Modern Engineering Thermodynamics

13.21 Diesel Cycle 513
to stroll on deck. He was in the best of health, in very cheerful spirits, and had expressed most sanguine expectations as to
the future of his engine and the development of the company. 12
12 Ten days later, the crew of the Dutch boat Coertsen came upon the corpse of a man floating in the sea. The body was in such an advanced state of
decomposition that they did not bring it aboard. Instead, the crew retrieved personal items (pill case, wallet, pocket knife, eyeglass case) from the clothing
of the dead man and returned the body to the sea. On October 13, these items were identified by Rudolf’'s son as his father’s. No one knows for sure how
or why Diesel went overboard. Some believe he committed suicide because of his numerous “breakdowns,” and some believe he was murdered by either
fellow Germans (who resented his lack of nationalism) or by coal industrialists (who resented his engine).
T
3
4s
v=c
v=c
Q H
1
2s
Q L
W out
p
4s 1
3′
s=c
s=c
2s
3
p
3′
4
1
2
3
s
V
V
(a) T−s diagram
(isentropic cycle)
(b) p−V diagram
(isentropic cycle)
(c) p−V indicator diagram
(actual cycle)
Combustion (4s to 1)
and power (1 to 2s)
Exhaust
(2s to 3 to 3′)
Intake
(3′ to 3)
(d) The operation of a four−stroke Diesel cycle engine
Compression
(3 to 4s)
FIGURE 13.53
The Diesel air standard cycle.
The thermal efficiency of the Diesel cycle is
where (see Figure 13.53a), for the hot ASC,
ðη T Þ Diesel = ð _W out Þ net
_Q H
= _ Q H − j _Q L j
_Q H
= 1 − j _Q L j
Q H
j _Q L j = _mðu 2s − u 3 Þ and _Q H = _m½ðu 1 − u 4s Þ + pðv 1 − v 4s ÞŠ = _mðh 1 − h 4s Þ
Then, the thermal efficiency of the Diesel hot ASC is
For the Diesel cold ASC, this becomes
ðη T Þ Diesel
= 1 − u 2s − u 3
h 1 − h 4s
hot ASC
ðη T Þ Diesel
= 1 − c vðT 2s − T 3 Þ
c p ðT 1 − T 4s Þ = 1 − T 3ðT 2s /T 3 − 1Þ
kT 4s ðT 1 /T 4s − 1Þ
cold ASC
(13.35)
For the isentropic processes from 1 to 2s and from 3 to 4s, we have
and
T 2s /T 1 = ðv 2s /v 1 Þ 1−k
T 3 /T 4s = ðv 3 /v 4s Þ 1−k = CR 1−k