5.2 EMISSION
The main emissions produced by an aircraft are carbon dioxide (CO2), carbon monoxide (CO), water molecules (H20), nitrogen (NOX) and unburned hydrocarbons (HC). The problems of emission are more complex than they are shown here incompletely.
The problems:
- CO2 is a main contributor to the greenhouse effect
- CO2 is a normal and unavoidable product of hydrocarbon fuel combustion
- Water vapour in the lower stratosphere influences chemical reactions and contributes to the greenhouse effect
- Contrails contribute to greenhouse effect
- H20 only recently identified as an pollutant
- NOX reduces ozone in the stratosphere and produces ozone in the troposphere
- Little progress achieved during last decades in reducing NOX
Possible constrains:
- Governments may introduce special taxes related to emission production (example : Sweden)
- Governments may limit air traffic volume
- Flight levels sensitive to H2O may be closed
Conventional solutions:
- Minimise aircraft weight and drag to minimise fuel consumption
- High thermal efficiency engine core
- High bypass ratio turbofan engines
- Flight Management System to minimise fuel consumption
- Detailed optimisation of conventional combuster
Advanced solutions:
- UHB ducted engines
- UHB Open Rotor engines
- Laminar flow wing and empennage
- Liquid Hydrogen fuel in terms of CO, C02 and HC
- Higher burn temperature
- Design aircraft for lower flight levels
- Special to reduce NOX
- Two stage burning
- Variable geometry combustor
- Twin combustor (idle/full trust)
- Pre mixing of air or fuel
- Low pressure ratio/combustion temperature
- Water injection
Problems arising from the UHCA:
- High emission concentration at smaller volume
Advantages with an UHCA:
- The Block fuel per seat is lower than any other aircraft
- The UHCA might get preferred landing access
- The UHCA uses latest state of the art aerodynamics
- The UHCA uses very high bypass engines (GE90)
- The GE90 dual-dome combustor reduces NO.
The benefits of technology on emission from aircraft during the last 30 Years are shown in the following picture:
Fig.: 5.3.1 Ref.: ICAO