Jerry C posted: -
Reason for increased bore, I've got a lot of steam and a proper superheater not a drier. However unlike I/C I have no idea about the relationship between bore and stroke as it applies to steam engines. The bogstandard has a smaller bore than the TVR1A but a larger stroke. I guessed that if I made the bore similar that I would be able to swing a larger prop with more pitch.
Hi Jerry,
The torque produced is a function of force x radius (force being working pressure x piston area and Radius being half the stroke), therefore a longer stroke engine will produce more torque than an engine having the same bore but shorter stroke at the same working pressure.
The shorter stroke engine will have the higher speed(rpm) band.
For driving a large prop the slower long stroke engine will be the best solution.
Increasing the working pressure will have the same effect as increasing the bore whilst keeping the stroke the same... providing the boiler can deliver the steam required at the increased pressure.
A stroke of 2 x bore is probably about as High as is generally feasible for small model engines... any higher and condensation losses begin to have a huge effect... unlike full size, where stroke can be 4 or 5 times the bore... as with Mississippi sternwheelers, however, these generally used wet steam at relatively low pressure and relied on the wet steam for lubrication... you can't get away with this using superheated steam.
Go easy on using super heat...
1, displacement lubricators don't work very well with even mild superheated steam.
2, Brass and Bronze are more prone to galling at the higher temperatures... especially if the lubricator is compromised.
Superheating is completely unnecessary for this type of engine as it is effectively a non expansion design... the piston valve does not have any lap and is designed to allow simple reversing by swapping the inlet an exhaust pipes, in the same way as an oscillating engine... a mild steam drying would be more than adequate.
To make use of steam expansion you need to cutoff the steam input at part stroke, say 55% or less, and allow the steam to expand for the remainder of the stroke... but, even this would not be the best use of superheated steam if both cylinders were the same dimensions.
Superheating only comes into it's own when used with a double, triple or quadruple expansion engine having early cutoff at say 45%, and with the exhaust from each cylinder passing to the input of the next, with the final cylinder exhausting into a partial vacuum... usually combined with a true condenser.
I would not recommend using superheated steam with this engine... it serves no real purpose and can compromise lubrication... it will also increase the wear factor of your piston o-rings.
If you must use superheat, make it mild, and even then a good mechanical injection lubricator would be a better, and Safer, solution... as used on model steam locomotives and traction engines.
Have a good bike race and enjoy the outdoor exercises.
Best regards.
AlexC aka Sandy.
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Topic: Jerry C does some turning & milling and builds a new steam plant. (Read 92857 times)