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 Post subject: Launch Engines - Steam Consumption
PostPosted: Wed Apr 10, 2013 6:29 am 
Full Steam Ahead
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Joined: Fri Nov 20, 2009 5:34 am
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Location: Phila PA USA
Boat Name: Margaret S.

Steam consumption of an engine can vary by wide margins, depending on the engine design, as well as steam inlet and exhaust conditions.

A well designed engine, with properly sized steam passages will give nominal performance. Multiple valve engines (Corliss Type), and even better, Uniflow engines, can use less steam per horsepower developed, assuming that these machines are properly designed and constructed.

Steam conditions also play here, generally higher steam pressure/temperature, and lower exhaust pressure, provides better efficiency. Steam superheat can significantly reduce engine steam consumption, as does high vacuum in the exhaust.

For small steam launch engines, these are the typical values:

Brake horsepower, ranging from 0.5 to 15 horsepower, with the great majority between 1 and 5 horsepower.

Main steam pressure, 75 to 150 PSIG, very little or no superheat

Exhaust conditions, atmospheric pressure or moderate vacuum.

Steam consumption is typically expressed in “Pounds per Hour” (PPH), and an approximate function, fairly good for typical steam launch plants, states that nominal steam consumption is 30 PPH plus 30 PPH for each horsepower produced.

For example:
A 1/2 horsepower steam plant would require 30 + 0.5 x 30 = 45 PPH

A 5-1/2 horsepower steam plant would require 30 + 5.5 x 30 = 195 PPH

These are nominal numbers, and a high efficiency steam plant might use only about 65% of the nominal steam consumption, while a more basic machine designed and built without efficient design could use 150% of the nominal values.

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