Environmental Engineering Reference
In-Depth Information
Fig. 16 Characteristic LTO
NO
x
data of the Trent1000
and GEnx engines compared
against the CAEP/8 standards,
technology initiatives
'
(viz.
ERA and N+ 3) goals
has expressed its goals in a different manner, namely 50 and 30 % CAEP2 for AST
and UEET, 25 % and 20 % CAEP6 for ERA and N + 3 initiatives, respectively,
with the corresponding 30 OPR LTO values of 40, 24, 15, and 12; the latter not
much different from 15. However, these technology goals go with the corre-
sponding reduction in the regulatory NO
x
slope, viz. the slopes of the ERA and
N + 3 lines in Fig.
16
are 0.5 and 0.4, respectively, unlike the slope of 2 for the
regulatory standards after CAEP2, as shown in Fig.
16
.
Figure
16
also shows characteristic LTO NO
x
versus takeoff pressure ratio of the
Tren1000 (the lowest NO
x
rich dome) and GEnx, a second generation lean dome
combustor to be discussed in Sect.
3
. Also shown are the CAEP/8, regulatory
standards for large engines with OPR
s generally prefer to have 30 %
margin from the standards for at least its lowest rated thrust engines so that the
highest rated thrust engine does not have a margin lower than 10 %. The Trent1000
with OPR between 36 and 46 with the corresponding characteristic LTO NO
x
of 48
and 71 gm of NO
2
/kN thrust and 24 and 14 % margin from CAEP/8 barely meet
the desired limits. The GEnx with 35
≥
30. OEM
'
47 OPR and the corresponding NO
x
of 24 and
55 g/KN has margins of 66 and 39 % from CAEP/8, a considerable margin from the
future potential increased NO
x
stringencies. However, it appears that GEnx if
extrapolated to higher operating pressures may lose its advantage on margin rather
rapidly compared to rich-dome combustors. Unfortunately, neither power nor linear
extrapolations (viz.NO
x
¼
-
0012 OPR
2
:
78
0
:
¼
2
:
4846 OPR
64
:
645) provide rea-
sonable estimates as clear in Fig.
16
. Therefore, one needs to
find alternative lean
dome technology with considerably lower impact of pressure ratio than GEnx. With
OPR tending toward 60, OPR along with its higher T
3
, should one come up with
more robust lean dome technologies? Effect of P
3
and T
3
on ignition delay times
therefore needs to be discussed.
2.5 N + 2 and N + 3 Generation Engines
Challenges
'
As engines
operating pressures during takeoff increase along with no relief on the
minimum P
3
, T
3,
and FAR because of the operability requirements (Sect.
2.6
), the
'
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