. Railway and locomotive engineering : a practical journal of railway motive power and rolling stock . as to the most eco-nomical boiler. The most economical boilermust have just as large heating sur-face as possible, especially in the firebox,and the combustion must be slower—thatis, combustion must be nearly perfect, andwith the present method of getting air tothe fire perfect combustion can only be fore, the smaller the boiler in proportionto work it must do, the less will be itseconomy. The rapid combustion in asmall boiler is produced by a contractednozzle, with the result that the backpr
. Railway and locomotive engineering : a practical journal of railway motive power and rolling stock . as to the most eco-nomical boiler. The most economical boilermust have just as large heating sur-face as possible, especially in the firebox,and the combustion must be slower—thatis, combustion must be nearly perfect, andwith the present method of getting air tothe fire perfect combustion can only be fore, the smaller the boiler in proportionto work it must do, the less will be itseconomy. The rapid combustion in asmall boiler is produced by a contractednozzle, with the result that the backpressure on the piston is very much in-creased ; the violent blast also causes con-siderable unconsumed coal to passthrough the flues, and, due to the greatervelocity of the gases, they are in contactwith the heating surface a shorter lengthof time. This has its influence in re-ducing economy. No locomotive boiler istoo large for economy if the above istrue. Hence, passenger locomotives forhauling heavy trains at high speedssliould have boilers as large as the weightof the locomotive will Tilt: SOLTIIERN UY obtained with slow combustion. Whenthe rate of combustion is high, the merepassage of the air through the fuel docsnot give an adequate mixing, when highefficiency is wanted. This is the reason,above all others, why forcing a boilerreduces its efficiency, and is the reasonwhy an engine with a small grate area,when forced, docs not give the efficiencyof a larger grate in which the coal isburned slower and the air has more timeto mix with the fuel. It is evident thatin a small boiler, that is, one in which alarge amount of steam has to be gen-erated in proportion to the heating sur-face, the fire muif be urged; and thcre- The Atlantic and Pacific type enginesgenerally have the most economical boil-ers. It is not uncommon for an engineof the Pacific type to have 2-in. flues 20ft. long, with 50 sq. ft. of grate area. Onthr
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