Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
produced over the ICAO landing/take-off cycle, which is intended to represent typical aircraft
operations in the vicinity of the airport. The mass of each species (in grams) is divided by the
take-off thrust of the engine (in kilo Newtons) so that different size engines can be reasonably compared; thus, the resulting units are g kN-1. ICAO landing/take-off
cycle, measurement procedures, and emissions standards are discussed further in Section 7.7.1.
Table 7-4: Typical basic performance and operational requirements of a modern aircraft engine combustor.
Item Requirement Value Max/Min
1 Combustion efficiency
- At takeoff thrust (%)
- Idle thrust (%)
2 Low-pressure light-off capability (MPa) 0.03 (Max)
3 Lean blowout fuel/air ratio (at low engine power conditions) 0.005 (Max)
4 Ground light-off fuel/air ratio (with cold air, cold fuel) 0.010 (Max)
5 Total pressure drop-compressor exit to turbine inlet (%) 5.0 (Max)
6 Exit gas temperature distribution
- Pattern factor
0.25 (Max)
- Profile factor
0.11 (Max)
7 Combustion dynamics [dynamic pressure range/inlet air pressure (%)] 3 (Max)
8 Liner metal temperature (K) 1120 (Max)
9 Cyclic life to first repair (cycles) 5000 (Min)
Table 7-5: Combustion developments linked to emissions performance.
Requirements* Emissions Implications and Compromise Required
1, 8, and 9 Lowering of liner cooling flows improves "idle" efficiency (low HC and CO) and ability to reduce NOx but must be balanced against
effect on liner temperatures and life/durability
2, 3, and 4 Wide range of fuel/air ratios and long dwell times in combustor favor good light-off performance but must be balanced against need
to control HC and CO emissions at low power and NOx formation rates at high power
5 and 7 Low overall and dynamic pressure losses required to minimize SFC losses but must be balanced by need to retain good mixing for
low emissions and good liner cooling
6 Long mixing lengths improve exit profiles and pattern factors but require more cooling air and increase NOx formation times
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