Research

Please contact Dr Marc Stettler (m.stettler@imperial.ac.uk) if you have any questions.

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  • Journal article
    Popoola OAM, Carruthers D, Lad C, Bright VB, Mead M, Stettler MEJ, Saffell JR, Jons RLet al., 2018,

    Use of networks of low cost air quality sensors to quantify air quality in urban settings

    , Atmospheric Environment, Vol: 194, Pages: 58-70, ISSN: 1352-2310

    Low cost sensors are becoming increasingly available for studying urban air quality. Here we show how such sensors, deployed as a network, provide unprecedented insights into the patterns of pollutant emissions, in this case at London Heathrow Airport (LHR). Measurements from the sensor network were used to unequivocally distinguish airport emissions from long range transport, and then to infer emission indices from the various airport activities. These were used to constrain an air quality model (ADMS-Airport), creating a powerful predictive tool for modelling pollutant concentrations. For nitrogen dioxide (NO2), the results show that the non-airport component is the dominant fraction (∼75%) of annual NO2 around the airport and that despite a predicted increase in airport related NO2 with an additional runway, improvements in road traffic fleet emissions are likely to more than offset this increase. This work focusses on London Heathrow Airport, but the sensor network approach we demonstrate has general applicability for a wide range of environmental monitoring studies and air pollution interventions.
  • Conference paper
    Ainalis D, Achurra-Gonzalez P, Gaudin A, Garcia de la Cruz JM, Angeloudis P, Ochieng WY, Stettler MEJet al., 2018,

    Ultra-Capacitor based kinetic energy recovery system for heavy goods vehicles

    , 15th International Symposium on Heavy Vehicle Transport Technology, Publisher: International Forum for Heavy Vehicle Transport & Technology

    The Climate Change Act 2008 commits the UK to reduce the Greenhouse Gas emissions by 80% by 2050 relative to 1990 levels. While Heavy Goods Vehicles and buses contribute about 4% of the total Greenhouse Gas emissions in the UK, these emissions only decrease by 10% between 1990 and 2015. Urban areas are particularly susceptible to emissions and can have a significant impact upon the health of residents. For Heavy Goods Vehicles, braking losses are one of the most significant losses. A Kinetic Energy Recovery System can help reduce these emissions, and increase fuel efficiency by up to 30 %. This paper describes an InnovateUK funded project aimed at evaluating the technical and economic feasibility of a retrofitted Kinetic Energy Recovery System on Heavy Goods Vehicles through an operational trial, controlled emissions and fuel tests, and numerical modelling. A series of preliminary results using a numerical vehicle model is compared with operational data, along with simulations comparing the fuel efficiency of a Heavy Goods Vehicle with and without the KERS.
  • Journal article
    O'Driscoll R, Stettler MEJ, Molden N, Oxley T, ApSimon HMet al., 2017,

    Real world CO2 and NOx emissions from 149 Euro 5 and 6 diesel, gasoline and hybrid passenger cars

    , Science of the Total Environment, Vol: 621, Pages: 282-290, ISSN: 0048-9697

    In this study CO2 and NOx emissions from 149 Euro 5 and 6 diesel, gasoline and hybrid passenger cars were compared using a Portable Emissions Measurement System (PEMS). The models sampled accounted for 56% of all passenger cars sold in Europe in 2016. We found gasoline vehicles had CO2 emissions 13-66% higher than diesel. During urban driving, the average CO2 emission factor was 210.5 (sd. 47) gkm-1 for gasoline and 170.2 (sd. 34) gkm-1 for diesel. Half the gasoline vehicles tested were Gasoline Direct Injection (GDI). Euro 6 GDI engines <1.4ℓ delivered ~17% CO2 reduction compared to Port Fuel Injection (PFI). Gasoline vehicles delivered an 86-96% reduction in NOx emissions compared to diesel cars. The average urban NOx emission from Euro 6 diesel vehicles 0.44 (sd. 0.44) gkm-1 was 11 times higher than for gasoline 0.04 (sd. 0.04) gkm-1. We also analysed two gasoline-electric hybrids which out-performed both gasoline and diesel for NOx and CO2. We conclude action is required to mitigate the public health risk created by excessive NOx emissions from modern diesel vehicles. Replacing diesel with gasoline would incur a substantial CO2 penalty, however greater uptake of hybrid vehicles would likely reduce both CO2 and NOx emissions. Discrimination of vehicles on the basis of Euro standard is arbitrary and incentives should promote vehicles with the lowest real-world emissions of both NOx and CO2.
  • Journal article
    Koudis GS, Hu SJ, North RJ, Majumdar A, Stettler MEJet al., 2017,

    The impact of aircraft takeoff thrust setting on NO<inf>X</inf> emissions

    , Journal of Air Transport Management, Vol: 65, Pages: 191-197, ISSN: 0969-6997

    Reduced thrust takeoff has the potential to reduce aircraft-related NO X emissions at airports, however this remains to be investigated using flight data. This paper analyses the effect of takeoff roll thrust setting variability on the magnitude and spatial distribution of NO X emissions using high-resolution data records for 497 Airbus A319 activities at London Heathrow. Thrust setting varies between 67 and 97% of maximum, and aircraft operating in the bottom 10th percentile emit on average 514 g less NO X per takeoff roll (32% reduction) than the top 10th percentile, however this is dependent on takeoff roll duration. Spatial analysis suggests that peak NO X emissions, corresponding to the start of the takeoff roll, can be reduced by up to 25% by adopting reduced thrust takeoff activities. Furthermore, the length of the emission source also decreases. Consequently, the use of reduced thrust takeoff may enable improved local air quality at airports.
  • Journal article
    Koudis GS, Hu J, Majumdar A, Jones R, Stettler MEJet al., 2017,

    Airport emissions reductions from reduced thrust takeoff operations

    , Transportation Research Part D: Transport and Environment, Vol: 52, Pages: 15-28, ISSN: 1361-9209

    Given forecast aviation growth, many airports are predicted to reach capacity and require expansion. However, pressure to meet air quality regulations emphasises the importance of efficient ground-level aircraft activities to facilitate growth. Operational strategies such as reducing engine thrust setting at takeoff can reduce fuel consumption and pollutant emissions; however, quantification of the benefits and consistency of its use have been limited by data restrictions. Using 3,336 high-resolution flight data records, this paper analyses the impact of reduced thrust takeoff at London Heathrow. Results indicate that using reduced thrust takeoff reduces fuel consumption, nitrogen oxides (NOX) and black carbon (BC) emissions by 1.0-23.2%, 10.7-47.7%, and 49.0-71.7% respectively, depending on aircraft-engine combinations relative to 100% thrust takeoff. Variability in thrust settings for the same aircraft-engine combination and dependence on takeoff weight (TOW) is quantified. Consequently, aircraft-engine specific optimum takeoff thrust settings that minimise fuel consumption and pollutant emissions for different aircraft TOWs are presented. Further reductions of 1.9%, 5.8% and 6.5% for fuel consumption, NOX and BC emissions could be achieved, equating to reductions of approximately 0.4%, 3.5% and 3.3% in total ground level fuel consumption, NOX and BC emissions. These results quantify the contribution that reduced thrust operations offer towards achieving industry environmental targets and air quality compliance, and imply that the current implementation of reduced thrust takeoff at Heathrow is near optimal, considering operational and safety constraints.
  • Journal article
    Olfert JS, Dickau M, Momenimovahed A, Saffaripour M, Thompson K, Smallwood G, Stettler MEJ, Boies AM, Sevcenco Y, Crayford A, Johnson Met al., 2017,

    Effective density and volatility of particles sampled from a helicopter gas turbine engine

    , Aerosol Science and Technology, Vol: 51, Pages: 704-714, ISSN: 0278-6826

    The effective density and size-resolved volatility of particles emitted from a Rolls-Royce Gnome helicopter turboshaft engine are measured at two engine speed settings (13,000 and 22,000 RPM). The effective density of denuded and undenuded particles were measured. The denuded effective densities are similar to the effective densities of particles from a gas turbine with a double annular combustor as well as a wide variety of internal combustion engines. The denuded effective density measurements were also used to estimate the size and number of primary particles in the soot aggregates. The primary particle size estimates show that the primary particle size was smaller at lower engine speed (in agreement with transmission electron microscopy analysis). As a demonstration, the size-resolved volatility of particles emitted from the engine are measured with a system consisting of a differential mobility analyzer, centrifugal particle mass analyzer, condensation particle counter, and catalytic stripper. This system determines the number distributions of particles that contain or do not contain non-volatile material, and the mass distributions of non-volatile material, volatile material condensed onto the surface of non-volatile particles, and volatile material forming independent particles (e.g. nucleated volatile material). It was found that the particulate at 13,000 RPM contained a measurable fraction of purely volatile material with diameters below ∼25 nm and had a higher mass fraction of volatile material condensed on the surface of the soot (6–12%) compared to the 22,000 RPM condition (1–5%). This study demonstrates the potential to quantify the distribution of volatile particulate matter and gives additional information to characterize sampling effects with regulatory measurement procedures.
  • Journal article
    Bishop JDK, Stettler MEJ, Molden N, Boies AMet al., 2016,

    Engine maps of fuel use and emissions from transient driving cycles

    , Applied Energy, Vol: 183, Pages: 202-217, ISSN: 0306-2619

    Air pollution problems persist in many cities throughout the world, despite drastic reductions in regulated emissions of criteria pollutants from vehicles when tested on standardised driving cycles. New vehicle emissions regulations in the European Union and United States require the use of OBD and portable emissions measurement systems (PEMS) to confirm vehicles meet specified limits during on-road operation. The resultant in-use testing will yield a large amount of OBD and PEMS data across a range of vehicles. If used properly, the availability of OBD and PEMS data could enable greater insight into the nature of real-world emissions and allow detailed modelling of vehicle energy use and emissions. This paper presents a methodology to use this data to create engine maps of fuel use and emissions of nitrous oxides (NOx), carbon dioxide (CO2) and carbon monoxide (CO). Effective gear ratios, gearbox shift envelopes, candidate engine maps and a set of vehicle configurations are simulated over driving cycles using the ADVISOR powertrain simulation tool. This method is demonstrated on three vehicles – one truck and two passenger cars – tested on a vehicle dynamometer and one driven with a PEMS. The optimum vehicle configuration and associated maps were able to reproduce the shape and magnitude of observed fuel use and emissions on a per second basis. In general, total simulated fuel use and emissions were within 5% of observed values across the three test cases. The fitness of this method for other purposes was demonstrated by creating cold start maps and isolating the performance of tailpipe emissions reduction technologies. The potential of this work extends beyond the creation of vehicle engine maps to allow investigations into: emissions hot spots; real-world emissions factors; and accurate air quality modelling using simulated per second emissions from vehicles operating in over any driving cycle.
  • Journal article
    Worth DJ, Stettler MEJ, Dickinson P, Hegarty K, Boies AMet al., 2016,

    Characterization and evaluation of methane oxidation catalysts for dual-fuel diesel and natural gas engines

    , Emission Control Science and Technology, Vol: 2, Pages: 204-214, ISSN: 2199-3629

    The UK has incentivized the use of natural gas in heavy goods vehicles (HGVs) by converting to dual-fuel (DF) diesel-natural gas systems to reduce noxious and greenhouse gas emissions. Laboratory and on-road measurements of DF vehicles have demonstrated a decrease in CO2 emissions relative to diesel, but there is an increase in greenhouse gas (CO2e) emissions because of unburned methane. Decreasing tailpipe emissions of methane via after-treatment devices in lean-burn compression ignition engines is a challenge because of low exhaust temperatures (∼400 °C) and the presence of water vapor. In this study, six commercially available methane oxidation catalysts (MOCs) were tested for their application in DF HGV vehicles. Each MOC was characterized in terms of the catalyst platinum group metal (PGM) loading (both Pd and Pt), particle size, catalytic surface area, and Pd:Pt ratio. In addition, the washcoat surface area, pore volume, and pore size were evaluated. The MOC conversion efficiency was evaluated in controlled methane-oxidation experiments with varying temperatures, flow rates, and gas compositions. Characteristic-conversion efficiency correlations demonstrate that the influential MOC characteristics were PGM loading (both Pd and Pt), Pd:Pt ratio, washcoat surface area, and washcoat pore volume. With 90 % methane oxidation at less than 400 °C in DF HGV exhaust conditions, sample 1 had the highest conversion efficiency because of a high PGM loading (330 g/ft3, 12,000 g/m3), a 5.9 Pd:Pt ratio, a high alumina washcoat surface area of 20 m2/cm3, and 74-mm3/cm3 pore volume. Additional studies showed increased MOC conversion efficiency with decreasing gas hourly space velocities (GHSVs) and increasing methane concentrations.
  • Journal article
    O'Driscoll R, ApSimon HM, Oxley T, Molden N, Stettler MEJ, Thiyagarajah Aet al., 2016,

    A Portable Emissions Measurement System (PEMS) study of NO<inf>x</inf> and primary NO<inf>2</inf> emissions from Euro 6 diesel passenger cars and comparison with COPERT emission factors

    , Atmospheric Environment, Vol: 145, Pages: 81-91, ISSN: 1352-2310

    Real world emissions of oxides of nitrogen (NOx) often greatly exceed those achieved in the laboratory based type approval process. In this paper the real world emissions from a substantial sample of the latest Euro 6 diesel passenger cars are presented with a focus on NOx and primary NO2. Portable Emissions Measurement System (PEMS) data is analysed from 39 Euro 6 diesel passenger cars over a test route comprised of urban and motorway sections. The sample includes vehicles installed with exhaust gas recirculation (EGR), lean NOx traps (LNT), or selective catalytic reduction (SCR). The results show wide variability in NOx emissions from 1 to 22 times the type approval limit. The average NOx emission, 0.36 (sd. 0.36) g km−1, is 4.5 times the Euro 6 limit. The average fraction primary NO2 (fNO2) is 44 (sd. 20) %. Higher emissions during the urban section of the route are attributed to an increased number of acceleration events. Comparisons between PEMS measurements and COPERT speed dependent emissions factors show PEMS measurements to be on average 1.6 times higher than COPERT estimates for NOx and 2.5 times for NO2. However, by removing the 5 most polluting vehicles average emissions were reduced considerably.
  • Journal article
    Dickau M, Olfert J, Stettler MEJ, Boies A, Momenimovahed A, Thomson K, Smallwood G, Johnson Met al., 2016,

    Methodology for quantifying the volatile mixing state of an aerosol

    , Aerosol Science and Technology, Vol: 50, Pages: 759-772, ISSN: 0278-6826

    Mixing state refers to the relative proportions of chemical species in an aerosol, and the way these species are combined; either as a population where each particle consists of a single species (‘externally mixed’) or where all particles individually consist of two or more species (‘internally mixed’) or the case where some particles are pure and some particles consist of multiple species. The mixing state affects optical and hygroscopic properties, and quantifying it is therefore important for studying an aerosol's climate impact. In this article, we describe a method to quantify the volatile mixing state of an aerosol using a differential mobility analyzer, centrifugal particle mass analyzer, catalytic denuder, and condensation particle counter by measuring the mass distributions of the volatile and non-volatile components of an aerosol and determining how the material is mixed within and between particles as a function of mobility diameter. The method is demonstrated using two aerosol samples from a miniCAST soot generator, one with a high elemental carbon (EC) content, and one with a high organic carbon (OC) content. The measurements are presented in terms of the mass distribution of the volatile and non-volatile material, as well as measures of diversity and mixing state parameter. It was found that the high-EC soot nearly consisted of only pure particles where 86% of the total mass was non-volatile. The high-OC soot consisted of either pure volatile particles or particles that contained a mixture of volatile and non-volatile material where 8% of the total mass was pure volatile particles and 70% was non-volatile material (with the remaining 22% being volatile material condensed on non-volatile particles). © 2016 American Association for Aerosol Research
  • Journal article
    Stettler MEJ, Midgley WJB, Swanson JJ, Cebon D, Boies AMet al., 2016,

    Greenhouse gas and noxious emissions from dual fuel diesel and natural gas heavy goods vehicles

    , Environmental Science and Technology (Washington), Vol: 50, Pages: 2018-2026, ISSN: 0013-936X

    Dual fuel diesel and natural gas heavy goods vehicles (HGVs) operate on a combination of the two fuels simultaneously. By substituting diesel for natural gas, vehicle operators can benefit from reduced fuel costs and as natural gas has a lower CO2 intensity compared to diesel, dual fuel HGVs have the potential to reduce greenhouse gas (GHG) emissions from the freight sector. In this study, energy consumption, greenhouse gas and noxious emissions for five after-market dual fuel configurations of two vehicle platforms are compared relative to their diesel-only baseline values over transient and steady state testing. Over a transient cycle, CO2 emissions are reduced by up to 9%; however, methane (CH4) emissions due to incomplete combustion lead to CO2e emissions that are 50–127% higher than the equivalent diesel vehicle. Oxidation catalysts evaluated on the vehicles at steady state reduced CH4 emissions by at most 15% at exhaust gas temperatures representative of transient conditions. This study highlights that control of CH4 emissions and improved control of in-cylinder CH4 combustion are required to reduce total GHG emissions of dual fuel HGVs relative to diesel vehicles.
  • Journal article
    Boies AM, Stettler MEJ, Swanson JJ, Johnson TJ, Olfert JS, Johnson M, Eggersdorfer ML, Rindlisbacher T, Wang J, Thomson K, Smallwood G, Sevcenco Y, Walters D, Williams PI, Corbin J, Mensah AA, Symonds J, Dastanpour R, Rogak SNet al., 2015,

    Particle Emission Characteristics of a Gas Turbine with a Double Annular Combustor

    , AEROSOL SCIENCE AND TECHNOLOGY, Vol: 49, Pages: 842-855, ISSN: 0278-6826
  • Journal article
    Omu A, Rysanek A, Stettler M, Choudhary Ret al., 2015,

    Economic, Climate Change, and Air Quality Analysis of Distributed Energy Resource Systems

    , INTERNATIONAL CONFERENCE ON COMPUTATIONAL SCIENCE, ICCS 2015 COMPUTATIONAL SCIENCE AT THE GATES OF NATURE, Vol: 51, Pages: 2147-2156, ISSN: 1877-0509
  • Journal article
    Simone NW, Stettler MEJ, Barrett SRH, 2013,

    Rapid estimation of global civil aviation emissions with uncertainty quantification

    , TRANSPORTATION RESEARCH PART D-TRANSPORT AND ENVIRONMENT, Vol: 25, Pages: 33-41, ISSN: 1361-9209
  • Journal article
    Stettler MEJ, Swanson JJ, Barrett SRH, Boies AMet al., 2013,

    Updated Correlation Between Aircraft Smoke Number and Black Carbon Concentration

    , AEROSOL SCIENCE AND TECHNOLOGY, Vol: 47, Pages: 1205-1214, ISSN: 0278-6826
  • Journal article
    Stettler MEJ, Boies AM, Petzold A, Barrett SRHet al., 2013,

    Global Civil Aviation Black Carbon Emissions

    , ENVIRONMENTAL SCIENCE & TECHNOLOGY, Vol: 47, Pages: 10397-10404, ISSN: 0013-936X
  • Journal article
    Yim SHL, Stettler MEJ, Barrett SRH, 2013,

    Air quality and public health impacts of UK airports. Part II: Impacts and policy assessment

    , ATMOSPHERIC ENVIRONMENT, Vol: 67, Pages: 184-192, ISSN: 1352-2310
  • Journal article
    Stettler MEJ, Eastham S, Barrett SRH, 2011,

    Air quality and public health impacts of UK airports. Part I: Emissions

    , ATMOSPHERIC ENVIRONMENT, Vol: 45, Pages: 5415-5424, ISSN: 1352-2310

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