Bits I collected when my characters were discussing the possibility of using steam engines.
---------------
small gasoline engine to steam: (2 cycle is simple; 4 cycle needs another lobe on the camshaft)
www.instructables.com/convert-a-lawn-mower-engine-to-steam-or-air/===================
Formulas for steam engine horsepower:
www.smokstak.com/forum/showthread.php?t=148858The PLAN formula can be used to calculate the theoretical or ideal horsepower a steam engine can produce.
HP = PLAN / 33000
HP - horsepower
P - average pressure in the cylinder (often estimated at 1/2 the boiler pressure) 50psi (from 100 psi boiler?)
L - length of the stroke in feet 0.16667 (Honda 6HP gs engine)
A- area of the piston in square inches 5.72265
N - number of power strokes per minute 3000
If the engine is hooked up to some type of dyno (a Prony brake for example) and the power it produces is measured, the efficiency of the engine can be determined. 4.335HP (requires camshaft modification) 30psi gives 2.6HP (needs same mod)
===============
I have a spreadsheet that does the PLAN calculations: www.jecarter.us/files/steam-engine-hp-calc-PLAN.xls================
Maybe this will help?
On page 43 of the CASE Steam Engine Manual: To show the application of this formula, we will take, for example, an engine with a 9” bore, a 10” stroke, a speed of 250 rpm, and a boiler pressure of 150 lbs., the size of the 50 horse-power Case engine.
P = 50% of 150 = 75 lbs.
L = 10 / 12 or .833 feet.
A = 9 x 9 x .7854 = 63.617 sq. in.
N = 250 x 2 = 500 strokes per minute. (That is, 500 working strokes per minute.)
Substituting these values for the letters in the formula above, it becomes:
75 x .833 x 63.617 x 500
----------------------------- = 60.2 horse-power
~ ~ ~ ~ ~ 33,000
Since this is the power developed by the steam in the cylinder, it represents the indicated horse-power which is greater than the brake horse-power by about 10 per cent. Subtracting 10%, we have 54 brake horse-power as the result. (.90 x 60.2 = 54.18 h.p.)
============
A VERY quick rule of thumb for engines in the smaller sizes is..
diameter squared divided by 4.
Thus my 4" diameter cylinder Sears-Roebuck engine calculates in at 4 horsepower.
My 3" diameter "BF Knowles" launch engine figures in at 2-1/3 horsepower (9/4)
The rule of thumb applies to: throttling engine, typical 19th century pressure of say 85 to 100 psi boiler pressure max, typical 19th century rpm of 150 to 250, and a smaller size (8" or smaller diameter) range.
Of course this rule of thumb says NOTHING about stroke, or RPM, or Mean Effective Pressure. A Stanley automobile engine with 3" bore would put out upwards of 30 horsepower at 600 psi boiler pressure. And a corliss engine at 12 inch bore would put out in real life 100 horsepower but according to the rule is good for 144/4 or about 36 horsepower?
===============
Many like to resolve the HP expression down to its lowest/greatest form. Then it fits the fundamental "foot pounds" designation of 33,000 lbs lifted 1 foot high each minute. I find it easier to go back to Watt, who, measuring mine lifting horses winching up coal and water, came up with 150 lbs lifted 220 feet per minute. Or 2.5 miles per hour. Seems more tangible and easier to think about in actual work terms.
=============
