Future Trends in Commercial Aviation Engines’ Combustion - Novel Combustion Concepts for Sustainable Energy Development - page 110

temperatures 200 ° C hotter than the CFM56. GTF ' s gas temperatures are projected

to be 60 ts of lean

domes over rich domes for NO x emissions. It is interesting to note that a second
generation twin-annular premixing swirl-stabilized

- 130 ° C lower than LEAP. etc. ” ), then we must reassess the bene

flames (TAPS), TAPS II will be
used in the three LEAP engine models, namely LEAP-1Afor the A320neo, LEAP-
1B for the B737 MAX, and LEAP-1C for the Comac C919 with more than 5,600
LEAP-X engine orders and commitments as of October 31, 2013 according to the
Snecma website (Snecma 2014 ). If LEAP-X takeoff pressure ratios are comparable
with that of the GEnx with TAPS which gave the characteristic landing

fl

takeoff
(LTO) NO x of 35 % CAEP6 at 35 OPR but increased to 59 % CAEP6 at 47 OPR
compared to TALON-X claim of achieving 50 % CAEP6 as shown in Fig. 1 , this
may set into motion another round of innovations in the GE lean dome products.
The combustion system durability including

-

fl flashback, autoignition, and

fl flameholding within the premixing mixers become more challenging to manage as

OPR levels exceed 45. Therefore, alternative mixer technologies need to be
explored for the N + 2 and N + 3 cycles (Lee et al. 2013 ; Mongia 2013e ; Tacina
et al. 2005a ; Tacina et al. 2014 ).
This article therefore gives an overview of the current rich-dome combustion
system design, requirements, and challenges (Sect. 2 ), followed by the first alter-

native to rich domes that have been successfully introduced as products (Sect. 3 ),
the lowest levels of achievable NO x (so-called entitlement) as determined from
small-scale rig testing (Sect. 4 ), summary of recent engine emissions data with
“ alternative fuels (Sect. 5 ), description of the second alternative to rich-

dome products (Sect. 6 ) that may be of interest to the OEM

green ”

s for the N + 2 and
N + 3 generation aviation engines; a brief discussion on the modeling and corre-
lation accuracy expectations from future efforts in this area (Sect. 7 ), and the third
alternative to rich domes which was shown promising for autoignition times closer
to 0.2 ms in Sect. 8 . Finally, a short section on operability and dynamics is followed
by Summary, References, and Acknowledgments. Limited by the page count
normally associated with any article, most of the material presented here is from the
author

'

s personal experience, and this should not be misinterpreted by the reader for
lack of relevance and/or respect for the outstanding quality works conducted by
numerous combustion research, technology, and product development teams.

'

2 Current Combustion System Designs and Challenges

2.1 Modern Rich-Quench-Lean Combustors RQL

Figure 2 shows a typical cross-section of a modern rich-dome aviation engine
combustor along with its major subcomponents including diffusion system that
reduces the compressor discharge Mach number by a factor of 1.3 - 2.0 before

dumping the flow and dividing it into three annular streams, respectively, for the

dome, outer, and inner annuli around the combustion chamber with the

fl