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  • 1. Boman, Christoffer
    et al.
    Pettersson, Esbjorn
    Westerholm, Roger
    Stockholm University, Faculty of Science, Department of Analytical Chemistry.
    Bostrom, Dan
    Nordin, Anders
    Stove Performance and Emission Characteristics in Residential Wood Log and Pellet Combustion, Part 1: Pellet Stoves2011In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 25, p. 307-314Article in journal (Refereed)
    Abstract [en]

    Stove performance, characteristics, and quantities of gaseous and particulate emissions were determined for two different pellet stoves, varying fuel load, pellet diameter, and chimney draft. This approach aimed at covering variations in emissions from stoves in use today. The extensive measurement campaign included CO, NO(x), organic gaseous carbon, volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs), total particulate matter (PM(tot)) as well as particle mass and number concentrations, size distributions, and inorganic composition. At high load, most emissions were similar. For stove B, operating at high residual oxygen and solely with primary air, the emissions of PM,, and particle numbers were higher while the particles were smaller. Lowering the fuel load, the emissions of CO and hydrocarbons increased dramatically for stove A, which operated continuously also at lower fuel loads. On the other hand for stove B, which had intermittent operation at lower fuel loads, the emissions of hydrocarbons increased only slightly lowering the fuel load, while CO emissions increased sharply, due to high emissions at the end of the combustion cycle. Beside methane, dominating VOCs were ethene, acetylene, and benzene and the emissions of VOC varied in the range 1.1-42 mg/MJ(fuel). PAH emissions (2-340 mu g/MJ(fuel)) were generally dominated by phenanthrene, fluoranthene and pyrene. The PM(tot) values (15-45 mg/MJ(fuel)) were in all cases dominated by fine particles with mass median diameters in the range 100-200 nm, peak mobility diameters of 50-85 nm, and number concentrations in the range 4 x 10(13) to 3 x 10(14) particles/MJ(fuel). During high load conditions, the particulate matter was totally dominated by inorganic particles at 15-25 mg/MJ(fuel) consisting of potassium, sodium, sulfur, and chlorine, in the form of K(2)SO(4), K(3)Na(SO(4))(2), and KCl. The study shows that differences in operation and modulation principles for the tested pellet stoves, relevant for appliances in use today, will affect the performance and emissions significantly, although with lower scattering in the present study compared to compiled literature data.

  • 2. Bylund, Jonas
    What's The Problem With Non-conventional Technology?: The Stockholm Local Investment Programme and the Eco-cycling Districts2003In: Time to turn down energy demand / [ed] Sophie Attali, Eliane Métreau, Mélisande Prône, Kenya Tillerson, Stockholm: European Council for an Energy-Efficient Economy - ECEEE , 2003, p. 853-861Chapter in book (Refereed)
    Abstract [en]

    This paper analyses barriers towards implementation of non-conventional energy and resource efficient technology in the context of urban development. It gives tentative conclusions based on an ongoing Ph.D. dissertation project. The case is the measures the city of Stockholm launched with the help of a Swedish Governmental subsidy program – the Local Investment Program (LIP). The LIP runs from 1998 to 2003 and is intended to help municipalities nationwide adapt to the demands of an ecologically sustainable society. Measures that uses new, or in the terminology of this paper, non-conventional technology are explicitly supported in the program. Stockholm was granted 67 million Euro to subsidize different projects, among them the eco-cycling districts of Hammarby Sjöstad, Östberga and Skärholmen. Experiences reported by the municipal LIP co-ordinators nationwide are that only half of all the programs are realized as intended in the applications. As the project is work in progress this paper will try to answer the following questions: Why are some projects successful and others not? Why are sustainability-measures in these projects not carried out completely? Which agents and mediators do help or hinder the subsidies to become a realized and working technology in the city? What is the problem with non-conventional technology really? What parts does politics, policy and administrative practices as well as ‘rational’ economical behaviours play? Some old obstacles, but are new solutions dependent on unorthodox practice or simply more money? Knowledge on these issues is (still) important for subsequent policies and programs on energy and resource efficiency.

  • 3. Krüger, Jonas
    et al.
    Haugen, Nils E. L.
    Mitra, Dhrubaditya
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Løvås, Terese
    The effect of turbulent clustering on particle reactivity2017In: Proceedings of the Combustion Institute, ISSN 1540-7489, E-ISSN 1873-2704, Vol. 36, no 2, p. 2333-2340Article in journal (Refereed)
    Abstract [en]

    The effect of turbulence on the heterogeneous (solid-fluid) reactions of solid particles is studied numerically with Direct Numerical Simulations (DNS). A simplified reaction system is used, where the solid-fluid reaction is represented by a single isothermal reaction step. It is found that, due to the clustering of particles by the isotropic turbulence, the overall reaction rate is entirely controlled by the turbulence for large Damkohler numbers. The particle clustering significantly slows down the reaction rate for increasing Damkohler numbers which reaches an asymptotic limit that can be analytically derived. This implies that the effect of turbulence on heterogeneously reacting particles should be included in models that are used in CFD simulations of e. g. char burnout in combustors or gasifiers. Such a model, based on the chemical and turbulent time scales, is here proposed for the heterogeneous reaction rate in the presence of turbulence.

  • 4.
    Liberman, Michael
    et al.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Wang, Cheng
    Qian, Chengeng
    Liu, JianNan
    Influence of chemical kinetics on spontaneous waves and detonation initiation in highly reactive and low reactive mixtures2019In: Combustion theory and modelling, ISSN 1364-7830, E-ISSN 1741-3559, Vol. 23, no 3, p. 467-495Article in journal (Refereed)
    Abstract [en]

    Understanding the mechanisms of explosions is important for minimising devastating hazards. Due to the complexity of real chemistry, a single-step reaction mechanism is usually used for theoretical and numerical studies. The purpose of this study is to look more deeply into the influence of chemistry on detonation initiated by a spontaneous wave. The results of high-resolution simulations performed for one-step models are compared with simulations for detailed chemical models for highly reactive and low reactive mixtures. The calculated induction times for H-2/air and for CH4/air are validated against experimental measurements for a wide range of temperatures and pressures. It is found that the requirements in terms of temperature and size of the hot spots, which can produce a spontaneous wave capable to initiate detonation, are quantitatively and qualitatively different for one-step models compared to detailed chemical models. The time and locations when the exothermic reaction affects the coupling between the pressure wave and spontaneous wave are considerably different for a one-step and detailed models. The temperature gradients capable to produce detonation and the corresponding size of hot spots are much shallower and, correspondingly, larger than those predicted using one-step models. The impact of the detailed chemical model is particularly pronounced for the methane-air mixture. In this case, not only the hot spot size is much greater than that predicted by a one-step model, but even at the elevated pressure, the initiation of detonation by a temperature gradient is possible only if the temperature outside the gradient is rather high, so that can ignite a thermal explosion. The obtained results suggest that the one-step models do not reproduce correctly the transient and ignition processes, so that interpretation of the simulations performed using a one-step model for understanding mechanisms of flame acceleration, DDT and the origin of explosions must be considered with great caution.

  • 5.
    Mille, Christian
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Corkery, Robert W.
    KTH Royal Inst Technol, Div Phys Chem, Dept Chem, Stockholm.
    A structural and thermal conductivity study of highly porous, hierarchical polyhedral nanofoam shells made by condensing silica in microemulsion films on the surface of emulsified oil drops2013In: Journall of Material Chemistry A, ISSN 2050-7488, Vol. 1, no 5, p. 1849-1859Article in journal (Refereed)
    Abstract [en]

    Light-weight solid foams are utilized in applications such as packaging and insulation mainly due to their intrinsically high porosity, low relative density and associated mechanical and transport properties. Here hollow core spherical shells are prepared with walls made of a polyhedral silica nanofoam with open cells. A microemulsion film at the oil-water interface of oil droplets is used as a soft structural template for the condensation of soluble silica species. The microemulsion sets the length scale of the monodisperse silica nanofoam cells, and the emulsion droplets set the micron-scale dimensions of the polydisperse spherical shells. Porosity is achieved by removing the templates and oils, leaving pure low-density silica. This results in a hierarchically structured, highly porous shell foam material that packs into beds with a measured porosity of approximately 97.3%, well into the range of silica aerogels. Using a combination of electron microscopy, small-angle synchrotron X-ray diffraction and nitrogen physisorption, an accurate structural model for the nanofoam shells is constructed. The material is shown to be comprised of open-cell foams that are structurally analogous to dry polyhedral soap froths having minimal surface partitions, and Plateau boundaries. The primary polyhedral nanofoam cells are 30 nm in diameter connected by 7 nm cylindrical windows. These nanofoams form spherical monolithic shells with volume average mean diameter of 41 microns and shell thickness of 0.7 microns. Simple models for the thermal conductivity of these nanofoam shell materials are constructed that include accounting for the nanoscale effects on gaseous and solid thermal conductivity. These are compared to the measured value of 0.041 W m(-1) K-1. These materials represent new structures in the family of self-assembled, highly porous silica materials and are potentially useful in packaging and insulation and other applications due to their light weight and/or intrinsically low thermal conductivity and associated mechanical and transport properties.

  • 6. Pettersson, Esbjorn
    et al.
    Boman, Christoffer
    Westerholm, Roger
    Stockholm University, Faculty of Science, Department of Analytical Chemistry.
    Bostrom, Dan
    Nordin, Anders
    Stove Performance and Emission Characteristics in Residential Wood Log and Pellet Combustion, Part 2: Wood Stove2011In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 25, p. 315-323Article in journal (Refereed)
    Abstract [en]

    The characteristics and quantities of a large number of gaseous and particulate emission components during combustion in a residential wood log stove with variations in fuel, appliance and operational conditions were determined experimentally. The measurement campaign included CO, NO(x), organic gaseous carbon (OGC), volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs), total particulate matter (PM(tot)) as well as particle mass and number concentrations, size distributions, and inorganic composition. CO varied in the range of 1100 to 7200 mg/MJ(fuel), while OGC varied from 210 to 3300 mg/MJ(fuel). Dominating VOCs were methane, followed by ethene, acetylene, and benzene. Methane varied from 9 to 1600 mg/MJ(fuel). The nonmethane volatile organic compound (NMVOC) emissions were in the range of 20-2300 mg/MJ(fuel). The PAH(tot) emissions varied from 1.3 to 220 mg/MJ(fuel), in most cases dominated by phenantrene, fluoranthene, and pyrene. PM(tot) were in all cases dominated by fine particles and varied in the range 38-350 mg/MJ(fuel). The mass median particle diameters and the peak mobility diameters of the fine particles varied in the range 200-320 and 220-330 nm, respectively, and number concentrations in the range of 1-4 x 10(13) particles/MJ(fuel). Air starved conditions, at high firing intensity, gave the highest emissions, especially for hydrocarbons. This type of condition is seldom considered, though it may occur occasionally. The emissions from Swedish wood stoves, comparing a Swedish field study, are covered fairly well with the applied methodology, but other field studies report considerably higher emissions especially for diluted particle sampling.

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