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Towards improved correction methodology for regulatory aircraft engine nvPM measurement

Durand, Eliot 2019. Towards improved correction methodology for regulatory aircraft engine nvPM measurement. PhD Thesis, Cardiff University.
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Abstract

Local air quality and environmental concerns over particulate matter (PM) emissions have recently been exposed. Aircraft gas turbine engines produce ultrafine PM (<100 nm), which is believed to be particularly harmful due to their small size. Regulatory sampling and measurement systems have been introduced by ICAO to mitigate the emission of non-volatile PM (nvPM). Whilst this is a significant development, still several sources of measurement and correction uncertainty exist. An SAE-31 system loss tool (SLT) has recently been proposed to predict system loss correction factors in order to predict engine exit plane concentrations from the regulatory measurements. However, the SLT requires several assumptions which lead to unknown levels of uncertainty. The aim of this thesis is to reduce the uncertainty associated with predictions of engine exit plane nvPM mass and number concentrations. Various methods for aerosol generation were proposed and characterised, leading to the selection of an optimised system for the laboratory particle loss experimentation. Silica, salt and graphite were found to provide a suitable range of morphological and physical particle characteristics. Theoretical models proposed for particle loss mechanisms comprising thermophoresis, diffusion and ‘bend loss’ theory, typically found within an ICAO compliant sampling system, have been validated experimentally at conditions representative of aircraft exhaust sampling. The impact of particle morphology on transport through the main sections of the sampling system has been established. The current ICAO compliant sampling and measurement system was deployed across a range of Rolls-Royce engine types and conditions, covering the entire thrust range. This provided a broad range of PM data - with average particle effective densities ranging between 0.3-0.8 g/cm3 derived - from which new correlations have been proposed. Uncertainties associated with the regulatory nvPM sampling and measurement methodology have been independently evaluated; they are estimated to be 66% for EInumber and 25% for EImass for the smallest particles (10 nm). Preliminary studies have highlighted additional uncertainties associated with line shedding, ambient effects and fuel properties, which are not currently included within regulation. Theory predicts that losses <90% (for number) occur in a compliant sampling system with only thermophoresis currently corrected in reported EI’s. System loss correction has the potential to predict engine exit plane concentrations using measured EInumber and EImass by correcting for particle loss. Current SLT assumptions regarding lognormality, GSD and particle density were empirically validated and found to generate associated uncertainties of 76% and 27% for the predicted number and mass system loss correction factors respectively. It is demonstrated that an additional particle size measurement improves the estimation of engine exit plane concentrations by removing the requirement for assumptions, hence significantly reducing overall uncertainty.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: Particulate Matter; Aviation emissions; Particle transport; Particle loss; Particle generation; Alternative fuels.
Date of First Compliant Deposit: 31 October 2019
Last Modified: 31 Oct 2019 09:47
URI: http://orca-mwe.cf.ac.uk/id/eprint/126400

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