Scaling Up

[paul]

I'm just starting to think about what engine I'm going to build to go with my new boiler. I realise that's probably an odd way of going about things but what the hey!

I've already built one very simple horizontal oscillating engine but this time I'm thinking double-acting vertical or maybe even a 'clapper' type engine.

Thing is, I'd like to scale things up a bit but I'm not sure what constitutes 'sensible' scaling - probably because I have no idea how to calculate the power requirements vs boiler size. In simple terms, what sort of relationship should there be between the boiler and the engine it is powering? For example, is it feasible to run an engine with a 10mm dia cylinder with a stroke of say 40mm off a boiler with a capacity of maybe 150ml?

Various plans I've looked at mention scaling up but this invariably applies to the engine only.

Any thoughts, ideas, suggestions most welcome.

Once this cold spell finishes and my concrete floored garage is inhabitable again I am expecting some progress!

[SteveW]

Paul,

I've seen formula (loosely) linking grate area to engine size. The concept being engine output (size??) being limited by the amount of heat available to generate steam to push it round i.e. how much coal can burn at any one time.

You then get into issues of how much steam before a water top-up or how long to boil/return to boil which takes you boiler volume.

[dscott]

Dear Paul,
One of my current projects is for a very simple 4 wheel De winton loco in 5" gauge, using a double expansion verticle driving to the front wheels. By using a 5" dia boiler, you are kept on your toes as to steam production. A 6" dia can be fitted thus being a little more powerful and relaxing to drive. For a smaller boiler gear up the engine 2 to 1 and have some fun.
david.

[chris vine]

Hi Paul,

What length and diameter is your boiler. Length of the water space that is.

I will try to suggest a size of cylinder which could work well. There is nothing more frustrating than a boiler which runs out of steam after a few seconds!

Chris.

[havoc]

I must say I find a stroke of 40mm for a 10mm diameter cilinder excessive. If you use full pressure, you will need a lot of steam, and with expansion it would become also problematic because the very large expansion ratio.

A stroke of 20mm would be more conventional.

The loc I made has a 10mm diameter, 15mm stroke single acting cilinder with a 50mm diameter boiler that is 100mm long (inside dimensions). This works very well. Haven't measured boiler capacity.

But as said before, the volume capacity determines how long you can run. It is the heating capacity that will determine if it will work.