Aircraft engine environmental standards

The engine Oxides of Nitrogen (NO_x) 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 NO_x goals need to be updated for them to remain relevant and consideration should be given to the potential to set goals for nvPM emissions.

NO_X emissions

The NO_x 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)

NO_X performance of new aircraft engine deliveries

illustrates the trend over time of aircraft joining the European fleet and their performance against the various ICAO engine NO_X 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 NO_X standard from 1 January 2020 onwards, thereby suggesting a need to review this standard within the CAEP/14 work programme (2025-2028).

nvPM emissions

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.

Modelling of non-CO₂ emissions in cruise

The CAEP/13 work programme (2022-2025) has evaluated the relationship between NO_x emissions measured in the reference Annex 16 Volume II certification Landing and Take-Off (LTO) cycle and NO_x emissions in cruise. A new cruise NO_x 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 NO_x 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 5^th 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]

⁴ ICAO Annex 16 Volume II contains international aircraft engine emissions standards. NO_x limits are defined as the mass (Dp) of NO_x emitted during the Landing and Take-Off (LTO) test cycle and divided by the rated thrust of the engine (Foo), expressed in grams of NO_x per kiloNewton of thrust (g/kN).
⁵ NO_x limits are defined as the mass (Dp) of NO_x 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.

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