


(7080) 
XXIX.—On the Application of Graphic Methods to the Determination of the 
Efficiency of Machinery. By Professor FLEEMING JENKIN. (Plates XXVI.— 
2X XII.) 
(Read 18th February 1878.) 
Part Il.—The Horizontal Steam Engine. 
§ 31. In a previous paragraph (29) the loaded dynamic frame (fig. 38) for 
_ one position of a direct-acting horizontal steam-engine has been described, and 
the mode of drawing that frame explained, on the assumption that the loads 
L,, L,, L., La, are known : it was stated that these loads had been calculated 
for one particular engine. The present paper gives the varying effort which 
_ this engine is capable of exerting at each part of its stroke with given pressures 
(both constant and varying) in the cylinder, and given constant velocities of 
the crank-axle. The same calculations show the efficiency of the engine at each 
part of the stroke, and its total efficiency under the same circumstances. This 
problem has, it is believed, never hitherto been solved so as to take into account 
all the circumstances of mass, weight, and friction. 
§ 32. No pains has been taken in the choice of the particular example. The 
object of the paper is not so much to draw general conclusions as to all steam- 
engines—which, indeed, differ too much in arrangement to make this feasible— 
as to show how, by a method of no great complexity, full information can be 
obtained as to any particular engine or class of engines. 
The following are the particulars of the engine:—Stroke, 16 in.; dia- 
meter of cylinder, 8 in.; length of connecting-rod, 41 in.; centre of gravity 
of connecting-rod, 20 in. from the crank-pin; mass of connecting-rod, 34 lbs. ; 
mass of piston and piston-rod, 46 lbs.; mass of baianced crank and that part of 
the fly-wheel which is borne by the main bearings, 200 lbs.; the mass of the 
frame fixed to the earth is indefinitely large ; diameter of crank-shaft in bear- 
ings, 44 in.; diameter of crank-pin, 2:4’; diameter of pin at crosshead, 1°8”. 
The position of the resistance overcome (fig. 17, Part I.) is that of a tangent to 
an imaginary circle of 18 im. radius, concentric with the crank-shaft, the 
tangent being so inclined as to cut the centre line of the engine 19-2” from the 
crank-shaft centre on the side towards the piston. This line may be regarded 
as the direction of the resistance exerted at the teeth of a spur-wheel. The 
position of this line exercises a very material influence on the results obtained, 
which must not, therefore, as was said before, be considered as applicable to 
engines generally. The coefficient of friction has been taken as = +5. 
VOL. XXVIII, PART Il. 8 Xx 
