Future Trends in Commercial Aviation Engines’ Combustion - Novel Combustion Concepts for Sustainable Energy Development - page 108

their original objectives of achieving lower NO x within the speci ed design con-

straints including cooling technology. They were immediately followed by the 2nd
generation lean dome products known popularly as TAPS in GEnx in addition to
planned LEAP-X and GE9X. The takeoff NO x of GEnx is given by NO xGEnx = 1.079
×

2 = 0.991. These products will be able to meet the proposed
long-term LTO NO x regulatory standard within the generally accepted design mod-
i

10 -5

3.971

OPR W / R

nement process. TALON-X and recently introduced P&W TALON-
Axially Staged Combustion concept will provide credible alternatives to TAPS; an
interesting technologies competition. The 2nd generation lean domes produce an
order of magnitude lower exhaust smoke number than the rich domes. For all other
design requirements both the lean and rich domes have comparable characteristics.
The effect of FT fuel blends on combustion ef

cation and re

ciency and NO x is insigni cant; but its

bene ts in regard to particulate emissions are enormous in terms of both the number

density and mass emissions due primarily to signi cantly lower aromatic and sulfur

contents. Future CFD and semi-empirical model should be developed with the
proposed long term accuracy goal expressed in term of the standard deviation goal:

3% of takeoff NO x , 7.5 % and 15 % respectively of idle CO and HC emission indices.

˃

Keywords Rich-quench-lean (RQL) combustors NO x emission Alternative

-

fuels Reynolds-averaged Navier Stokes Flame temperature

1 Introduction

Figure 1 provides an appropriate start for this article because of the following
reasons. It introduces a new engine architecture involving fan-drive gear system
[known popularly as Geared Turbofan (GTF)] with attendant propulsion system
level impacts (Kurzke 2009 ). Compared to a ten fan bypass ratio (BPR), conven-
tional two-spool 103 kN rated thrust turbofan engine, it reduces the number of the
low-pressure (LP) compressor stages from 7 to 2, and that of the LP turbine (LPT)
from 9 to 3 for an optimum 5.9 LPT expansion ratio. Simultaneously it reduces the
LPT stage loading from 3.2 to 1.05 with attendant increase in its isentropic effi- -

ciency from 92.8 to 93.4 % which compares very well with 93.6 % of the present
day six BPR turbofan engines. GTF reduces LPT spool torque from 77 to 27 kN-m
with attendant smaller load for the fan-drive gear system. However, the LPT AN 2
increases from 6.7 to 41.9 m RPM

10 − 6 cant increase in the

mechanical design challenges; the corresponding value for the conventional six
BPR engine is 18.5. Both engines produce comparable takeoff thrust speci

× resulting in signi

c fuel
consumption (SFC) of 11.44 and 11.4 g/kN-s compared to 13.0 with the conven-
tional engines resulting 12.3 % reduction in the takeoff fuel burn. GTF gives
slightly smaller fan diameter (2.23 m) compared to 2.32 m but both are consider-
ably larger than 1.78 m of the current engines. It will lead to higher installation
losses without using advanced nacelle technology as implied in Fig. 1 . Furthermore,