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Rates of Combustion in Locomotive Furnaces. By R. A. Smart. 



The following brief comparisons of the rates of combustion in locomotive 

 and stationary furnaces, based upon data of tests made at the Purdue University 

 Locomotive Testing Plant, will show some of the effects of the heavy duty which 

 the limitations of space and the reijuirements of portability impose upon loco- 

 motive boilers. 



In stationary boiler plants, the usual rate of combustion is between the 

 limits of 8 to 20 pounds of coal per square foot of grate surface per hour. From 

 the record of the rate of combustion of over half a hundred boilers tested by Geo. 

 H. Barrus, a well known expert, an average of 11.5 pounds per foot of grate was 

 found, which may be taken as representing good practice. Under certain condi- 

 tions of speed and cut-off, it has been found that the Purdue locomotive, 

 "Schenectady," which is a fair representative of its class, consumes 2,670 jiounds 

 of coal per hour, while developing 520 indicated horse power. To consume this 

 ((uantity of coal economically at the rate given above would require a grate area 

 of 232 square feet. Taking 8 feet as the extreme allowable width, this would 

 give a furnace 29 feet long, which is of course much beyond the limits of avail- 

 able space. As the furnace of the Purdue locomotive has, however, only 17.5 

 square feet of grate surface, instead of 2S2, the rate of combustion under the con- 

 ditions mentioned above reaches the abnormal figure of 153 pounds per square 

 foot per hour. 



It has been stated by Isherwood that the evaporative efficiency of horizontal 

 return tubular boilers of ordinary design decreases as the rate of combustion 

 increases, and if this holds in stationary practice it may be taken, in a measure, as 

 applying to locomotive practice. From this it is apparent that where only 17.5 

 s(iuare feet of grate surface are provided to consume a quantity of coal requiring 

 over 200 square feet for economical combustion, thereby raising the rate of com- 

 bustion from 11.5 to 153 pounds per i-(juare foot, the evaporative efficiency will 

 necessarily be low. 



This extraordinary rapidity of combustion is still more striking when com- 

 pared with the conditions existing in an open fireplace. For instance, the rate 

 of combustion in an ordinary parlor grate is about 4 pounds per hour to the 

 square foot. At this rate it would require a grate equal in area to that of a room 

 26 feet sc^uare to consume the coal burned during the tests mentioned. 



Other comparisons may be made as follows: Stationary boilers are usually 

 allowed about 12 square feet of heating surface per horse power developed, while 

 the total heating surface of "Schenectady," about 1,200 square feet, allow.*, under 



