Environmental Engineering Reference
In-Depth Information
0303PR
1
:
9722
. Therefore, the ratio of lean to rich-dome takeoff NO
x
EINO
xRD
L
¼
0
:
10
4
OPR
2
, which means that the ratio of NO
x
at 35 OPR of 0.4 succes-
sively increases to 0.72 and 1.07 as OPR increases to 45 and 55. In other words, the
relative advantage of lean domes over rich domes diminishes with increasing OPR
unless one can introduce the next jump in lean technology, namely TAPS1 into
TAPS2, TAPS3, and eventually TAPS4.
The TAPS technology team was able to demonstrate the feasibility of TAPS2 on
a sector rig (viz. Lee et al.
2013
) identi
is 3
:
56
ed as N + 2 in Fig.
27
. As clearly stated by
the TAPS team in Lee et al. (
2013
), TAPS2 design required more than 70 %
combustion air with enhanced fuel/air mixedness along with
“
signi
cant challenge
to both operability (combustion ef
The latter
requires the use of high-temperature ceramic matrix composite and advanced liner
cooling. Because of the continuous tradeoffs among low NO
x
, cruise combustion
ef
ciency and dynamics) and durability.
”
ciency, combustion instability, and autoignition, the TAPS2 technology devel-
opment effort started with the down-select process from the 13 con
gurations tested
in the single-element
flame tube rig.
In order to make TAPS technology suitable for products, there were two addi-
tional objectives that were clearly met as shown in Fig.
27
. First, make successive
technology development for increasingly higher engine pressure ratios without
corresponding increase in takeoff NO
x
. The data from the CFM-TAPS engine
technology demonstrator and full-scale annular rig data for the AST-TAPS clearly
demonstrate the viability of the
fl
first objective. It should be reminded that all the
three applications use approximately 70 % combustion air.
The second objective was contrary to the prior lean dome low-emission tech-
nology development experience, in that the number of nozzle tips increased relative
to the rich domes in the
first generation lean domes. Each nozzle tip of the rich
domes was replaced by two tips in DAC
s including the CFM56 and GE90 DAC
products. The dry low-emission LM6000 product has 75 tips compared to 30 with
the water-injected diffusion
'
flame combustor (Fig.
53
) which will be discussed later.
Other OEMs have also used more nozzle tips than rich-domes in their lean dome
technology programs (viz. Bruce et al.
1977
,
1978
,
1981
; Dubiel
1986
; Rizk and
Mongia
1990
; Roberts et al.
1977
; Sanborn et al.
1983
; Segalman et al.
1993
). As
expected, the lean dome fuel/air mixing devices are more complex than rich domes,
viz. Figs.
5
,
6
,
25
and
26
. Therefore, the former
fl
s unit production cost should be
higher than the latter until new cheaper manufacturing technology (viz. additive
manufacturing technology) matures. Therefore, the second objective of TAPS
technology development was to have fewer lean mixers than the swirl cups used in
the comparable engines and simultaneously emit 50 % lower LTO NO
x
emission.
For example, GEnx with 22 tips in higher thrust class engine (viz. 255
'
-
345 kN)
than its predecessor CF6-80C2 engine (viz. 231
273 kN) with 30 swirl cups. We
were glad that this objective was met as shown in Fig.
27
. However, for the
technologist there is one more point to remember: the CF6-80C2 engine
-
is takeoff
EINO
x
ranges between 22 and 29 whereas that of GEnx is between 15 and 48.
Combustion product person can take pride in claiming victory in regard to LTO
'
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