Findings of the Validation of
the Advanced Emission Model (AEMIII) version 1.5
Safety, Analysis and Scientific Centre of Expertise
for Society, Environment & Economy Research Area (SEE)
Validation
a key issue for emission estimation
AEMIII validation results for fuel burn and proportional
pollutants
Fuel flow
discrepancies compared to ICAO engine data
Validation a key issue for emission
estimation
The importance of global emission and local air quality analysis tools in support of the political decision making process is increasing with increasing public interest in the environmental impact of aviation.
Since the decisions taken can have significant economic consequences on all aviation stakeholders, e.g. airlines, airports, air traffic service providers etc. it is crucial to ensure that the information provided to the political decision making process is reliable.
This requires careful verification and validation of all tools used in this context.
A key factor for such a validation process is the availability of operational airline data detailing precise flight profile and fuel burn information. As the airlines would be the first to feel the potential consequences of changes in the aviation system motivated by environmental issues, such as fuel taxes, environmental route charges, emission landing fees etc., it is in their interest to ensure that emissions are estimated accurately. Nonetheless it is extremely difficult to obtain operational data from airlines.
The situation for emissions is even more complex. Emission information for given aircraft and engine combinations is not available to the research community. Test bed information from the engine certification process is only available for ground level. Statistically, the number of tests per engine is not sufficient. The effect of the engine installed in a particular airframe and changes in emission indices as a function of aircraft attitude, altitude, Mach number, weight etc. are not explicitly available in the ICAO Engine Exhaust Emission Databank.
As a consequence, for tools used in the past, only rough error estimates have been possible. Error margins of 30% and more for fuel burn and emissions have been reported even in the context of European environmental reference projects such as ANCAT/EC1 & EC2, MeeT, etc.
AEMIII validation results for fuel
burn and proportional pollutants
Fuel burn and emission estimations of AEMIII in its version 1.5 have been validated against Flight Data Recordings (FDR) of more than 3850 operational missions and more than 3800 Operational Flight plans extracted from SITA messages.
The AEMIII results are extremely realistic and exceed the expectations at the start of the project. The error for fuel burn and directly proportional emissions for complete missions is only about 1 %.
This extremely positive result of AEMIII v1.5, lies well within the 10% acceptance limit defined by ICAO/CAEP6.IP5.
The results for all 3850 missions for which flight data recordings were available are shown in the figure below.
Figure 1: The AEMIII fuel burn
vs. operational fuel burn of 3850 FDRs
The quality of the fuel burn estimates is clearly related to the AEMIII
design decision to use fuel flows from the EUROCONTROL Base for Aircraft
Data (BADA) above 3000 feet. These fuel flows are available as a function
of attitude and altitude, and take into account possible engine/airframe installation
effects.
Fuel flow
discrepancies compared to ICAO engine data
The validation of AEMIII also highlights significant differences between
real fuel flows and those documented in the ICAO
Engine Exhaust Emissions Databank. This is true both for high and low thrust
fuel flows. The figure below compares ICAO fuel flow limits against those of
BADA and those found in the FDR data for the Airbus 319. Findings for all other
aircraft types available in the FDR data are similar to those for the A319.
Figure 2: Fuel flow limits – A319
The problem of unrealistic low and high thrust fuel flows is a
fundamental issue which requires further discussion with domain experts, since
this leads to systematically incorrect fuel burn and emission estimates for any
project relying on the ICAO fuel flows.
Increased HC
and CO emissions
The NASA Scheduled Civil Aircraft Emission Inventories for 1992 [Ref 1] based on ICAO fuel flows indicates that the internal distribution between Oxides of Nitrogen (NOx), Carbon Monoxide (CO) and Hydrocarbon (HC) should vary between 72.5 and 90% for NOx, 25 and < 10% for CO and <1 - 2.5% for HC, dependent on the mission length. These percentages are based on Boeing standard mission profiles, for a mission range between 750 and 5500 km (400 NM and 3000 NM) for a B757-200.
Figure 3: Emissions Comparison
of 757-200 for a 750 km and 5500 km
Based on the more realistic fuel flow assumptions extracted from BADA for 3800 flights with several aircraft types the share of the three pollutants differs significantly from the NASA findings. The share of oxides of Nitrogen varies between only 42 – 68%. CO emissions rise to 28 – 49% with HC emissions rising at the same time to 3 – 9%. The variation depends on mission length etc.
Figure 4: Comparison of emissions produced by AEMIII with SITA data
Conclusions
If these findings are confirmed in future work it would be necessary to conclude that the information available in past aviation emission inventories significantly underestimates CO and HC emissions. Hydrocarbon emissions are of growing importance in the context of Local Air Quality in the neighbourhood of airports.
As a result of this validation exercise it can be concluded that the fundamental approach implemented within AEMIII v1.5 is leading to results with a very high level of realism. Fuel burn calculations, based on BADA fuel flows are very close to real values. Consequently, the same can be concluded for the fuel burn proportional pollutants, e.g. H2O, sulphur oxides SOx and CO2.
NOx results align with earlier estimates by domain experts and are based on a variation of the widely recognised and accepted BM2 method, BM2-EEC.
Similarly, the
estimation approach for
The AEMIII VOC/TOG estimation approach follows a method developed and published by U.S. EPA and which is based on the estimations for HC.
See the full AEMIII v1.5 validation report and its appendices, which include detailed results and descriptions of the above methods.
Future Work
Additional validation against FDR data from more airlines covering additional aircraft types is envisaged. This will depend mainly on the airlines’ readiness to support such validation activity with operational data.
AEMIII v1.5 will be distributed to a short list of domain experts for review and to capture comments which are expected to lead to further improvements. The improved version of AEMIII will be made available to the entire aviation emissions and atmospheric research community on a commerical low license fee basis.
In parallel AEMIII will be implemented within the EUROCONTROL data warehouse project PRISME. Under the working title PAGODA Phase2 it will enable nightly estimation of fuel burn and emissions for the previous day for the entire ECAC area. Dependent on several technical and political factors it is hoped that the information obtained in this way by AEMIII will support European (EC) and International (EMEP) reporting requirements on aviation emissions in a more precise way than in the past, where this information was simply extrapolated from available bunker fuel information.
For further information about global emissions please contact Frank Jelinek.
For further information about the Society, Environment, Economy research area please contact Ted Elliff.
[Ref 1]
Scheduled
Civil Aircraft Emission Inventories for 1992: Database Development and
Analysis; April 1996; NASA LRC; Contractor Report 4700; Steven L. Baughcum, Terrance G. Tritz, Stephen C. Henderson,
David C. Picket)