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1998 Fuel Use and Emissions for Danish IFR Flights

3. Current CORINAIR aircraft emission estimates

The previous version of the detailed CORINAIR methodology (CORINAIR, 1996) is currently used to compute the annual Danish aircraft emissions (Winther, 1999b). Model estimates for 1994 and onwards is a part of the official Danish emission figures reported to international conventions.

To operate the methodology initial information must be provided on the number of domestic and international LTOs per aircraft type and their respective LTO times-in-modes. From these the LTO fuel consumption and emission factors can be calculated together with the total LTO energy use and emissions. The cruise energy use is estimated as the difference between the total fuel use from aviation fuel sale statistics and the total calculated LTO fuel use. At last when given the fuel related cruise emission factors the total domestic and international energy use and emissions can be calculated.

3.1 Air traffic statistics

As a start the methodology needs information on the number of LTO’s grouped by representative aircraft types at all airports, local LTO times-in-mode and most frequently used engine per aircraft type.

At the most detailed estimation level all individual aircraft with their specific engines should be represented in the emission inventory and data on their actual LTO times-in-mode should be available in every airport. This detailed knowledge is very hard to obtain and therefore data must be used on a more aggregated level for practical calculations. Assumptions must be made further to account for missing data in some situations.

For Denmark air traffic statistics exist on different levels with data gaps in some areas, too. The air traffic activity in Denmark takes place mainly at Copenhagen Airport. With more than 100,000 LTOs per year this airport is a large emission point source in CORINAIR. From a national point of view the air traffic statistics for Copenhagen Airport are well described both as regards the number of LTOs per aircraft type and the LTO times-in-mode. The available statistics from the provincial airports are more scarce; they only submit rough information on the number of LTOs in traffic categories. Therefore, in order to carry out the emissions calculations properly it is necessary to make some assumptions.

In spite of the different levels of Danish aviation statistics it is possible to divide the air traffic activity into the number of LTOs per aircraft type by using different statistical sources. In the LTO groupings, see table 3.2, no distinction is made between charter and scheduled air traffic (large aircraft) and small aircraft are treated separately. Moreover, Copenhagen Airport is parted from the provincial airports in the inventory due to CORINAIR emission source definitions and the varying statistic levels in general.

Figure 3.1
Route map¹ for the CORINAIR aircraft calculation methodology (CORINAIR, 1996)
¹ EF: Emission factor

3.2 Copenhagen Airport

To a large extent the CORINAIR emission inventory of Copenhagen Airport is based on an EIA (Environmental Impact Assessment), see Copenhagen Airport (1996). In this work all aircraft types operating at Copenhagen airport are grouped into 20 different representative aircraft types (large aircraft). The most frequently used engine type is also found for each of these. At the same time their respective LTO times-in-modes have been measured.

Table 3.1
LTO modal time intervals measured at Copenhagen Airport

No information is available to distinguish between domestic and international LTOs per aircraft type at Copenhagen Airport. In the airport’s own air traffic statistics (Copenhagen Airport, 1999) the annual number of LTOs are given for all aircraft types regardless of destination. In the Danish CORINAIR inventory these numbers are grouped into LTO numbers for the representative aircraft types established in the EIA. Furthermore, these LTOs are assumed to be international.

Another source of information, Statistics Denmark (1999), lists the number of domestic and international LTOs (large aircraft) and small aircraft (general aviation) in each Danish airport. From Statistics Denmark (1999) and Copenhagen Airport (1999) it is finally possible to find more accurate numbers of international LTOs per aircraft type and domestic LTO totals at Copenhagen Airport. The assumption that all LTOs by large aircraft reported at Copenhagen Airport (1999) are international is expected to give to many international LTOs, compared with the real LTO number in Statistics Denmark (1999). The difference in LTO numbers is subtracted from the representative aircraft type Fokker F50 LTOs and added to domestic LTOs, which are represented by the same aircraft.

3.3 Provincial airports

Since no LTO data for provincial airports are given in Statistics Denmark (1999) for individual aircraft types, all domestic and international LTO’s (for large aircraft) are assumed to be carried out by a Fokker F50. Furthermore, an overall assumption in the Danish inventory is that all domestic traffic with large aircraft takes place between Copenhagen and the provincial airports. The engine type and specific LTO timings are shown in table 3.1. The taxi-in and out time intervals are small in the Danish provincial airports and are set to 2.5 mins in the inventory, respectively.

Table 3.2
Number of take offs in Danish airports

3.4 Fuel consumption and emission factors

The engine power settings and time duration of the different parts of a LTO cycle is defined by the International Civil Aviation Organisation (ICAO), see (ICAO, 1993). For engine emission certification purposes modal measurements of the CO, VOC and NO_x emissions and the fuel consumption are made during the test cycle for all engine types fitted to large aircraft.

Table 3.3
The times-in-modes and power setting for the ICAO LTO-cycle

The engine emission and fuel consumption data can be found in ICAO (1995) or at http://www.dera.gov.uk. The emission indices (EI) are given as g emission kg fuel^-1 and the fuel consumption rate as kg fuel s^-1 for each LTO mode. The ICAO LTO times-in-modes differ from the Danish time intervals in table 3.1. To calculate the Danish LTO fuel consumption and emission factors the ICAO emission indices and fuel consumption rates are combined with the Danish LTO times-in-modes using the following equation:

(1)

Where t_m is the time in LTO-mode m and EI_m and ff_m the corresponding emission indices and fuel flows, respectively. For CO₂ the LTO emission factors are calculated as LTO fuel use multiplied with the lower heating value (43.5 MJ/kg) and the fuel related CO₂ emission factor (72 g CO₂/MJ). The SO₂ emission factors are derived from the fuel use factors by using a weight percent of 0.01% sulphur in the fuel. The atom weight of S equals the weight of O₂ thus giving a mass ratio of 0.02% SO₂ per unit of fuel used.

Table 3.4
LTO fuel use and emission factors

Fuel-based cruise emission factors are taken from CORINAIR (1996) as a single set for large aircraft. Small aircraft do not have to meet any emission standards. Therefore, no emission factors are available from approved emission measurement procedures. Instead emission factors are estimated by using the fuel related emission factors for non-catalytic cars. In addition all flying with small aircraft are assumed to take place below 3000 ft.

Table 3.5
Cruise fuel use and emission factors

3.5 Calculation of energy use and emissions

The energy use by large aircraft is calculated for both domestic and international LTOs by multiplying the LTO fuel consumption factor for each aircraft type with the corresponding number of LTOs.

The next step is to calculate the total cruise energy use by domestic and international flights as the difference between the total jet petrol sales in Denmark (DEA, 1999) and the total calculated LTO fuel use for domestic and international air traffic, respectively. No further distribution of cruise fuel use into aircraft types is made. Such an allocation has no physical meaning since only one set of cruise emission factors are available in the detailed calculation methodology.

In order to calculate the domestic and international LTO emissions, the number of LTOs for each aircraft type is multiplied with the respective emissions per LTO. The cruise emissions are estimated as the domestic and international cruise fuel use times their fuel related cruise emission factors. For small aircraft the fuel use is taken from domestic and international aviation gasoline sales statistics. The domestic and international emissions are calculated by multiplying the aviation gasoline fuel amount with the single set of fuel related LTO emission factors.

There is a need to improve some parts of the current model version. If aggregated emission factors for cruise and emission factors for LTO in provincial airports can be derived from a number of representative aircraft, more precise emission estimates are expected.

Table 3.6  Look here!
The Danish 1998 CORINAIR aircraft emission inventory

3.6 Aviation fuel statistics for Denmark, OECD and globally

The most recent year with aviation fuel statistics available for Denmark, OECD and globally is 1997. The total fuel sold in airports in the Kingdom of Denmark reflects the part of air traffic movements taking place. Some important factors that determine the number of flights are size of population, geographical situation, and economic growth and prosperity. This fuel sale number in 1997 account for a little more than 0.4% of the global fuel sale figure, almost 0.6% of the OECD total and around 2.2% of all fuel sold in airports in the EU. Due to definitions some differences occur between the International Energy Agency (IEA) and the Danish Energy Agency (DEA) aviation fuel statistics.

In IEA statistics (1999a and b) the fuel used by flights within Denmark and flights from Greenland and the Faroe islands bound for Denmark are included under domestic aviation. The domestic total is 117 kilotons of fuel and the number also include military fuel use. Domestic flights within Denmark use 55 kilotons of jet fuel, while the fuel used by flights from Greenland or the Faroe islands bound for Denmark use 62 kilotons of fuel. The latter fuel use number is based on the fuel sale from Danish Refineries to the airports in Greenland and the Faroe islands. The international fuel total is 675 kilotons and include the fuel used by all flights from Denmark and bound for Greenland, the Faroe Islands and other international countries.

The DEA statistics (1998) cover the domestic fuel used by all flights within Denmark (55 ktonnes). This number also includes the fuel used by military flights. The fuel used by flights from Denmark to Greenland, the Faroe islands and other international countries are reported as international fuel use. The fuel used by flights from Greenland or the Faroe islands and bound for Denmark is not included in the statistics.

Table 3.7
Aviation fuel sale figures for Denmark, OECD and globally