Concerns surrounding the impact of harmful emissions from aircraft are driving increased adoption of Sustainable Aviation Fuel (SAF) by the aviation industry. In addition to reducing lifecycle CO2 emissions, significant reductions in non-volatile Particulate Matter (nvPM) emissions are achievable for SAF compared to conventional aviation fuels, which have previously been observed to correlate with higher Fuel Hydrogen Content (FHC). However, relative reductions in nvPM for higher FHC fuels are not consistent across all engine power conditions, with the largest benefits observed at lower power conditions. To better understand the fundamental mechanisms affecting nvPM formation in gas turbine engines operating with different fuels, it is important to isolate and determine the contribution of additional parameters alongside FHC on rates of nvPM emissions. Towards this, the present study explores the influence of fuel atomisation quality on nvPM formation rates. The emissions produced by the combustion of several aviation fuels (including conventional Jet A-1, SAF, and SAF/Jet A-1 blends) in a small-scale Rich-Quench-Lean (RQL) research combustor were characterised using a regulatory nvPM sampling and measurement system. A design feature of the combustor allowed atomisation quality to be varied independently of primary (rich) zone equivalence ratio, with reduced atomisation quality resulting in consistently higher nvPM emissions. Measured nvPM EImass and EInumber showed some evidence of a fuel dependency, whereby emissions from higher FHC fuels appeared to be less affected by atomisation changes. Sauter Mean Diameters (SMD) were estimated for the fuel sprays produced during emissions measurements using an atomiser-specific empirical correlation, derived from independent laser-based spray benchmarking experiments conducted at ambient conditions. Using this correlation, it was predicted that small increases in SMD of 3-4 mu m (similar to 5-6%) resulted in nvPM increases of up to 108% EImass and 87% EInumber.

Particulate matter (PM) emitted by aircraft engines represents a major non-CO2 emission source, primarily composed of soot particles generated by incomplete fuel combustion. These particles act as ice nuclei in contrail formation and degrade air quality near airports. A novel technique is introduced to investigate aircraft engine PM emissions using a short-range elastic backscattering lidar. This approach was validated through trials conducted at the Airbus Bikini test site using the compact and field-deployable Colibri Aerosol Lidar (CAL) sensor. This instrument enables rapid, non-invasive, and remote measurement of volume backscatter profiles, which can be converted into PM mass and number concentrations without the need to sample particles from the aircraft exhaust. Our findings demonstrate the feasibility and potential of using a short-range elastic backscattering lidar for remote assessment of aircraft PM emissions across various engine thrust levels.

Despite recent advancements in regulatory standards for aircraft turbine engines, significant uncertainty remains in accurately quantifying non-volatile particulate matter (nvPM) number and mass emissions due to the complexity of sampling, measurement, and calibration procedures. The transition to new engine technologies and sustainable aviation fuels can also reduce regulatory nvPM levels towards the limit of quantification (LOQ), necessitating better quantification and mitigation of these uncertainties. This study, initiated by the European Union Aviation Safety Agency (EASA) and funded under the EU Horizon 2020 RAPTOR and SAMPLE IV research programmes, investigated uncertainties in instrument drift, system-to-system variability, nvPM mass LOQ, and system operability within current regulatory nvPM measurement, sampling, and calibration standards. To assess these uncertainties, two comparative tests of the European (EUR) and Swiss (CH) regulatory-compliant reference systems were performed over a twelve-month calibration cycle using a non-proprietary Rich-Quench-Lean (RQL) combustor rig, following prior parallel calibration of identical nvPM number and mass instrument technologies. Additional laboratory experiments using a range of aerosol sources were conducted to evaluate instrumentation and calibration uncertainty independently. With calibration and instrument-technology uncertainty minimised and enhanced cleanliness protocols applied, the nvPM Emission Index (EI) number showed <1 % systematic difference with 3 % variability between the EUR and CH systems, and the nvPM EI mass showed 3 % bias with 8 % variability. No annual instrument drift was observed in either the nvPM mass or number instruments. However, when directly comparing nvPM measurements across different calibration and instrument technologies, variability increased noticeably: Condensation Particle Counter (CPC) counting efficiency was impacted by particle type and morphology, even within the same CPC models, and a variability of 12 % (with biases up to 33 %) was observed across a range of nvPM mass instruments. In addition, particle shedding from the prescribed 1-mu m cyclone was observed during RQL combustor rig exhaust sampling and was found to significantly impact nvPM mass measurements at low concentrations, which are typical of modern engine technologies and sustainable aviation fuels. Yet, with improved cleanliness protocols, accurate nvPM mass quantification down to 3 mu g/m(3) was achieved. These findings provide critical insight into current regulatory practices and identify areas for improvement towards more accurate characterisation and future reduction of harmful nvPM emissions from aircraft engines.

Aircraft gas turbines engines produce ions through chemiionization thought to result in electrostatically charged engine exhaust emissions. Most combustion systems generate a symmetrical bipolar charge distribution. However, due to high temperatures and pressures in aviation combustors, associated fast residence times, and high post-flame temperatures, aircraft emissions have been predicted to exhibit an asymmetrical bipolar charge distribution. It is thought this asymmetry tends toward a positive polarity, resulting from an increase in post-flame thermal ionization. This study employed an Electrostatic Precipitator and a Scanning Mobility Particle Sizer to determine the charged fraction, and an electrometer to determine the mean charge per particle of aircraft emissions. Three aircraft engines were assessed across a number of powers for conventional and sustainable aviation fuels. In agreement with previous theoretical studies, the measured emissions were found to be charged, resulting in up to 58.1% of the emissions being charged, which correlated with engine power. The charge distribution of aircraft emission was observed to be asymmetrical, tending toward positive polarities at higher powers (combustor temperatures). Along with power, it was noted that particle size was a key parameter driving the charge. As such, a fuel dependence was found, whereby emissions produced by JetA-1 typically carried 11-17% more charge compared to SAF for similar conditions, which was attributed to the reduced particle sizes in SAF emissions. Differences in charge was observed between the different engines; however, variations in the respective emissions sampling systems may have contribute to the findings, resulting in uncertainties associated with dynamical unsteady charging.

Characterization of total particle emissions from an Airbus A350-900 during the ECLIF3 campaign is presented. Ground measurements ∼24.5 m behind the engine were conducted on three fuels: Jet A-1, HEFA-SPK, and a HEFA Jet A-1 mix. Data include number-mobility size distributions of total and nonvolatile PM (tPM and nvPM), nvPM mass, and size-resolved volatile PM (vPM) mass. LII analysis estimated primary particle size (dp) and specific surface area (SSA). At small sizes and low power, vPM number contributed up to 50% of tPM, with high-sulfur fuels producing the largest number of vPM and tPM. Fuels with higher hydrogen and lower aromatic content had smaller nvPM aggregate sizes (Dp) and lower mass, but larger dp, indicating more compact particles. SSA ranged from 160-200 m2/g, varied nonlinearly with thrust, and was lower for high-hydrogen fuels, potentially affecting toxicity. Combined data from this study and others revealed a strong inverse correlation between dp/Dp ratio vs Dp, relevant for ice nuclei (IN) modeling and climate impacts. vPM mass was dominated by lubrication oil, highly variable at low thrust, and wind-direction dependent; thus, even with Net Zero fuels (no sulfur, high hydrogen, no aromatics), engines may still emit IN via lubrication oil.

Volatile organic compounds, such as benzene, toluene, ethylbenzene and xylenes (BTEX) are emitted during the various aviation activities at ground level, such as take-off, approach and taxiing, that take place at or near airports. In addition to causing adverse health effects, these compounds are precursors of secondary aerosols (SOAs). The expected growth in air traffic in the near future makes it necessary to anticipate and control these emissions. As part of the AVIATOR project (EU Horizon2020), gaseous samples were collected in sorbent tubes and analysed by GC/MS, including emissions of commercial aircraft engines and airport ambient air, to study the evolution and transformation of BTEX. Three sites were selected: the INTA aircraft engine test cell, Ciudad Real and Madrid-Barajas airports. PM was collected on filters and substrates and analysed gravimetrically, with three different samplers: high-volume air sampler, Berner low pressure impactor, and an automated off-line sampler developed by CIEMAT. The ground idle configuration that simulates taxiing manoeuvres (before take-off and after landing) has been identified as a critical contributor to BTEX emissions at airports, with a concentration of over 460 ng L−1. Benzene is consistently emitted at higher levels than toluene and the emission of both increases with engine acceleration. In the plume, dilution with air decreases not only the concentration of BTEX, but also the prevalence of the compounds, making benzene no longer the dominant compound. Variations in diagnostic ratios and meteorological conditions, as well as sensitivity parameters to PM concentration, may suggest physicochemical transformation of BTEX into SOAs.

In recent efforts to reduce the radiative forcing of aviation, fuel design has gained increased attention. Sustainable Aviation Fuels are seeing wider adoption, and their positive impact on carbon dioxide and non-volatile soot particle emissions is well-established. However, the effects of the reduction in fuel sulfur content on volatile particle emissions and contrails are unknown. This study presents observations from in-flight measurements of emissions and contrails of an Airbus A350-900 burning fuels with different sulfur contents. We find a reduction in volatile particles and contrail ice crystals for low-sulfur fuels. For higher fuel sulfur contents, our findings demonstrate an additional contrail ice particle source through activation of sulfate aerosols. Our data-driven results need to be consolidated by in-flight observations with different fuels and engines. Eventually, climate impact estimates as well as regulations should account for the modulating effect of the fuel sulfur content on contrail ice particle numbers.

The optical properties of soot are crucial in estimating its climate impact through direct radiative forcing. Soot light absorption is typically quantified by the mass absorption cross-section (MACλ) or the absorption function E(mλ), which are wavelength dependent. Light absorbed by soot can be predicted from its MACλ using mass-concentration measurements, or from its E(mλ) using material density and an optical model accounting for soot-aggregate morphology. Recent work has shown that the soot MACλ shows a size dependency, due to a size-dependent degree of graphitization. We therefore hypothesized here that a similar size dependency may be observed for E(mλ), which we quantify here. To test this hypothesis, we present a novel approach to obtain size-resolved MACλ and E(mλ) of soot from a gas turbine engine by combining pulsed laser-induced incandescence signals with total mass-concentration measurements. E(mλ) was found to vary with soot-particle size, with values ranging between 0.23 to 0.31 for the smallest (≈ 0.13 fg) and largest (≈ 3 fg) particles measured. To our knowledge, these measurements are the first to demonstrate that E(mλ) not only varies between soot samples, but also within a population of soot particles, which impacts the interpretation of optical diagnostics and prediction of the radiative properties of soot.

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) in-flight 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 during the ECLIF3 (Emission and CLimate Impact of alternative Fuels 3) experiment. 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. In addition, a range of combustor temperatures and an additional blended SAF were tested during ground-based emission measurements. For the data measured during ECLIF3, 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 prediction methods. Our measurements thus help to understand the ground to cruise correlation of current engine emission prediction methods while serving as input for climate modelling and extending the extremely sparse data set on in-flight aircraft nitrogen oxide emissions to newer engine generations.

In order to reduce aviation's CO2 emissions and comply with current climate targets, the European Union plans a mandatory quota of 2 % sustainable aviation fuel (SAF) by 2025, rising up to >= 70 % SAF by 2050. In addition to a reduction of life cycle CO2 emissions, the use of SAF can also have a positive impact on particle emissions and contrail properties. In this study we present observations from the ECLIF3 (Emission and CLimate Impact of alternative Fuels) aircraft campaign, which investigated exhaust and contrail characteristics of an Airbus A350-941 equipped with Rolls-Royce Trent XWB-84 engines. For the first time, non-volatile and total particle emissions of 100 % HEFA-SPK (hydroprocessed esters and fatty acids-synthetic paraffinic kerosene) SAF, a blended fuel and a reference Jet A-1 fuel were measured in flight. A maximum reduction in non-volatile particle number emissions of similar to 41 % compared to the reference Jet A-1 fuel was measured at low cruise engine power settings when using 100 % HEFA-SPK. The reduction decreases to similar to 29 % for typical cruise engine settings and to similar to 22 % at high cruise engine power settings. The size of non-volatile particles was slightly smaller for HEFA-SPK compared to Jet A-1. We show a comprehensive analysis of the hydrogen content of globally available fuels. Our results demonstrate the impact of the fuel composition in terms of its aromatic, hydrogen, and sulfur content as well as of the effect of engine power settings on particle emissions. We demonstrate that the use of HEFA-SPK can significantly reduce particle emissions and thus contrail ice particles and therefore can provide an aviation climate benefit.

Carbonaceous particles, such as soot, make up a notable fraction of atmospheric particulate matter and contribute substantially to anthropogenic climate forcing, air pollution, and human health impacts. Thermal–optical analysis (TOA) is one of the most widespread methods used to speciate carbonaceous particles and divides total carbon (TC) into the operationally defined quantities of organic carbon (OC; carbon that has evolved during slow heating in an inert atmosphere) and elemental carbon (EC). While multiple studies have identified fundamental scientific reasons for uncertainty in distinguishing OC and EC, far fewer studies have reported on between-laboratory reproducibility. Moreover, existing reproducibility studies have focused on complex atmospheric samples. The real-time instruments used for regulatory measurements of the mass concentration of aircraft engine non-volatile particulate matter (nvPM) emissions are required to be calibrated to the mass of EC, as determined by TOA of the filter-sampled emissions of a diffusion flame combustion aerosol source (DFCAS). However, significant differences have been observed in the calibration factor for the same instrument based on EC content determined by different calibration laboratories. Here, we report on the reproducibility of TC, EC, and OC quantified using the same TOA protocol, instrument model (Model 5L, Sunset Laboratory), and software settings (auto-split-point: Calc405) across five different laboratories and instrument operators. Six unique data sets were obtained, with one laboratory operating two instruments. All samples were collected downstream of an aircraft engine after treatment with a catalytic stripper to remove volatile organics. Between-laboratory contributions made up a majority of the within-filter uncertainties for EC and TC, even for these relatively well-controlled samples. Overall, expanded (k = 2) uncertainties due to measurement reproducibility correspond to 17 %, 15 %, and 13 % of the nominal values for EC, OC, and TC, respectively, and 7.3 % in the EC / TC ratio. These values are lower than previous studies, including atmospheric samples without volatile organic removal; therefore, they likely represent lower limits for the uncertainties of the TOA method.

Aircraft gas turbine engines produce Particulate Matter (PM) emissions that have been linked to human health and climate issues, leading to the introduction of regulatory sampling and measurement standards for nonvolatile PM (nvPM) by the International Civil Aviation Organization (ICAO). Due to the significant nvPM losses within the prescribed sampling systems, loss corrections are used. Currently, based on sampling assumptions, electrostatic losses are not included in the standardized loss tool, as it is estimated to account for less than 3% of the total nvPM loss. This study experimentally investigated electrostatic loss of unipolar, bipolar, and naturally charged salt, silver, and carbon black particles at sizes (4-150 nm) and through sampling tubes representative of aircraft nvPM sampling. A unipolar and bipolar charger, along with a tandem SMPS-CPC measurement methodology, were employed to explore the impacts of tube material, Reynolds Number, tube diameter, residence time, and particle charge state on electrostatic loss. Minimal electrostatic loss was measured for conductive stainless steel and extensively bedded-in (above 300 h) carbon-loaded PTFE. However, an additional loss of up to 50% was observed within new cPTFE (with approximately 30 min of bedding-in), attributed to precipitation in an electric field. Furthermore, it was found that electrostatic dispersion could cause significant additional losses at high concentrations of unipolar or bipolar asymmetrically charged particles. Therefore, further research is required to determine the charge state of aircraft nvPM across different aircraft engine conditions to determine if unquantified electrostatic loss could occur within the probe section of the sampling system.

Concerns about civil aviation's air quality and environmental impacts have led to recent regulations on nonvolatile particulate matter (nvPM) mass and number emissions. Although these regulations do not mandate measuring particle size distribution (PSD), understanding PSDs is vital for assessing the environmental impacts of aviation nvPM. This study introduces a comprehensive data set detailing PSD characteristics of 42 engines across 19 turbofan types, ranging from unregulated small business jets to regulated large commercial aircraft. Emission tests were independently performed by using the European and Swiss reference nvPM sampling and measurement systems with parallel PSD measurements. The geometric mean diameter (GMD) at the engine exit strongly correlated with the nvPM number-to-mass ratio (N/M) and thrust, varying from 7 to 52 nm. The engine-exit geometric standard deviation ranged from 1.7 to 2.5 (mean of 2.05). The study proposes empirical correlations to predict GMD from N/M data of emissions-certified engines. These predictions are expected to be effective for conventional rich-burn engines and might be extended to novel combustor technologies if additional data become available. The findings support the refinement of emission models and help in assessing the aviation non-CO2 climate and air quality impacts.

The aviation sector, like most other sectors, is moving towards becoming net zero. In the medium to long term, this will mean an increase in the use of sustainable aviation fuels. Research exists on the impact of fuel composition on non-volatile particulate matter (nvPM) emissions. However, there is more sparsity when considering the impact on volatile particulate matter (vPM) emissions. Here, nine different fuels were tested using an open-source design combustor rig. An aerosol mass spectrometer (AMS) was used to examine the mass-loading and composition of vPM, with a simple linear regression algorithm used to compare relative mass spectrum similarity. The diaromatic, cycloalkane and aromatic contents of the fuels were observed to correlate with the measured total number concentration and nvPM mass concentrations, resulting in an inverse correlation with increasing hydrogen content. The impacts of fuel properties on other physical properties within the combustion process and how they might impact the particulate matter (PM) are considered for future research. Unlike previous studies, fuel had a very limited impact on the organic aerosol’s composition at the combustor exit measurement location. Using a novel combination of Positive Matrix Factorization (PMF) and high-resolution AMS analysis, new insight has been provided into the organic composition. Both the alkane organic aerosol (AlkOA) and quenched organic aerosol (QOA) factors contained CnH2n+1, CnH2n−1 and CnH2n ion series, implying alkanes and alkenes in both, and approximately 12% oxygenated species in the QOA factor. These results highlight the emerging differences in the vPM compositional data observed between combustor rigs and full engines.

To reduce the adverse impact of civil aviation on local air quality and human health, a new in-ternational standard for non-volatile Particulate Matter (nvPM) number and mass emissions was recently adopted. A system loss correction method, which accounts for the significant size-dependent particle loss, is also detailed to predict nvPM emissions representative of those at engine exit for emissions inventory purposes. As Particle-Size-Distribution (PSD) measurement is currently not prescribed, the existing loss correction method uses the nvPM number and mass measurements along with several assumptions to predict a PSD, resulting in significant uncertainty.Three new system loss correction methodologies using measured PSD were developed and compared with the existing regulatory method using certification-like nvPM data reported by the Swiss and European nvPM reference systems for thirty-two civil turbofan engines representative of the current fleet. Additionally, the PSD statistics of three sizing instruments typically used in these systems (SMPS, DMS500 and EEPS) were compared on a generic aero-engine combustor rig.General agreement between the three new PSD loss correction methods was observed, with both nvPM number-and mass-based system loss correction factors (kSL_num and kSL_mass) within +/- 10% reported across the engines tested. By comparison, the existing regulatory method was seen to underpredict kSL_num by up to 67% and overpredict kSL_mass by up to 49% when compared with the measured-PSD-based methods, typically driven by low nvPM mass concentrations and small particle size. In terms of the particle sizing instrument inter-comparison, an agreement of +/- 2 nm for the GMD and +/- 0.08 for the GSD was observed across a range of particle sizes on the combustor rig. However, it was seen that these differences can result in a 19% bias for kSL_num and 8% for kSL_mass for the measured-PSD-based methods, highlighting the need for further work to-wards the standardisation of PSD measurement for regulatory purposes.

In this paper, the characteristics of non-refractory aerosol using an International Civil Aviation Organization (ICAO) compliant sampling system emitted from two gas turbine relevant sources are reported, namely: an in-service turboshaft helicopter engine and a development combustor rig. Positive Matrix Factorisation (PMF) analysis was applied on an Aerosol Mass Spectrometer's (AMS) Unit Mass Resolution (UMR) organic aerosol (OA) data to identify three chemical factors: one unburnt fuel factor (AlkOA; Alkane Organic Aerosol) and two factors formed through oxidative processes: Semi Volatile Oxygenated Organic Aerosol (SV-OOA) and Quenched Organic Aerosol (QOA). The AlkOA factor's mass concentration correlated with Elemental Carbon (EC), an incomplete combustion tracer. The SV-OOA factor's mass concentration correlated with AMSdetected sulphate and Organic Carbon (OC) as characterised by a Sunset semi-continuous Analyser, with a high proportion of the OC converted to CO2 at lower temperatures (<= 475 degrees C) during the OC analysis, suggesting a higher volatility. The QOA factor's mass concentration corresponded with higher quantities of OC converted to CO2 at the highest temperature (870 degrees C) during the OCEC analysis protocol. The QOA factor comprised large quantities of AMS-detected organic mass concentrations (20-50%) for the IP Rig. In addition, issues were seen with the OCEC analyser, and future strategies for operation for sampling from aviation sources are considered. The work characterises the available chemical speciation present in the particulate matter phase within an ICAO compliant nvPM sampling system for in-service and development combustor rigs, and comparisons are made between mass spectra seen within this methodology and in evolved plumes.

Non-volatile Particulate Matter (nvPM) from aircraft gas turbine engines are harmful to both human health and the environment, but can be significantly reduced by using low aromatic Sustainable Aviation Fuel (SAF). As part of the Horizon 2020 funded JETSCREEN (JET fuel SCREENing and optimisation platform for alternative fuels) project, nvPM and gaseous emissions were characterised using regulatory compliant sampling and measurement methodologies for a small-scale (<250kW) non-proprietary RQL combustion rig, at pressures ranging from 1.0 to 2.4 bara. The impact of flow conditions, air to fuel ratio and fuel composition was investigated for a selection of conventional aviation Jet-A1 fuels, SAFs, and blended fuels. Measured concentrations were corrected for particle size-dependant system losses using particle size measurements, to be representative of combustor exit concentrations.Across the range of fuels (hydrogen contents 13.51%-15:31%), system-loss-corrected nvPM mass, number, and size were shown to decrease with increasing fuel hydrogen content, in agreement with previous studies. Inverse power law correlations are proposed as the best descriptors of these trends. Average reductions in nvPM mass, number, and sizes of 73%, 54% and 17% respectively, were observed for a near-zero aromatic ATJ fuel compared to a reference Jet A1 fuel, with minimal changes to measured gaseous pollutants. It is noted that without size dependant system loss corrections, nvPM number reductions were overreported (~6% for the ATJ fuel) due to the smaller particle sizes with increasing fuel hydrogen content. It was hypothesised that observed nvPM deviations from the fuel hydrogen content trends were due to fuel physical properties affecting atomisation, however no correlations were found greater than the measurement uncertainty and combustor rig variability.This study provides a unique dataset intended to facilitate combustion model validation, providing full details of combustor geometry, flow conditions and rig conditions, along with the representative combustor exit nvPM and gaseous data.

The mass absorption cross-section (MAC) of combustion-generated soot is used in pollution and emis-sions measurements to quantify the mass concentration of soot and in atmospheric modelling to predict the radiative effects of soot on climate. Previous work has suggested that the MAC of soot particles may change with their size, due to (1) internal scattering among monomers in the soot aggregate, (2) the correlation of soot primary-particle diameter with aggregate size, (3) quantum confinement effects, or (4) a size-dependent degree of soot graphitization. Here, we report a size-dependent MAC for ex-situ soot sampled from two commercially available diffusion-flame soot generators, one aviation turbine engine, and one diesel generator. We also incorporate literature data. We show that the MAC increases with aggregate size until a plateau is reached at single particle masses between 4 and 30 fg (approxi-mately 300-650 nm soot mobility diameter). The smallest particles may have MACs 50%-80% smaller than the largest, depending on the source, while the largest particles have MACs within the range re-ported by previous measurements on polydisperse samples. Moreover, we show that models of hy-potheses (1), (2), and (3) do not describe our measurement results, leaving hypothesis (4) as the only remaining candidate.Crown Copyright (c) 2022 Published by Elsevier Ltd. All rights reserved.

We report here the first implementation of chemically specific imaging in the exhaust plume of a gas turbine typical of those used for propulsion in commercial aircraft. The method used is chemical species tomography (CST) and the target species is CO2, absorbing in the near-infrared at 1999.4 nm. A total of 126 beams propagate transverse to the plume axis, along 7 m paths in a coplanar geometry, to probe a central region of diameter ≈1.5m. The CO2 absorption spectrum is measured using tunable diode laser spectroscopy with wavelength modulation, using the second harmonic to first harmonic (2f/1f) ratio method. The engine is operated over the full range of thrust, while data are recorded in a quasi-simultaneous mode at frame rates of 1.25 and 0.3125 Hz. Various data inversion methodologies are considered and presented for image reconstruction. At all thrust levels a persistent ring structure of high CO2 concentration is observed in the central region of the measurement plane, with a raised region in the middle of the plume assumed to be due to the engine's boat tail. With its potential to target various exhaust species, the CST method outlined here offers a new approach to turbine combustion research, turbine engine development, and aviation fuel research and development.

A new regulatory standard for non-volatile particulate matter (nvPM) mass-based emissions from aircraft engines has been adopted by the International Civil Aviation Organisation. One of the instruments used for the regulatory nvPM mass emissions measurements in aircraft engine certification tests is the Artium Technologies LII 300, which is based on laser-induced incandescence. The LII 300 response has been shown in some cases to vary with the type of black carbon particle measured. Hence it is important to identify a suitable black carbon emission source for instrument calibration. In this study, the relationship between the nvPM emissions produced by different engine sources and the response of the LII 300 instrument utilising the auto-compensating laser-induced incandescence (AC-LII) method was investigated. Six different sources were used, including a turboshaft helicopter engine, a diesel generator, an intermediate pressure test rig of a single-sector combustor, an auxiliary power unit gas turbine engine, a medium-sized diesel engine, and a downsized turbocharged direct-injection gasoline engine. Optimum LII 300 laser fluence levels were determined for each source and operating condition evaluated. It was found that an optimised laser fluence can be valid for real-time measurements from a variety of sources, where the mass concentration was independent of laser fluence levels covering the typical operating ranges for the various sources. However, it is important to perform laser fluence sweeps to determine the optimum fluence range as differences were observed in the laser fluence required between sources and fuels. We discuss the measurement merits, variability, and best practices in the real-time quantification of nvPM mass concentration using the LII 300 instrument and compare that with other diagnostic techniques, namely absorption-based methods such as photoacoustic spectroscopy (using a photoacoustic extinctiometer, PAX, and a micro soot sensor, MSS) and thermal-optical analysis (TOA). Particle size distributions were also measured using a scanning mobility particle sizer (SMPS). Overall, the LII 300 provides robust and consistent results when compared with the other diagnostic techniques across multiple engine sources and fuels. The results from this study will inform the development of updated calibration protocols to ensure repeatable and reproducible measurements of nvPM mass emissions from aircraft engines using the LII 300.