PISTON AND CRANK EFFORT DIAGRAMS 325 
_ of connecting-rods, 48 inches, Weight of reciprocating parts (including piston, 
= and cross-head), high pressure, 1082 Ibs. ; intermediate pressure, 
; low pressure, 1523 lbs. Weight of each connecting-rod, 953 lbs. Angles 
cranks, 120°. Sequence 
ks, (1) high pressure, (2) ad -+-4-4 
te pressure, (3) low .. , / 
pressure. Speed, 275 revolutions ~~ d 
per minute. 20 
_ Indicator diagrams taken from 
the engine at ? load are givenin 49 ‘ 
0 
Figs. 505, 506, and . The 
- copect are in lbs. per square 
above or below the pressure 
of the atmosphere. The dotted Intermediate Pressure. 
line diagrams are for the under Fia. 506. 
sides oes gy 
(a) ¢ y enlarge the indicator diagrams, making the length of each 4 
inches, and take for pressure scales, 1 inch to 30 Ibs. per square inch for the high 
pressure, 1 inch to 10 lbs. per 
square inch for the intermediate 
,and 1 inch to5lbs,per 0° — poe oI ; 
uare inch for the low pressure I-F ~ q 
8. 
6) Reconstruct all the dia- 
ogee except that for the top of 
high pressure piston to show 
ures per square inch of the 
p of the high pressure piston, 
to a scale of 1 inch to 30 lbs. per 
square inch. [For example, the 
area of the bottom of the inter- 
mediate pressure piston is 2°18 Low Pressure. 
times the area of the top of the Fic. 507 
h ton, therefore eo? 
the heights of the diagram for the bottom of the intermediate pressure piston 
must be enlarged 2°18 times to correct for area of piston, and they must be reduced 
in the ratio of 30 to 10 to correct for pressure scale. The height of the resulting 
diagram will therefore be 2-18+3, or 0°73 of the heights of the corresponding 
diagram in (a).] : 
(ec) Reconstruct the diagrams in (b) on a straight base to show effective 
on the respective pistons. 
(d) Correct the diagrams in (c) for the weight and inertia of the reciprocating 
, reduced to per square inch of the top of the high pressure piston, includ- 
in the weight of the reciprocating parts half the weight of connecting-rod. 
(e) Draw the polar and rectangular diagrams of crank effort for each crank. 
(f) Draw the polar and rectangular diagrams of combined crank effort. 
(g) Determine the mean combined crank effort in lbs. per square inch of the 
top of the high pressure piston. 
(hk) Determine the positions of the high pressure crank, measured in degrees 
in direction of motion from the top d centre, for minimum and maximum 
he 
Ss @ ® b 
(i) Determine the coefficient of fluctuation of energy for this engine under 
the given conditions. ; 
17. The following particulars * refer to a 400 horse-power Crossley gas-engine. 
There are two cylinders, with their open ends facing one another and their 
connecting-rods working on a crank common to both. Diameter of cylinders, 
26 inches. Stroke of pistons, 3 feet. Length of connecting-rods, 6-707 feet. 
Speed of crank shaft, 150 revolutions per minute. 
Total weight of fly-wheel and accessories, two crank slabs, two balance 
weights, crank pin, equivalent rotating part for two connecting-rods, and engine 
* The particulars for this exercise are taken from the Proceedings of the 
Institution of Mechanical Engineers, 1901. , 
