This project has received funding from the Clean Sky 2 Joint Undertaking under the European Union’s Horizon 2020 research program under grant agreement No 863969
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This document captures proceedings from a workshop on the health impacts of ultrafine particles held on 15 September 2020, under the Aviator, Raptor, and Tube projects.
To address the known Local Air Quality impacts of ultrafine combustion derived soot, the International Civil Aviation Organisation (ICAO) have recently adopted a non-volatile Particulate Matter (nvPM) regulation in addition to those of NOx, UHC’s and CO for civil aviation gas turbines. Increased water humidity is known to reduce the formation of NOx in flames through localised temperature reduction, however its impact on emitted nvPM is to date not clearly understood. To address this knowledge gap, nvPM formation mechanisms were assessed empirically at increasing water loadings both at atmospheric pressure – in a RQL representative optical combustor fuelled with Jet A and alternative fuel blends – and during a full-scale Rolls-Royce aero-derivative Gas Turbine test fuelled on Diesel. In line with previous studies, in the RQL combustor rig it was observed that increased hydrogen content in the test fuel – associated with a 100% Gas-To-Liquid (GTL) derived aviation kerosene with low aromatic content (0.05%) – reduced nvPM number concentrations by an order of magnitude compared to a baseline Jet A-1 fuel with representative aromatic content (24.24%). For all fuels tested it was also observed that an elevated water loading in the primary combustion zone (≤ 0.05 kg /kg of dry air), representative of maximum global humidity levels, resulted in reductions of both nvPM number and mass concentrations of 40% and 60% respectively. During a full-scale Rolls-Royce gas turbine study similar trends were observed, with an 85% reduction in measured nvPM mass whilst water was injected into the combustor at flow rates 25% higher than the diesel fuel flow. The nvPM reductions in both experiments are significantly larger than can be explained by water dilution effects alone, with less impact noted for fuels with higher hydrogen content. This suggests the reduction may be in part due to chemistry. Preliminary chemical kinetic investigations were undertaken using CHEMKIN-PRO and suggest that the soot reduction mechanism is potentially via a reduction in PAH formation within the flame zone. However, further analysis is required to validate if this mechanism is dominated by in-flame OH reduction mechanisms or influenced significantly by other factors associated with water dilution and reduced flame temperatures.
Aircraft gas turbine engines produce ultrafine PM which has been linked to local-air-quality and environmental concerns. Regulatory sampling and measurement standards were recently introduced by ICAO to mitigate these emission of nonvolatile PM (nvPM). Currently, reported nvPM emissions can significantly under-represent engine exit concentrations due to particle loss. A System-Loss-Tool (SLT) has been proposed to correct for particle loss in the standard sampling and measurement system permitting an estimation of engine exit concentrations for airport environment inventories. Thermophoretic and bend particle loss mechanisms are predicted in the SLT using expressions derived from the literature, which are not in all cases empirically validated to conditions representative of aircraft nvPM exhaust sampling methodologies. In this study, thermophoretic (Tgas≤910 °C) and coiling-induced (≤3960°) particle loss were measured using sampling variables relevant to aerospace certification. Experiments were performed using laboratory generated solid particles (fractal graphite, cubical salt and spherical silica) bounding the upper and lower limits of aircraft soot morphology (i.e., particle effective density, mass-mobility exponent, primary-particle-size). These were aerodynamically classified using a Cambustion Aerodynamic-Aerosol-Classifier (AAC) at electrical-mobility diameters ranging from 30 to 140 nm. The AAC was shown to efficiently classify salt and silica particles, producing monomodal distributions ≥25 nm electrical-mobility GMD, whilst classifying fractal graphite >40 nm electrical-mobility GMD (calculated as da≥20 nm) albeit generally displaying larger GSD’s. Thermophoretic loss at ΔTgas of 0–880 K correlated well with the SLT for non-fractal particles with losses ≤39.2% measured, with higher depositions observed for graphite (4.1%) considered insignificant compared to overall measurement uncertainty. Coiling a 25 m sample line in compliance with ICAO standards induced negligible additional particle loss at flowrates relevant of aircraft exhaust sampling, in agreement with SLT-predicted bend losses. However, additional losses were witnessed at lower flowrates (≤13% at 30 nm), attributed to secondary flow diffusion loss induced by the coiling.
D3.3. Identification of Knowledge Gaps and Research Needs
D4.1. CAEP 11 Uncertainty Assessment
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