the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 28 Feb 2024
Measurement report: In-flight and ground-based measurements of nitrogen oxide emissions from latest generation jet engines and 100% sustainable aviation fuel
Abstract. Nitrogen oxides, emitted from air traffic, are of concern due to their impact on climate by changing atmospheric ozone and methane levels. Using the DLR research aircraft Falcon, total reactive nitrogen (NOy) measurements were carried out at high altitudes to characterize emissions in the fresh aircraft exhaust from the latest generation Rolls-Royce Trent XWB-84 engine aboard the long-range Airbus A350-941 aircraft. The impact of different engine thrust settings, monitored in terms of combustor inlet temperature, pressure, and engine fuel flow, was tested for two different fuel types: Jet A-1 and for the first time a 100 % sustainable aviation fuel (SAF) under similar atmospheric conditions. During ground emission measurements, a range of combustor temperatures and an additional blended SAF were tested. We confirm that the NOx emission index increases with increasing combustion temperature, pressure and fuel flow. We find that as expected, the fuel type has no measurable effect on the NOx emission index. These measurements are used to compare to cruise NOx emission index estimates from three engine emission models. Our measurements thus help to understand the ground to cruise correlation of current emission models while serving as input for climate modelling, and extending the extremely sparse data set on in-flight aircraft NOx emissions to newer engine generations.
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RC1: 'Comment on egusphere-2024-454', Anonymous Referee #1, 03 Apr 2024
Even though the findings are not of great surprise, this manuscript is an important contribution and a verification of established concepts. it should be published. Here are some specific comments to make it more comparable with other studies:
- A clarification is needed what is measured and reported in the specific sections and plots. From my understanding for all altitude measurements NOy is measured and reported for all ground level measurements NOx is reported. Since NOx ≠ NOy even at the engine exit (HONO can make up 6% fraction e.g. dx.doi.org/10.1021/es200921t) the actual reported data needs to be better described (or not labeled as NOx) throughout the manuscript. Maybe I misunderstood, but also then it needs a clarification.
- Table1: Please add energy content, aromatic content, and density of fuels
The information on the used fuel is rather sparse – while they energy content might not vary much probably around 42- 43 MJ/kg it might provide a better insight why not much difference was observed between the fuels? The other parameters are needed to link the information provided to other studies and the ICAO database – this is really needed for putting the results into context, the study has otherwise only a limited value. - Figure 3 are the blue points from EDB or your measurements? Please clarify
- Figure 6. How do these data compare to the ICAO EDB? Are any of the ICAO Annex16 corrections applied to the data or is this raw? Please clarify.
Citation: https://doi.org/10.5194/egusphere-2024-454-RC1 -
RC2: 'Comment on egusphere-2024-454', Anonymous Referee #2, 22 Apr 2024
This measurement report focuses on aviation NOx emissions, which are an important component of aviation’s climate and air quality impacts. It presents results from an extensive set of hard-to-perform experiments, covering a) both in-flight and ground observations and b) multiple fuel types. I have the following suggestions which would in my opinion strengthen the paper towards publication:
- The paper is at times hard to follow. The authors could clarify a bit better throughout what exactly is being shown or discussed. For example, in Figure 5, are the model results obtained using data from the ground tests?
- The fact that the paper contains both in-flight and ground measurements is in my opinion one of its strongest points, and the authors could further build on that. For example, adding an equivalent to Figure 1 for the ground tests would be helpful, and expanding the description of what exactly was measured on the ground, how, at what distance, and how many times.
- Section 3.4: why is this analysis not performed for the ground measurements (or if it is please clarify)?
- Putting the results in the context of ICAO’s Aircraft Engine Emissions Databank would make this work more impactful (e.g. a comparison or equivalent that preserves any sensitive data).
Minor comments:
- Some typos: line 253, Table 2 T2 unit, x-axis of Figure 6?, x-axis of Figure 8?
- It would be helpful to add to Table 1 the number of observations for each case (i.e. how many of the “points” that appear in following plots, e.g. Figure 4, are from each), separating the ground from the in-flight measurements for the ECLIF3-2 case.
- The data repo would benefit from a README or equivalent file. Despite the individual files having headers, an overview of the data provided would be helpful. For example, does it only include the in-flight measurements?
Citation: https://doi.org/10.5194/egusphere-2024-454-RC2
Data sets
CO2 and NOy aircraft measurement data obtained within the framework of the ECLIF3 campaign Theresa Harlass et al. https://doi.org/10.5281/zenodo.10646359
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