Are there any tables or charts which would show how much adding superheating to a steam locomotive would increase its horsepower and or tractive effort?
In the conventional formula for tractive effort, the effective pressure is taken as 80% of the nominal boiler pressure for locomotives without superheaters and 85% for those with superheaters. So for locomotive with the same characteristics the tractive effort is 6.25% higher with superheating.
Fuel economy was often quoted as 10% to 20% better.
On hilly routes, superheated locomotives were allowed 10% greater loads by some railways.
M636C
Two observations based on my research driven by a very similar question of my own:
As superheaters were being introduced in the United States, Baldwin Locomotive contended that a modest level of superheat would deliver better results overall than the Schmidt designs, which allowed higher temperatures. That position turned out to be indefensible as more and more railroads in North America, led by the Canadian Pacific, followed European practice. By the 'teens, the prevailing wisdom was "the hotter the better" and the operator would accept higher maintenance costs.
During the 'teens, several railroads followed the Railroad Age Gazette's calculations that credited each square foot of superheating surface as 1.5 times the equivalent amount of evaporative heating surface.
Both of these measurements suggest that it was the percentage of superheater area to the total that counted most. The higher that percentage, the more power per cylinderful of steam one could extract. Thus, the adoption of Type E superheaters, which were more complex and required more maintenance, was driven by the desire to dry out the steam as much as possible.
Were these engineers correct in this view? Can't say for sure. I've seen some tonnage-rating assignments that indicate that some railroads believed they gained a considerable increase in effective tractive power with relatively high degrees of superheat. But later designs also increased direct heating surface as much as possible, so the relative contributions of bigger fireboxes and superheat can be difficult to untangle.
The use of a high degree of superheat in locomovitives resulted in a reduction of 25-35% in fuel and 35-40% in water for the same power output. Horsepower capacity was increased from 15% at lower speeds and up to 45% at higher speeds, drawbar pull being similar.
The main advantages of superheat is the fact that superheated steam has greater specific volume than saturated steam for a given pressure, and the elimination of condensation.
This link below shows a graph comparing Atlantic types with and without superheat:
http://books.google.com/books?id=sBBCAQAAIAAJ&dq=increased%20capacity%20superheated%20steam%20locomotives&pg=PA841#v=onepage&q=increased%20capacity%20superheated%20steam%20locomotives&f=false
"If a nation expects to be ignorant and free, it expects what never was and never will be." Thomas Jefferson
Looking over Hollingsworth's compilation of express passenger steam locomotives, Chapelon went to a high degree of superheat area -- about 40% of evaporative area -- but the Russian designs went as high a 50% (i.e. 2000 sq ft evaporative, 1000 sq ft superheat area on their "C" class 2-6-2). Strange locomotives those Russian designs, not particularly high boiler pressure but champs in superheat.
Hollingsworth suggests that steam locomotive design garnered a great deal of scholarly attention from academia in Russia, and maybe moderate boiler pressure with insane levels of superheat was an optimal design in some sense.
If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
if i remember correctly, superheat does NOT affect the starting tractive effort. it boosts the HORSEPOWER and efficiency giving rise to better uphill or accelerative performance - just like an NYC hudson will out-race a very similar NYC pacific with identical starting TE.
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