Modern Engineering Thermodynamics

Problems 533
72. Determine the value of the cutoff ratio that causes the Diesel
cold ASC thermal efficiency to become zero for an engine with a
20.0 to 1 compression ratio. Assume k=1.40.
73. A Diesel cycle internal combustion engine has a compression
ratio of 15.0 to 1. At the beginning of the compression process,
the pressure is 14.7 psia and the temperature is 520. R. The
maximum temperature of the cycle is 4868 R. Determine the
cold ASC thermal efficiency. Assume k=1.40.
74.* A two-cylinder, two-stroke Diesel cycle internal combustion
engine with a 16.2 to 1 compression ratio and a total
displacement of 1.50 L burns kerosene having a heating value
of 40.0 × 10 3 kJ/kg when using an air–fuel ratio of 25.0 to 1.
The intake temperature and pressure are 100. kPa and 15.0°C.
When the engine is running at 1200. rpm and producing
6.00 kW of power, determine (assuming k=1.40) the engine’s
a. Cutoff ratio.
b. Cold ASC thermal efficiency.
c. Indicated power output.
d. Mechanical efficiency.
e. Actual thermal efficiency.
75. The Atkinson cycle is similar to the Otto cycle except that the
constant volume exhaust-intake stroke at the end of the Otto
cycle power stroke has been replaced by a constant pressure
process in the Atkinson cycle, as shown in Figure 13.70. Q H
occurs during process 4s to 1, and Q L occurs during process 2s
to 3 in each case.
a. Sketch the T–s diagram for the Atkinson cycle numbering
and labeling all the process path lines as in the p−V diagram
of Figure 13.70.
b. Determine the Atkinson cold ASC thermal efficiency for
k=1.40, T 1 = 8000. R, T 3 = 520. R, and CR = v 3 /v 4s = 8.0.
Design Problems
The following are open-ended design problems. The objective is to
carry out a preliminary thermal design as indicated. A detailed design
with working drawings is not expected unless otherwise specified.
These problems have no specific answers, so each student’s design is
unique.
76. Design a small, single-cylinder, piston-type steam engine and
boiler that can be used to power a toy vehicle, such as a train or
a tractor. Choose a convenient fuel such as alcohol, and design
the boiler so that it can supply enough steam to your engine.
Make sure the boiler has a pressure relief valve, and pay close
attention to other safety considerations.
77. Develop a preliminary design for a closed loop Rankine cycle
steam power plant to be used in a compact automobile. The
prime mover may be either a reciprocating piston or turbine and
must produce a net output of 40.0 hp with a thermal efficiency
in excess of 35.0%.
a. Specify inlet and outlet states for the boiler, prime mover,
condenser, and boiler feed pump.
b. Choose typical values for the isentropic efficiencies of the
prime mover and boiler feed pump, and calculate the overall
thermal efficiency of the power plant.
c. Specify the fuel to be used in the boiler.
d. Estimate the overall power plant weight, including fuel
storage.
e. Specify conditions needed to meet part-load operation and
prime mover speed control during vehicle acceleration and
deceleration.
f. Specify all additional equipment needed to connect the
prime mover output shaft to the vehicle drive wheels.
78. Design a small, single-cylinder Stirling or Ericsson cycle external
combustion engine that can be used to demonstrate the
operation of this type of engine in the classroom. Choose a
convenient fuel such as alcohol. Provide detailed working
drawings and a thermodynamic analysis.
79. Design a Brayton cycle power system to propel a small drone
aircraft that will be used for military target practice. The fueled
drone must weigh less than 500. kg, and since these aircraft are
not reusable, they must be produced at minimum cost.
Determine or specify the air mass flow rate, pressure ratio,
compressor and turbine isentropic efficiencies, turbine inlet
temperature, thrust, thrust to weight ratio, exhaust temperature,
and hot ASC thermal efficiency. A computer program will help
you carry out parametric studies of the variables involved.
80. Design a personal exercise machine that uses the otherwise
dissipated human exercise energy in some productive way.
For example, the exercise energy could be converted into
mechanical, chemical, or electrical energy, which could then
be used in some domestic device (for example, to power a
computer, TV set, or kitchen appliance). Another solution would
be to design a system that would feed the exercise energy
directly into the local electrical power grid for credit against the
1
1
s = c
p
4s
V = c
s = c
2s
V = c
3
p
V = c
s = c
4s
s = c
3
p = c
2s
V
Otto cycle
V
Atkinson cycle
FIGURE 13.70
Problem 75.