Steam Consumption of Engines.

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Steam Consumption of Engines.

Post by csonics » Wed Nov 18, 2009 5:02 pm

Posted on behalf of fredrosse:

fredrosse
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Posted: Tue Oct 23, 2007 6:13 pm Post subject: Steam Consumption of Engines.
Back in the late 1800's, the term "Boiler Horsepower" was established, based on the then modern engines (simple counterflow slide valve engines), which typically consumed 30 pounds of steam per hour for production of each output horsepower. The nominal steam pressure was 70 PSIG, with engines exhausting to atmosphere. One "Boiler Horsepower" boiler heat output corresponds to 33,475 BTU (British Thermal Units) per hour. This standard is still used today in the heating and process industries.

The engines used to establish this standard were generally much larger (20 - 80 HP) than typical steam launch engines (1 - 5 HP), and the smaller engines tend to use much more steam per output horsepower than their larger cousins.

Some Actual Data:

Live Steam Magazine had a detailed series describing tests of a good simple counterflow engine producing about 1/4 HP output. This engine used about 20 PPH (Pounds per Hour) steam, 100PSIG, slightly superheated.

4-1/2 HP Poppet Valve Uniflow Engine, 1000RPM, 135 PSIG Saturated Steam, 100 PPH Steam Flow. This is about as good as it gets for a small engine.

The Walking Beam Engine I have built will have a boiler capacity of 100 PPH for 1 HP output. This engine has generally lower efficiency, being a counterflow engine operating at low speed. I expect it to use about 80 PPH steam at rated output.

A rough steam consumption for a typical simple launch engine is probably around 50 pounds of steam per hour for each output horsepower. Compound engines and condensing to a good vacuum will reduce steam consumption.
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