Choosing ALPHA Cycle Ratios

[Bumpkin]

Vamoose, I think understanding Alpha compression ratios is the problem. After a bit of playing on graph paper, it looks like a 90 degree phased twin with the same displacement cylinders and moderate length rods (to minimize deflection) will have about a 5-1 compression ratio - accounting for absolutely no dead space. Add in one cylinder's worth of exchanger/regenerator/dead space, and compression ratio is still 2-1. You'd certainly want to avoid having to design in more dead space to get the compression ratio low enough. One neat thing about 90 degree "V" twins is that they are easy to balance (vibration-wise,) but an advantage of a two-throw crankshaft would be that you could use the same size cylinders and pistons, and vary the displacement ratio with different crank throw and rod length - or you could easily vary the 90 degree phase a bit to one side or the other to affect compression ratio also.

P.S Sorry for showing up in your neighborhood again - I don't bring out the best in some folks.

[vamoose]

Geoff,
Chastised I am (but I don’t mind). Cant help myself, The dreaming is the the trappings of my inquisitive nature. Have been reading lots of different things and trying to take it all in, it can get a bit confusing (and I can be a bit slow on the uptake). The view from the hill is a lot different to that in the valley. Its a winding journey.

Anyway, thanks for helping point me in the right direction. The less mistakes now the easier it will be in the long run. this is my first attempt at building a stirling engine and i'm having trouble pinning everything together in my head. I’m more of a tactile learner (monkey see monkey do), and have no direct stirling experience to call on. Am still waiting for that epiphany. I sometimes find it hard to process what I'm reading about, even though it may be apparent to others (its been politely suggested to me that I'm a bit of a late bloomer), I will slowly piece it together.
Please don't think your efforts are in vain. Your help so far has been invaluable. I'm going back over the stuff I have from you. I will take a few steps back, and take some time to ponder it some more.
vamoose

[vamoose]

Bumpkin,
Yep, Alpha compression ratios is definitely one of my problems. I would love to be able to sit down and do as you have just done for me (thanks!!). Could you possibly direct me to a website or some literature that could assist me, in layman's terms, in learning how to do this?
vamoose

[Bumpkin]

Layman's terms is all I got, and I don't know any definitive equations. For what it's worth, this is what I did: Make a series of simple two-dimensional drawings of a 90 degree "V" twin - it relates to any other 90 degree phased arrangement. Put pistons in their relative positions in the cylinders, relating to crankpin location in various stages of crankshaft rotation. Assuming a flow connection between the tops of the cylinders, it can be seen that with a displacement ratio of 1-1, minimum displacement occurs when the crankpin is pointed at the saddle of the "V" between the cylinders. Maximum displacement is when the crankpin is pointed away from the "V". Compression ratio is simply the difference expressed as a ratio between max. And min. Add in the dead space to both max. and min. to determine the actual overall compression. This only applies to the 1-1 displacement ratio. Other ratios would shift the max. and min. points one way or the other - but once you visualize the modelling, you can come close. I like graph paper, but there are probably a zillion better ways. Bumpkin

[Ante]

hello

I want to say that maximum compression ratio of alpha engine without regenerator is 5.7:1

excel file for analysis if some want to see...