Effects of Pressure Altitude on Steam Engine Efficiency

[NW Mailing List]

Thank you very much for doing that!  I know that’s why they went to the pressure radiators in cars because the higher pressure increases the temperature that water boils. Also as you go up in elevation you have less oxygen to burn the fuel, but maybe in the less than 5000 feet elevation realm maybe it is minuscule at best. I know on takeoff I am burning 12000-13000 pounds of fuel an hour at 760 degrees ITT, but At cruise altitude I am sipping at about 5500 pounds of fuel an hour at 690 degrees because of the change in pressure/density altitude.

Maybe it was not even thought of at that time! Thanks for the insight!

Christopher J. Bunsey








> On May 28, 2021, at 8:53 AM, NW Mailing List via NW-Mailing-List <nw-mailing-list at nwhs.org> wrote:
> 
> Hi Christopher. I’ll take a swing at this. My initial thought on this is that given the boiler is a pressure vessel, atmospheric pressure would not come into play with regard to internal steam pressure or temperature. Externally, it would seem that at higher altitudes more combustion air would be have to move through the firebox to supply the same amount of oxygen for fuel combustion (for a given heat output). 
> 
> But that’s a layman’s point of view. I checked the book “The Steam Locomotive” by M.E. Johnson (Baldwin’s Chief Engineer), courtesy my dad’s library. Mr Johnson makes no reference to altitude from a boiler performance standpoint, which leads me to believe it wasn’t a substantial factor.
> 
> Matt Goodman
> Columbus, Ohio, US 
> 
>> On May 27, 2021, at 1:17 AM, NW Mailing List <nw-mailing-list at nwhs.org> wrote:
>> 
>> 
>> While on vacation on in AZ, we were paralleling some rails from Winslow to Flagstaff.  Knowing that water boils at a lower temperature at a relatively lower pressure, how did this principal apply to the operation and performance of a steam engine operating in lower pressure altitudes (higher elevations)?
>> 
>> Christopher J. Bunsey
>> 
>> 
>> 
>> 
> 
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