Future Trends in Commercial Aviation Engines’ Combustion - Novel Combustion Concepts for Sustainable Energy Development - page 151

problems are not encountered during technology development (viz. Bruce et al.
1977 , 1978 ). Nevertheless, the robust lean domes are F

3 safe; otherwise, they will
not be introduced as reliable aviation engines where safety is the primary design
criteria without any exceptions. The technologists and combustion product teams
have developed strong guidelines on the lean domes for safety; but that does not
mean that we should not look for alternatives to current premixing designs in
revenue service. Only a should ignore the fact that increasing takeoff pres-

sure ratio from 45 to 60 (viz. Table 5 ) may reduce the allowable mixing time by a
factor of 3 in addition to propensity to

“ fool ”

flashback. Therefore, this
section and the next two sections deal with lean dome concepts considered alter-
native to TAPS.

fl flameholding and fl

6.1 Swirl-Venturi Lean Direct Injection (SV-LDI)

The origin of the modern generation of single venturi lean direct injection concepts
(SV-LDI) can be traced to Tacina ( 1990 ) who discussed different options and
narrowed down to the basic con

guration investigated by many including the use of
axial swirlers by Tacina et al. ( 2005a ); radial swirlers by Tacina et al. ( 2005b ); and
discrete jets by Tacina et al. ( 2004 ). It is educational to see the similarity of these
three types of swirling flows to the primary swirlers of swirl cups presented earlier

in Figs. 3 , 4 and 5 ; but one should not make strong statements about the apparent
similarity because the geometrical details of the subsystems including the swirler,
venturi, injector, and its location can have big impact on overall emissions and
operability. The two most recent extensions to the baseline LDI con

fl

gurations of
Tacina et al. ( 2004 , 2005a ), known by LDI-2 are described in Villalva et al. ( 2013 )
and Tacina et al. ( 2014 ) which we will describe brie y here.

As shown in Fig. 41 , typical SV-LDI fuel/air mixer comprises of two elements,
viz. a converging/diverging venturi fed by a fuel injector with concentric axial
swirler with the vane angle optimized for meeting the requirements.
As shown in Fig. 42 , the baseline or LDI-1 has nine identical SV-LDI fuel/air
mixers arranged in a 3

fl

× 3 grid for testing in an adiabatic combustor with a square

Fig. 41 First generation of
swirl venturi lean direct
injection mixer (SV-LDI);
from Tacina et al. ( 2005a )