ORAL ESCRITA

The combustion of kerosene in aircraft engines is directly coupled with the amount of carbon dioxide and water produced. Other exhaust products are sulfur dioxide, nitrogenous oxides, carbon monoxide, hydrocarbons and soot. The basis for the calculation of emission factors are so-called emission indices (EI). The EI is defined as the mass of a substance in grams per kilogram of fuel burned.

Fuel Content Dependent Emissions

Due to its nearly constant carbon to hydrogen ratio (a good approximation for the average sum for-

mula is C12H23) the combustion of one kilogram kerosene results in about 3150 g carbon dioxide (CO2)

and about 1240 g water (H2O). The emitted amount of sulfur dioxide (SO2) is exclusively dependent

on the fuel sulfur content. The international threshold for sulphur in kerosene is 0.3 M% (3 gS/kgkerosene) resulting in 6 g/kg SO2. The figures in Table 7-5, however, reveal that the current sulphur

content in kerosene is assumed to be significantly lower, between 0.025 M% and 0.05M%. In this study, we employ the latter figure, which is in line with the figure given in Jungbluth (2003) and Unique (2002). In contrast to Borken (1999) no distinction for long and short haul is made. Further- more, in Borken (1999), an emission index for HCl emission of 2E-05 g/MJ (8.6E-04g/kg) is pre- sented, based on the Cl content of diesel fuels.

Combustion Process Dependent Emissions

The production rates for other emissions such as nitrogenous oxides, carbon monoxide (CO), hydro- carbons (HC) and soot, are strongly dependent on the combustion process, i.e. on the type of aircraft

In general, these emissions are measured in engine test facilities at sea level static conditions. Due to changes in ambient conditions and influences of increased speed, aircraft engine tests under sea level static (SLS) conditions are not appropriate to determine the emissions for in-flight situations. For the measurements in combustor test facilities the combustor parameters assigned to the in-flight conditions are commercially sensitive and often not available. The measurements at simulated in-flight conditions in an engine altitude test facility are very expensive. Real in-flight measurements (performed out of a window of an aircraft during flight or by a chase aircraft in behind) are complicated and expensive, too. Therefore special calculation procedures (so called correlation methods) have been developed. These correlations base on all kinds of measurements and are suitable for the determination of the amount of emissions depending on engine type and operating condition.

In Table 7-5 emission indices as can be found in the recent literature for the main pollutants and CO2

are summarised.

Table 7-5: Emission indices for the main pollutants and CO2

1: Lufthansa (2001), figures represent a modern fleet 2: Jens Borken et al. (1999), values represent long haul flights 3: Unique (2002), figures from the Airport Zürich

4: Dings et al. (2002), figures represent the long haul flight and for NOx the figure represent the cruise phase. The

reverse development of NOx and HC emissions can be explained with fuel consumption reductions, which are

mainly achieved due to higher combustion temperatures, resulting in a more complete combustion of hydrocar- bons to CO2 and H2O and an increased formation of NOx.

5: Andreas Döpelheuer (2001), figures represent typical flight conditions.

6: Methane and NMVOC are calculated by employing a methane share of 5% of total HC emissions Jens Borken et al. (1999)

7: In line with Frischknecht (2003)

For the LTO cycle, a specific VOC profile is available from Shareef et al. (1988). It has been stated that the VOC profile varies with the trust setting of the aircraft, and therefore on the actual operation stage of the aircraft (cruising, take off, etc). In the absence of further information we apply this split to all stages.

Emission Specific emission [g/kg fuel]

Lufthansa (2001) 1 IFEU (1999)2 Short haul IFEU (1999)2 Long haul UNIQUE (2002)3 CE (2002)4 State of the art aircraft CE (2002)4 Today’s average aircraft DLR (2001)5 This pro- ject CO2 3145 3182 3182 3170 3150 3150 3150 3150 CO 2.5 5.59 3.6 1 - - 3.7 3.7 SO2 0.5 0.6 1 1 0.6 0.6 - 1 NOx 15.2 15.9 15.9 12.5 15 12 14 14 HC (VOC) 0.49 1.4 1.4 0.5 1 0.3 1.1 - 7) NMVOC 1.33 1.33 1.05 6) CH4 0.07 0.07 0.05 6) H2O 1240 1240 1240 N2O 0.03 0.03 0.03

Table 7-6: VOC species profile for aircraft engine emissions, based on an average LTO-cycle.

Benzene Formaldehyde 1,3 Butadiene Ethylene Total share on

VOC

Unit % VOC % VOC % VOC % VOC % VOC

LTO-average 1.9 15 1.8 17.4 36.1

Location of Emission

Airborne emissions of aircrafts open a new, third dimension since they are released in troposphere and stratosphere.

The cruise phase of most present-day passenger aircrafts takes place in an altitude range (8–13 km) that contains portions of the upper troposphere and lower stratosphere IPCC (1999). Because these two atmospheric regions are characterized by different dynamics and photochemistry, the placement of aircraft exhaust into these regions must be considered when evaluating the impact of exhaust species on atmospheric ozone. A clear distinction of the share of emission released into two atmospheric re- gions is complicated due to the highly variable and attitudinally dependent character of the tropopause. (i.e., the transition between the stratosphere and troposphere). Comparisons of aircraft cruise altitudes with mean tropopause heights has led to estimates for stratospheric release of 20–40% of total emis- sions .

In this project we assume that 30% of the emissions in cruising are released in the troposphere for both intra European and intercontinental flights.

Furthermore, we assume that airports are situated in at the periphery of cities and hence the emissions due to landing and take off are characterized as emissions in low population area. The assumptions made for the calculation and the resulting figures of the share of LTO are presented in Table 7-7.

Table 7-7: Share of fuel consumption of LTO

Distance [km] 1) LTO [kg/LTO] 1) Cruise [kg/km] 1) Cruise total [kg] LTO [%] Cruise [%] Intra Europe 500 730 2 1050 41.01 58.99

Intercontinental Long Haul 6000 3100 11 66000 4.49 95.51

Average Freight Transport (5.4% EU, 94.6% INT)

5725 2982 10.55 60399 4.70 95.30

Average Passenger Transport (29.9% EU, 70.1% INT)

4157 2389 8.3 34507 6.47 93.53

1: figures are derived from Dings et al. (2002). For intra Europe aircraft movements we employed the distance of an average short haul flight in Europe.

The remaining emission in the upper troposphere are characterised as emissions to air, unspecified