Modern Engineering Thermodynamics

532 CHAPTER 13: Vapor and Gas Power Cycles
Regenerator
6
5
Fuel
1
4s
Compressor
Q regen
W net
T
Combustion
chamber
1
Turbine
2s
4s
3
5
6
2s
3
s
FIGURE 13.69
Problem 59.
and the turbine inlet temperature is 2500.°F. Using the hot air
standard cycle analysis, determine the:
a. Net work output of the cycle in Btu/hr and MW.
b. Hot ASC thermal efficiency of the cycle.
62. An internal combustion engine operating on the Otto cycle has
a pressure and temperature of 13.0 psia and 70.0°F at the
beginning of the compression stroke (state 3 in Figure 13.48)
and a pressure at the end of the compression stroke of
200. psia. For the cold ASC with k = 1.40, determine
a. The compression ratio, CR.
b. The temperature at the end of the compression stroke.
c. The thermal efficiency of the cycle.
63. An eight-cylinder, four-stroke Otto cycle racing engine has a
4.00-inch bore and a 4.00-inch stroke with a compression ratio
of 10.0 to 1. Find the mean effective pressure in the cylinders
when the engine is running at 5000. rpm and burning fuel at a
rate of _Q fuel = 1.00 × 10 3 Btu/s. Assume k=1.4.
64. Determine the actual brake horsepower produced by a fourstroke
Otto cycle internal combustion engine operating with
a 7.50 to 1 compression ratio and a mechanical efficiency
of 30.0% when the combustion of the fuel is producing
225,000 Btu/h inside the engine. Assume k=1.40.
65.* Air enters an Otto cycle internal combustion engine at 90.0 kPa
and 15.0°C. The engine has a compression ratio of 8.00 to 1.
During the combustion process, 3000. kJ per kg of air is added
to the air. Assuming a reversible engine, determine
a. The pressure and temperature at the end of each process of
the cycle.
b. The engine’s cold ASC thermal efficiency.
c. The mean effective pressure of the engine.
66. Determine the output brake horsepower of a small two-stroke
Otto cycle internal combustion engine that has the following
characteristics:
Displacement = 5:00 in 3
Speed = 2000: rpm
Compression ratio = 8:00 to 1
Air−fuel ratio = 15:0 to1
Mechanical efficiency = 30:0%
Fuel heating value = 18:0 × 10 3 Btu/lbm
Ambient conditions = 14:7 psia and 70:0°F
67. A dynamometer test of a six-cylinder Otto four-stroke cycle
engine with a 231 in 3 displacement gave the following results at
4000. rpm:
Indicated power output = 250: hp
Actual ðor brakeÞ power output = 75:0hp
Heating value of the fuel being used = 20:0 × 10 3 Btu/lbm
Fuel consumption rate = 54:0 lbm/h
Determine
a. The mechanical efficiency η m of the engine.
b. The ASC thermal efficiency of the engine.
c. The isentropic compression ratio (CR) of the engine,
assuming an Otto cold ASC.
d. The mean effective pressure (mep) inside the combustion
chamber.
68. Professor John L. Krohn at Arkansas Tech University is running
an engine test. At the beginning of the compression process in a
hot air standard cycle, Otto cycle, the conditions are p 1 = 14.7 psi,
T 1 = 77.0°F. The compression ratio is 8.50 and the pressure
doubles during the constant volume heat addition. For this
cycle, use the air tables (Table C.16a) to determine the
a. Heat addition per unit mass.
b. Net work per unit mass.
c. Hot ASC thermal efficiency.
d. The maximum temperature reached in the cycle.
69.* At the beginning of the compression process in a hot air
standard Diesel cycle, the conditions are p 1 = 1.00 bar, T 1 =
25.0°C, V 1 = 700. cm 3 . The engine has a compression ratio of
18.0 and the heat addition per unit mass is 920. kJ/kg. For this
cycle, Professor John L. Krohn at Arkansas Tech University wants
you to use the air tables (Table C.16b) to determine the
a. Maximum temperature reached.
b. Cutoff ratio.
c. Net work.
d. The hot ASC thermal efficiency.
70. A Diesel cycle internal combustion engine has a compression
ratio of 18.0 to 1 and a cutoff ratio of 2.20. Determine the cold
ASC thermal efficiency of this engine. Assume k = 1.40.
71. Show that, as the cutoff ratio of the Diesel cycle approaches
1.00, the Diesel cold ASC thermal efficiency becomes equal to
that of the Otto cycle with the same compression ratio.