Hello all, I have been working on redrawing a set of plans of a compound condensing steam engine that I downloaded from the CSEE forum. I am scaling up the original plans by 1/3. In drawing them in a CAD system the piston only has about .045" clearance between the head and piston on either top or bottom. My question is: if I lengthen the cylinder so each end has say 1/4" clearance, will that adversley affect performance? It seems to me that .045" is just too close. Also at that close the piston will block the cylinder drains at full stroke. Any thoughts? Thanks in advance.
steam engine design?
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aonemarine
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Generally speaking, to achieve a efficency in a steam engine you want low clearance. increasing the clearance at TDC will decrease efficency, but you can make it up with recompression. At lower rpms High recompression tends to hurt power output but at higher rpms seems to increase efficency and performance. What valve style are you dealing with?
Philjoe5
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I scaled up a Ray HasBrouck mill engine by 25% and 50% a few years back. The original design had 0.095" clearance at each end of the cylinder in this double acting design. I simply scaled everything up by a straight multiplier so in the scaled up versions I had 0.119" and 0.143" at each end of the cylinder. Plenty of room for a drain port. Here's the 1.25x scale at TDC
I've run both engines on air and steam at model shows for many trouble free hours.
Now comes big questions - since you bypassed the introduction of yourself (a faux pas you can easily correct
).
What do you plan to do with your completed engine, just run it for show, or try to get useful work out of it?
Was the original engine designed to be run on steam to produce a working engine?
If you're going for max efficiency then keep the dead volume to a minimum. Angle drill the drain port so it just clears the cylinder bore at each end but gives you adequate room for a valve.
Phil
I've run both engines on air and steam at model shows for many trouble free hours.
Now comes big questions - since you bypassed the introduction of yourself (a faux pas you can easily correct
). What do you plan to do with your completed engine, just run it for show, or try to get useful work out of it?
Was the original engine designed to be run on steam to produce a working engine?
If you're going for max efficiency then keep the dead volume to a minimum. Angle drill the drain port so it just clears the cylinder bore at each end but gives you adequate room for a valve.
Phil
This is a non working volume of wasted steam at best.
This dead space serving in turn for the steam admission and exhaust, undergo temperature changes causing condensation highly detrimental to the performance.
However, on a mechanical point of view, a small proportion of dead space is good owing to its cushioning action on the piston at higher speed specialy at the bottom side of a vertical engine.
1/4" seems hudge, I would keep the clearance under 10% of the stroke, including the cylinder steam passages.
you have to modify the drain holes...
This dead space serving in turn for the steam admission and exhaust, undergo temperature changes causing condensation highly detrimental to the performance.
However, on a mechanical point of view, a small proportion of dead space is good owing to its cushioning action on the piston at higher speed specialy at the bottom side of a vertical engine.
1/4" seems hudge, I would keep the clearance under 10% of the stroke, including the cylinder steam passages.
you have to modify the drain holes...
