1. Find the friction horsepower and the mechanical efficiency of a 12 in. by 15 in.
steam engine which gives the following test data:
area of the head-end diagram, 1.45 sq. in.; area of the crank-end diagram, 1.25 sq. in.; average length of diagrams, 3 in.; engine
speed, 240 rpm; indicator-spring scale, 80 psi; diameter of the piston rod, 2 1/2 in.; brake tare weight, 80 1b; brake gross load, 620
lb.; and length of brake arm, 2.63 ft.
2. A 15 in. by 21 in. steam engine with a piston rod 2 3/4 in. in diameter operates at 120 rpm to give the following data: area of the
crank-end diagram, 3.75 sq. in,; average length of diagrams, 3.5 in.; spring scale, 60 psi; length of brake arm, 63 in.; and net load at
the end of the brake arm, 1006 lb. Find the friction horsepower and the mechanical efficiency of the engine. 15.8 fhp and 88.5
percent.
3. A 16 in. by 14 in. double-acting simple steam engine with a piston rod 3 in. in diameter operates at 250 rpm to give an output of
200 bhp when 225 ihp are developed within the cylinder. (a) Find the friction horšepower and the mechanical efficiency the engine.
(b) The engine-indicator diagrams average 4 in. long and are taken with a spring having a scale of 80 psi. What are the diagram areas
if 5 ihp more are produced within the head end than in the crank end of the engine cylinder?
4. An 8 in. by 8 in. double-acting simple steam engine with a piston 1 1/2 in. in diameter is rated at 35 bhp when operated at 350
rpm with an initial steam pressure of 250 psia. The engine valve setting is such that equal amounts of power are developed within
the two ends of the cylinder to give a mechanical efficiency of 87.5 percent when the rated power is produced. (a) Find the actual
mean effective pressure developed within each cylinder end. (b) Find the area of each indicator diagram if they average 2 in. long
when taken with a spring having a scale of 160 psi. (c) Find the net load necessary at the end of a Prony brake 63 in. long?
5. A steam engine develops 100 bhp under the following conditions: initial steam pressure, 135.5 psig; barometric pressure, 29.6 in.
of mercury; initial quality of steam. 0.99; exhaust pressure, atmospheric; and total wet steam used per hour, 3450 lb. Find the
engine steam rate and the thermal efficiency.
6. A steam engine operates with steam at 140 psia initial pressure and a total temperature of 400 F, a back pressure of 5 psia, a load
of 350 ihp, and a total steam consumption of 6950 lb per hr. Find the steam rate and the thermal efficiency based on indicated
horsepower. 19.85 lb per hr and 11.75 percent, Answer
7. A steam engine operates with 500-bhp output, a steam consumption of 15 lb. per bhp-hr., an initial steam temperature of 450 F,
an initial steam pressure of 200 psia, and an exhaust pressure of 3 in. of mercury abs. Find the thermal efficiency based on brake
horsepower, the Rankine efficiency, and the engine efficiency.
8. A steam engine delivers an output of 300 hp under the following conditions: initial steam pressure, 180 psia; exhaust pressure,
2.46 psia; initial steam temperature, 400 F; mechanical efficiency, 88 percent; and steam consumption, 12 lb. per ihp-hr. Calculate
the thermal efficiency based on brake horsepower, the Rankine efficiency, and the engine efficiency.
