Modern Engineering Thermodynamics

13.15 Lenoir Cycle 493
Exercises
28. If the isentropic pressure ratio in Example 13.10 is increased from 2.85 to 3.10, determine the resulting compressor inlet
and exit pressures. Assume all other variables remain unchanged. Answer: p 2 = 0.500 MPa and p 3 = 1.55 MPa.
29. If the minimum volume V 3 in the Ericsson cycle engine in Example 13.10 is decreased from 3.0 × 10 –3 m 3 to
1.00 × 10 –3 m 3 , determine the new compressor inlet pressure and volume (p 2 and V 2 ). Assume all other variables
remain unchanged. Answer: p 2 = 0.500 MPa and V 2 = 0.00285 m 3 .
30. A modification of the Ericsson cycle engine proposed in Example 13.10 calls for increasing the power piston outlet
pressure and the compressor piston inlet pressure from p 1 = p 2 = 0.500 MPa to p 1 = p 2 = 1.00 MPa. Determine the new
Ericsson cold ASC thermal efficiency resulting from this design change. Assume all other variables remain unchanged.
Answer: (η T ) Ericsson cold ASC = 22.3% (no change).
13.15 LENOIR CYCLE
Both the Stirling and the Ericsson cycles are for external combustion with thermal regeneration. Initially, an
appropriately sized furnace was used as their heat source. This made these engines rather large and awkward,
and even though they could theoretically achieve high (reversible) thermal efficiencies, the mechanical and thermal
irreversibilities of the early engines were very large; consequently, they had rather low actual operating thermal
efficiencies. In 1860, the French engineer Jean Joseph Etienne Lenoir (1822–1900) made the first
commercially successful internal combustion engine. He converted a reciprocating steam engine to admit a mixture
of air and methane during the first half of the piston’s outward (suction) stroke, at which point it was
ignited with an electric spark and the resulting combustion pressure acted on the piston for the remainder of
the outward (expansion) stroke. The following inward stroke of the piston was used to expel the exhaust gases,
then the cycle began over again. This cycle is (ideally) composed of only three effective processes: constant
volume (combustion), constant entropy (power), and constant pressure (exhaust), as shown in Figure 13.42.
1
1
T
3,4
Q H
V = c
p = c
s
(a)
s = c
2s
Q L
W E
p
s = c
3 4
2s
V
(b)
Fuel
and
air
Ignitor
(c) Intake (3 to 4)
(d) Ignition (piston at
midstroke 4 to 1)
(e) Power (1 to 2s)
Ignition coil
Spark
Battery
(f) Exhaust (2s to 3)
(g) Ignition system
FIGURE 13.42
The Lenoir cycle.