Aircraft engine environmental standards

 

The engine Oxides of Nitrogen (NOx) and non-volatile Particulate Matter (nvPM) standards,4 alongside the aircraft noise and CO2 standards, define the design space for products to simultaneously address noise, air quality and climate change issues.

 and   highlight in red boxes the limited developments in certified aircraft engine types since the last report with the Trent 7000 performance improvement package and the new Pearl 700 and PW812 engines 
[9]
. As per the aircraft level environmental standard, the ICAO Independent Experts Panel NOx goals need to be updated for them to remain relevant and consideration should be given to the potential to set goals for nvPM emissions.

The NOx standards5 for aircraft engines have become more stringent between 1996 and 2014, and are typically referred to by the CAEP meeting in which they were agreed (CAEP/2, CAEP/4, CAEP/6 and CAEP/8)

 illustrates the trend over time of aircraft joining the European fleet and their performance against the various ICAO engine NOX emissions standards. It highlights that all new aircraft engine deliveries were compliant with at least CAEP/6 by 1 January 2012, thereby meeting the CAEP/6 production cut-off date of 1 January 2013. In addition, all new aircraft engine deliveries have met the latest CAEP/8 NOX standard from 1 January 2020 onwards, thereby suggesting a need to review this standard within the CAEP/14 work programme (2025-2028).

The latest certified aircraft engine nvPM mass and number emissions data is provided in 

 and  , and are grouped based on combustor technologies. The Y axis of those figures uses a logarithmic scale to differentiate between combustor types more easily.

The CAEP/13 work programme (2022-2025) has evaluated the relationship between NOx emissions measured in the reference Annex 16 Volume II certification Landing and Take-Off (LTO) cycle and NOx emissions in cruise. A new cruise NOx Metric System based on LTO data and Annex 16 Volume III fuel burn data is being considered with the aim of improving the modelling of cruise NOx emissions for lean burn engines within the Boeing Fuel Flow Method (BFFM) and the assessment of the effect of non-CO2 emissions on climate change 

[10]

In addition, a proposed 5th LTO reporting point for nvPM emissions at a cruise thrust setting (57.5% of maximum sea level static thrust) is proposed to be included in the ICAO Annex 16 Volume II certification requirements to enhance the understanding of engine nvPM emissions and improve cruise nvPM modelling, e.g. within the Mission Emissions Estimation Methodology (MEEM) 

[11]
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4 ICAO Annex 16 Volume II contains international aircraft engine emissions standards. NOx limits are defined as the mass (Dp) of NOx emitted during the Landing and Take-Off (LTO) test cycle and divided by the rated thrust of the engine (Foo), expressed in grams of NOx per kiloNewton of thrust (g/kN).
5 NOx limits are defined as the mass (Dp) of NOx emitted during the Landing and Take-Off (LTO) test cycle and divided by the thrust of the engine (Foo). The limit also depends on the overall pressure ratio of the engine.