Future Trends in Commercial Aviation Engines’ Combustion - Novel Combustion Concepts for Sustainable Energy Development - page 127

ratios of peak to minimum P 3 and T 3 increase with attendant challenges on dura-
bility of the combustion structure and fuel injector. Moreover, for a given thrust
class of engines, increase in takeoff pressure and bypass ratio to improve the overall
system ef

ciency will lead to smaller high-pressure core size with several impli-
cations for the combustion system design options. Smaller engines generally will
have fewer number of fuel nozzles, smaller combustor length and channel height
with attendant higher surface to volume ratio and therefore requiring higher fraction
of combustor air for cooling and more challenging pro

le and pattern factor issues.
This will therefore lead to higher combustion temperatures which will make it
dif cult for lean domes to have lower NO x . Therefore product versions of the basic

advanced cooling technologies with potential cooling flow reductions up to 80 %

(viz. Acosta 1987 ) as described in Anon ( 1982 ), Nealy et al. ( 1985 ), Paskin et al.
( 1990 , 1993 ). Here we provide two

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figures in order to make summary statements.
Nealy et al. ( 1985 ) share their advanced cooling technology experience which is
further illustrated by a simpli ed Fig. 17 from Acosta ( 1987 ). The conventional

film-cooled liners relative to the baseline called splash film have large design bands

in regard to the range of reduction in cooling flow as it can be attributed to several

design factors including dome mixer/injector design features. Johansen et al. ( 1977 )
made convincing illustrations for managing impact of

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flame streaking without
which almost all advanced schemes will not realize their full potential. Convective
film cooling coupled with transpiration cooling schemes have the potential for
reducing cooling

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flow requirement up to 70 %, again with a wide scatter band.
Further reduction in cooling

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flow rate can be realized by minimally cooled ceramic
structure, a technology still in TRL3 stage for combustor application. Technological

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Fig. 17 Conventional film cooling including splash flame (SF) performance in terms of reduction
in cooling flow rate versus liner temperature for different advanced cooling schemes including

convective film/transpiration, transpiration (TRANS), counter

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flow film cooling (CFFC), compliant
matrix composite (CMC), and ceramic matrix; reproduced from Acosta ( 1987 )

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