80 deg. to 120 degrees. The 120 deg. phase angle makes for an easy start engine, but reduced power yet higher efficiency. From what I have gathered, 90 degrees is best for an engine, the others are for cryocoolers. Read the information about 1 year ago, and the information was stored on another computer at the time.

I did have it explained, but it got wiped out in a bit of chaos that occured a wee while ago.
Generally 90deg is the phase angle between the displacer and the power piston. The motor can be tuned by altering the angle. First get the motor going at its best at 90 deg., mark the shaft and crank, adjust by moving the crank no more than 5 deg, then test, you really need a tacho and a brake to measure torque,keep moving the crank in the same direction until the performance falls. Now go back to 90deg, and move the crank the other way. Remember to note down all the angles, and the performance at each angle. You may find that you go from 80 to 110deg. The reason for measuring the torque is that it is possible that the maximum power is not at maximum revs, and by measuring both you can work out the power in watts.
Watts= rpmx torque (in oz)divided by 1352. Or watts=grm/cm x rpmx.00001026. Ian S C

The angle between pistons is an experience datum.
In Stirling engine is maintained a natural pulsation from hot to cold site.
The coerence of the mechanical system movements and natural pulsation allows the extraction of energy.
In Stirling-Ringbom engine the displacer is free, and moves individually dragged by the wave pressure, according to said natural pulsation.

The successive possible step is the movement, governed by an actuator (magnet), of the displacer, and this would give a significant ability of government to the rotation of the engine.
Although I think that, with all the other physical characteristics not essentially modified, (geometric, pressures and heat content of gas) that determine the natural frequence, you can go easily out the natural pulsation, and to fall quickly in reduced efficiency.