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  • 1.
    Andrae, Johan
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Björnbom, Pehr
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Wall Effects of Laminar Hydrogen Flames over Platinum and Inert Surfaces2000In: AIChE Journal, ISSN 0001-1541, E-ISSN 1547-5905, Vol. 46, no 7, p. 1454-1460Article in journal (Refereed)
    Abstract [en]

    Different aspects of wall effects in the combustion of lean, laminar and stationary hydrogen flames in an axisymmetric boundary-layer flow were studied using numerical simulations with the program CRESLAF. The importance of the chemical wall effects compared to thermal wall effects caused by heat transfer to a cold wall was investigated in the reaction zone by using different combustion systems at atmospheric pressure. Surface mechanisms include a catalytic surface, an inert surface that promotes radical recombinations, and a completely inert wall used as reference was the simplest possible boundary condition. The analysis of the results show that for the richer combustion case ( = 0.5) the surface chemistry gives significant wall effects, while the thermal and velocity boundary layer gives rather small effects. But for the leaner combustion case ( = 0.1) the thermal and velocity boundary layer gives more significant wall effects, while surface chemistry gives less significant wall effects compared to the other case. As expected, the overall wall effects were more pronounced for the leaner combustion case.

  • 2.
    Andrae, Johan
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Björnbom, Pehr
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Edsberg, Lennart
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Numerical studies of wall effects with laminar methane flames2002In: Combustion and Flame, ISSN 0010-2180, E-ISSN 1556-2921, Vol. 128, no 1-2, p. 165-180Article in journal (Refereed)
    Abstract [en]

    Wall effects in the combustion of lean methane mixtures have been studied numerically using the CHEMKIN software. To gain a deeper understanding of the flame-wall interaction in lean burn combustion, and in particular the kinetic and thermal effects, we have simulated lean and steady methane/air flames in a boundary layer flow. The gas-phase chemistry is modeled with the GRI mechanism version 1.2. Boundary conditions include an inert wall, a recombination wall and catalytic combustion of methane. Different pressures, wall temperatures and fuel-air ratios are used to address questions such as which part of the wall effects is most important at a given set of conditions. As the results are analyzed it can be seen that the thermal wall effects are more significant at the lower wall temperature (600 K) and the wall can essentially be modeled as chemical inert for the lean mixtures used. At the higher wall temperature (1,200 K), the chemical wall effects become more significant and at the higher pressure (10 atm) the catalytic surface retards homogeneous combustion of methane more than the recombination wall because of product inhibition. This may explain the increased emissions of unburned fuel observed in engine studies, when using catalytic coatings on the cylinder walls. The overall wall effects were more pronounced for the leaner combustion case (phi = 0.2). When the position of the reaction zone obtained from the boundary layer calculations is compared with the results from a one-dimensional premixed flame model, there is a small but significant difference except at the richer combustion case (phi = 0.4) at atmospheric pressure, where the boundary layer model may not predict the flame position for the given initial conditions.

  • 3.
    Andrae, Johan
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Björnbom, Pehr
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Edsberg, Lennart
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Eriksson, L-E
    Volvo Aero Corporation.
    A Numerical Study of Sidewall Quenching with Propane/Air Flames2002In: Proceedings of the Combustion Institute, ISSN 0082-0784, E-ISSN 1878-027X, Vol. 29, p. 789-795Article in journal (Refereed)
    Abstract [en]

    The head-on (i.e., stagnation) configuration has generally been used to numerically and experimentally characterize the flame-wall interaction with complex chemistry and multicomponent transport. Other studies have treated the transient case of a flame propagating toward a wall, and combustion in a boundary layer has also been dealt with. In this paper, a two-dimensional stationary model has been used to study the sidewall quenching,of laminar propane/air flames in a boundary-layer flow. This geometry may be described as a flame parallel to the wall that is swept away with a laminar boundary-layer flow while propagating toward and interacting with the wall. The main purpose has been to examine the extent to which the flame can propagate toward the cooled wall for lean flames compared to stoichiometric flames. A detailed kinetic model is used to examine the oxidation of both the fuel and the intermediate hydrocarbons (IHCs). For stoichiometric and near stoichiometric mixtures, the thermal coupling between the flame and the wall is small but significant. However, for very lean flames, the thermal coupling between the flame and the wall is found to be very significant. The intermediate hydrocarbons are the dominant emissions for stoichiometric and near-stoichiometric flames in contrast to the leaner flames in which the fuel becomes more significant. This implies that the IHCs are very important for the overall hydrocarbon emissions from flame quenching; as a result detailed kinetics of complex fuels should be used when determining the unburned hydrocarbon emissions.

  • 4.
    Andrae, Johan
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Björnbom, Pehr
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Edsberg, Lennart
    Eriksson, L-E
    Kinetic and Transport Effects of Pressurized Methane Flames in a Boundary Layer2003In: Combustion and Flame, ISSN 0010-2180, E-ISSN 1556-2921, Vol. 133, no 4, p. 503-506Article in journal (Refereed)
    Abstract [en]

    We have recently modeled combustion of lean methane-air [1] mixtures in a boundary layer flow using the program CRESLAF [2, 3 and 4]. A uniform fuel-air mixture above the auto-ignition temperature was introduced at the inlet edge of the wall, which gave an arrested flame zone, propagating in the upstream direction with a local flame speed that is equal and opposite to the local flow velocity. We compared the interaction of this flame with three model wall materials representing three idealized cases from a chemical point of view, a completely inert wall, a radical recombining wall, and a wall supporting catalytic combustion.

    Here we report on an analogous study of a flame geometry that may be considered a combination of a one-dimensional flame propagating towards a wall and the combustion of a uniform fuel-air mixture in a boundary layer flow. In contrast to our previous work [1] where we had a uniform inlet flow composition consisting of unburnt gas, here there is only unburnt gas close to the walls while there is burnt gas in the center of the channel. The present study concerns lean pressurized methane flames propagating toward hot isothermal walls where chemistry on the wall is considered important.

    The main purpose is to compare the results with those obtained in Ref. [1], which enables us, for the same flow field (boundary layer flow), to compare the effect of flame geometry on the wall effects. We have found and have been able to explain theoretically that such subtle changes of the flame geometry, which would be rather difficult to study experimentally, may have surprisingly significant effects on the combustion process.

  • 5.
    Andrae, Johan
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Björnbom, Pehr
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Glarborg, P
    A Design Concept to Reduce Fuel NOx in Catalytic Combustion of Gasified Biomass2003In: AIChE Journal, ISSN 0001-1541, E-ISSN 1547-5905, Vol. 49, no 8, p. 2149-2157Article in journal (Refereed)
    Abstract [en]

    A reactor concept was studied to reduce the fuel NOx at conditions relevant to catalytic combustion of gasified biomass containing ammonia. A hybrid reactor is modeled with passive and active channels, where only part of the fuel is combusted catalytically in the active channels. The completion of the reactions is carried out in the subsequent homogeneous zone. The air-fuel ratio is found to be the most important parameter for the NOx emission level. When the primary zone is operated fuel-lean, no favorable conditions are established for selective noncatalytic reduction reactions in the homogeneous zone, and the fuel nitrogen is largely oxidized to NO. However, if the air supply to the monolith is staged rich-lean, a 95% reduction in NO is possible. The NO reduction is facilitated by the remaining fuel components, CO and H-2.

  • 6.
    Andrae, Johan C. G.
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Johansson, A.
    Björnbom, Pehr
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Rosen, A.
    OH desorption energies for a palladium catalyst characterised by kinetic modelling and laser-induced fluorescence2004In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 563, no 03-jan, p. 145-158Article in journal (Refereed)
    Abstract [en]

    A kinetic model for the H-2/O-2 reaction on a polycrystalline palladium catalyst has been constructed using CHEMKIN in order to understand the coverage-dependent OH desorption energy. Each adsorbed oxygen atom was modelled to cover four I'd surface sites. The yield of OH and the water production were measured with laser-induced fluorescence (LIF) and microcalorimetry respectively as a function of the relative hydrogen concentration, alpha(H2). The temperature of the catalyst was 1300 K, the total pressure was 13 Pa and the flow was set to 100 SCCM. In fitting the model to the experimental data, the OH desorption energy E-OH(d) was found to have a first-order coverage dependence according to: E-OH(d)(theta) = E-OH(d)(0) - Btheta, where B is a constant set to 92 kJ/mol. The desorption energy at zero coverage E-OH(d)(0) was determined to be 226 kJ/mol. The model could also qualitatively and quantitatively reproduce the apparent desorption energy as a function of alpha(H2); therefore it is believed that the coverage could be predicted by the model. The values for E-OH(d)(theta) were calculated as a function of alpha(H2). From the results of a sensitivity analysis and rate of production calculations' there are strong reasons to believe that the main water-forming reaction on Pd at 1300 K is the hydrogen addition reaction, H + OH reversible arrow H2O. Enthalpy diagrams for the water-forming reactions are also presented.

  • 7.
    Andrae, Johan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Reaction Engineering.
    Johansson, David
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Reaction Engineering.
    Björnbom, Pehr
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Reaction Engineering.
    Risberg, Per
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Kalghatgi, Gautam
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Cooxidation in the auto-ignition of primary reference fuels and n-heptane/toluene blends2005In: Combustion and Flame, ISSN 0010-2180, E-ISSN 1556-2921, Vol. 140, no 4, p. 267-286Article in journal (Refereed)
    Abstract [en]

    Auto-ignition of fuel mixtures was investigated both theoretically and experimentally to gain further understanding of the fuel chemistry. A homogeneous charge compression ignition (HCCI) engine was run under different operating conditions with fuels of different RON and MON and different chemistries. Fuels considered were primary reference fuels and toluene/n-heptane blends. The experiments were modeled with a single-zone adiabatic model together with detailed chemical kinetic models. In the model validation, co-oxidation reactions between the individual fuel components were found to be important in order to predict HCCI experiments, shock-tube ignition delay time data, and ignition delay times in rapid compression machines. The kinetic models with added co-oxidation reactions further predicted that an n-heptane/toluene fuel with the same RON as the corresponding primary reference fuel had higher resistance to auto-ignition in HCCI combustion for lower intake temperatures and higher intake pressures. However, for higher intake temperatures and lower intake pressures the n-heptane/toluene fuel and the PRF fuel had similar combustion phasing.

  • 8.
    Björnbom, Pehr
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Charge/discharge of an electrochemical supercapacitor electrode pore; non-uniqueness of mathematical models2007In: Electrochemistry communications, ISSN 1388-2481, E-ISSN 1873-1902, Vol. 9, no 2, p. 211-215Article in journal (Refereed)
    Abstract [en]

    A thermodynamic analysis has been done to enhance understanding of the relation between various mathematical models for electrochemical supercapacitor pores. For the same capacitive charge/discharge experiment a variety of one-dimensional mathematical model equations concerning the transport of ions and double layer charge/discharge along the pore are shown to be indistinguishable. Some of those indistinguishable equations could be interpreted as derived from diffusional mechanisms while others appear as derived from migrational mechanisms. Ohmic resistivities and diffusivities obtained in such case are not contradicting results but characterize identical physical processes. The results are valid as long as the assumptions of irreversible thermodynamics of local equilibrium along the pore and of linearization of the flux equations hold.

  • 9.
    Björnbom, Pehr
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Temperature lapse rates at restricted thermodynamic equilibrium in the Earth system2015In: Dynamics of atmospheres and oceans (Print), ISSN 0377-0265, E-ISSN 1872-6879, Vol. 69, p. 26-36Article in journal (Refereed)
    Abstract [en]

    Equilibrium temperature profiles obtained by maximizing the entropy of a column of fluid with a given height and-volume under the influence of gravity are discussed by using numerical experiments. Calculations are made both for the case of an ideal gas and for a liquid with constant isobaric heat capacity, constant compressibility and constant thermal expansion coefficient representing idealized conditions corresponding to atmosphere and ocean. Calculations confirm the classical equilibrium condition by Gibbs that an isothermal temperature profile gives a maximum in entropy constrained by a constant mass and a constant sum of internal and potential energy. However, it was also found that an isentropic profile gives a maximum in entropy constrained by a constant mass and a constant internal energy of the fluid column. On the basis of this result a hypothesis is suggested that the adiabatic lapse rate represents a restricted or transitory and metastable equilibrium state, which has a maximum in entropy with lower value than the maximum in the state with an isothermal lapse rate. This transitory equilibrium state is maintained by passive forces, preventing or slowing down the transition of the system to the final or ultimate equilibrium state.

  • 10.
    Björnbom, Pehr
    KTH.
    Temperature lapse rates at restricted thermodynamic equilibrium. Part II: Saturated air and further discussions2016In: Dynamics of atmospheres and oceans (Print), ISSN 0377-0265, E-ISSN 1872-6879, Vol. 73, p. 76-86Article in journal (Refereed)
    Abstract [en]

    In the first part of this work equilibrium temperature profiles in fluid columns with ideal gas or ideal liquid were obtained by numerically minimizing the column energy at constant entropy, equivalent to maximizing column entropy at constant energy. A minimum in internal plus potential energy for an isothermal temperature profile was obtained in line with Gibbs' classical equilibrium criterion. However, a minimum in internal energy alone for adiabatic temperature profiles was also obtained. This led to a hypothesis that the adiabatic lapse rate corresponds to a restricted equilibrium state, a type of state in fact discussed already by Gibbs. In this paper similar numerical results for a fluid column with saturated air suggest that also the saturated adiabatic lapse rate corresponds to a restricted equilibrium state. The proposed hypothesis is further discussed and amended based on the previous and the present numerical results and a theoretical analysis based on Gibbs' equilibrium theory.

  • 11.
    BURSELL, Martin
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    BJÖRNBOM, Pehr
    KTH, Superseded Departments, Chemical Engineering and Technology.
    A METHOD FOR STUDYING MICROELECTRODES BY MEANS OF MICROMANIPULATORS AS APPLIED TO CARBON AGGLOMERATES FROM OXYGEN REDUCTION ELECTRODE CATALYST1990In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 137, no 1, p. 363-365Article in journal (Refereed)
  • 12.
    Bursell, Martin
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Björnbom, Pehr
    KTH, Superseded Departments, Chemical Engineering and Technology.
    electrochemical investigation of microagglomerates from fc-cathodes1990In: 1990 Fuel cell seminar, 1990, p. 419-421Conference paper (Refereed)
  • 13.
    Fillman, Benny
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Björnbom, Pehr
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Sylwan, Christopher
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Sparr, Mari
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Lindbergh, Göran
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Influence of process parameters on the system efficiency of anatural gas or a gasified biomass fueled MCFC systemManuscript (preprint) (Other academic)
  • 14.
    Johansson, David
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Andrae, Johan
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Björnbom, Pehr
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Coupling of CHEMKIN and MATLAB for HCCI combustion application2004In: International Symposium on Combustion, Abstracts of Works-in-Progress Posters, 2004Conference paper (Refereed)
    Abstract [en]

    In Homogeneous Charge Compression Ignition (HCCI) engine applications a mixture of fuel and oxidizer is compressed in an engine cylinder until self-ignition occurs. Since no flame propagation or fuel-rich regions exists no soot will form and in-cylinder temperatures will be rather low leading to very low NOx emissions. Another benefit is a high, diesel like, efficiency. The problems will HCCI combustion are mainly high hydrocarbon and CO emissions, high peak pressures, control difficulties, etc. A possible way to utilize the benefits is to use a dual mode engine that works in HCCI mode at low and medium loads and in diesel mode at high loads. A way to link CHEMKIN III to the MATLAB environment is presented. The coupling between the programs gives MATLAB access to rate of production, enthalpy and specific heat producing subroutines from the CHEMKIN III package. All modeling is done in MATLAB after the link has been established. The coupling is then used to make a HCCI engine model, consisting of three zones, each of uniform temperatures and composition, of each zone, and the inputs are temperatures of the different zones, pressure and composition of the initial fuel/ox load and engine data. Analysis of a mixture of 84% iso-octane and 16% and n-heptane/air HCCI combustion was presented and compared to experimental results. This is an abstract of a paper presented at the 30th International Symposium on Combustion (Chicago, IL 7/25-30/2004).

  • 15.
    Kiros, Yohannes
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Quatrano, Tamara
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Björnbom, Pehr
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Determination of the thicknesses of the active layer and cathode limiting currents in AFC2004In: Electrochemistry communications, ISSN 1388-2481, E-ISSN 1873-1902, Vol. 6, no 6, p. 526-530Article in journal (Refereed)
    Abstract [en]

    A series of double-layered gas diffusion electrodes with two different electrocatalysts, i.e., Ag and pyrolyzed macrocycle mixture (PMM) were prepared in order to find out the maximum limiting current densities (i(L)) by varying the oxygen partial pressures in 6 M KOH and at 65 degreesC. As optimization of the active (catalyst) layer is important for better utilization of the catalytic reactions for oxygen reduction and thereby attainment of high current density, electrochemical measurements in half-cells were carried out to substantiate the current-thickness relationships. The thicknesses for both the active layers and diffusion layers were determined by using SEM. i(L) for an oxygen concentration simulating that of air was found to be 2.2 A cm(-2) for the PMM with 0.51 mm and 1.6 A cm-2 for the Ag-based catalyst with 0.56 mm thicknesses of the active layer. An overlay of a mathematical model, describing the parameters for determination of i(L), has also been inserted alongside the experimental values.

  • 16.
    Kivisaari, Timo
    et al.
    KTH, Superseded Departments, Chemistry.
    Björnbom, Pehr
    KTH, Superseded Departments, Chemistry.
    Sylwan, Christopher
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Jacquinot, B.
    Jansen, D.
    de Groot, A.
    The feasibility of a coal gasifier combined with a high-temperature fuel cell2004In: Chemical Engineering Journal, ISSN 1385-8947, E-ISSN 1873-3212, Vol. 100, no 03-jan, p. 167-180Article in journal (Refereed)
    Abstract [en]

    The purpose of the study presented in this paper was to find out the feasibility of integrating a 50MW fuel cell system, fed by gas from a coal gasifier. with an existing network for distribution of heat and power. The work presented is the results of the technical evaluation of a 50MW coal fired high-temperature fuel cell power plant. The overall system can be divided into four subsystems including: coal gasification, gas cleaning, power generation and heat recovery. The final system, a entrained flow gasifier combined with standard low-temperature gas cleanup and SOFC, resulted in an overall electrical efficiency of about 47%, and an overall efficiency close to 85%.

  • 17. Lehtinen, T
    et al.
    Sundholm, G
    Holmberg, S
    Sundholm, F
    Björnbom, Pehr
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Bursell, Martin
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Electrochemical characterization of PVDF-based proton conducting membranes for fuel cells1998In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 43, p. 1881-1890Article in journal (Refereed)
    Abstract [en]

    The electrochemical characterization of proton-conducting membranes prepared by irradiation-induced grafting and subsequent sulfonation of PVDF films has been performed. In particular, measurements of the ionic conductivity, oxygen solubility and diffusion in the membranes are presented, as well as kinetic data for the oxygen reduction reaction in a membrane-platinum system and a simulation of the performance of these PVDF-g-PSSA membranes in a solid polymer electrolyte fuel cell using a microcathode technique. At sufficient degrees of grafting (>40%) the conductivity reaches 0.1 Scm−1, well above that of Nafion 117 (DuPont). The PVDF-g-PSSA membranes show lower solubilities and higher diffusion coefficients of oxygen and a higher water uptake than Nafion 117. The microcathode measurements indicate that those PVDF-g-PSSA membranes which have a conductivity higher than that of Nafion 117 may also give improved performance in fuel cell conditions provided that they have the necessary mechanical and chemical stability.

  • 18.
    Malmberg, Helena
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Lundblad, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Björnbom, Pehr
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Modeling an alkaline supercapacitor electrode from activated carbon particlesManuscript (Other academic)
  • 19.
    Malmberg, Helena
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Reaction Engineering.
    Ruiz, Vanesa
    Instituto Nacional del Carbón (CSIC), Oviedo.
    Blanco, Clara
    Instituto Nacional del Carbón (CSIC), Oviedo.
    Santamaria, Ricardo
    Instituto Nacional del Carbón (CSIC), Oviedo.
    Lundblad, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Reaction Engineering.
    Björnbom, Pehr
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Reaction Engineering.
    An insight into Faradaic phenomena in activated carbon investigated by means of the microelectrode technique2007In: Electrochemistry communications, ISSN 1388-2481, E-ISSN 1873-1902, Vol. 9, no 9, p. 2320-2324Article in journal (Refereed)
    Abstract [en]

    Cyclic voltammetry was performed on activated carbon particles in a microelectrode setup to investigate the behaviour of an activated carbon with oxygen functionalities. Quinoid type redox peaks were clearly seen in the potential region around -0.5 V vs. Hg/HgO. After polarization below -0.4 V, an anodic peak confirms previous studies using a pristine carbon, but in the present work much higher in intensity. In addition, a corresponding cathodic peak, not previously reported, was also found. The appearance of this pair of peaks in a functionalized carbon may be connected to reversible hydrogen adsorption together with Faradaic reactions involving oxygenated functional groups.

  • 20.
    Malmberg, Helena
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Reaction Engineering.
    Zuleta, Marcelo
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Reaction Engineering.
    Lundblad, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Reaction Engineering.
    Björnbom, Pehr
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Reaction Engineering.
    Ionic transport in pores in activated carbons for EDLCs2006In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 153, no 10, p. A1914-A1921Article in journal (Refereed)
    Abstract [en]

    The transport properties and morphology of an activated carbon containing macro-, meso-, and micropores were studied and compared to a sophisticated fully nanoporous carbon that almost lacks meso- and macropores. The morphology of the activated carbon was studied using nitrogen adsorption methods and the pore size distribution was investigated using Barret, Joyner, and Halenda and density functional theory models. The transport properties were studied using a microelectrode technique that allows for determination of the effective diffusivity, D-eff. For the meso/macroporous carbon the effective diffusivity was determined using potential step experiments and analysis for both Cottrell and filling diffusivities were made. The Cottrell diffusivity was smaller than the value of the filling diffusivity, with mean values of (9.4 +/- 3.8) x 10(-14) m(2) s(-1) and (3.1 +/- 1.6) x 10(-12) m(2) s(-1), respectively. This difference in diffusivities is the basis for an agglomerate hypothesis presented for the meso/macroporous carbon. The results for the meso/macroporous carbon are compared with the corresponding results for the sophisticated fully nanoporous carbon. This gave further evidence for the presented agglomerate hypothesis.

  • 21.
    Risberg, Per
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Johansson, David
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Andrae, Johan
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Kalghatgi, Gautam
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Björnbom, Pehr
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    The Influence of NO on the Combustion Phasing in an HCCI Engine2006In: SAE 2006 World Congress & Exhibition Technical Papers, 2006, no 2006-01-0416Conference paper (Refereed)
    Abstract [en]

    In this work the influence of NO on combustion phasing has been studied experimentally in a single cylinder HCCI engine. A isooctane/n-heptane blend (PRF), a toluene/n-heptane mixture (TRF) and a full boiling range gasoline were tested at two different operating conditions with NO concentrations ranging from 4 up to 476 ppm in the fresh intake air. All three fuels had the same RON of 84. The first operating condition had a high intake pressure (2 bar absolute) and low intake temperature (40 °C), where low temperature chemistry is relatively prominent. The other operating condition had a high intake temperature (100 °C) and atmospheric intake pressure with significantly lower cool flame reactivity. Additionally the effect of NO at two different engine speeds, 900 and 1200 rpm were studied.

    The combustion phasing, represented by CA50 was advanced up to 12.5 CAD by the influence of NO. In the cases with the TRF and the full boiling range gasoline the combustion phasing advanced with an increasing NO concentration. The combustion phasing in the PRF case also advanced at low concentrations of NO, but retarded beyond the baseline case at high concentrations in the high-pressure case. Such effects on combustion phasing are explained in terms of reaction kinetic theory from the literature. At low concentrations NO provides extra branching pathways, but as NO concentration increases termination reactions take over. The interaction of NO and aromatic fuels has not been theoretically examined to the same extent in the literature and more work in this area is needed.

  • 22.
    Ruiz, Vanesa
    et al.
    Instituto Nacional del Carbón, CSIC, Oviedo.
    Malmberg, Helena
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Blanco, Clara
    Instituto Nacional del Carbón, CSIC, Oviedo.
    Lundblad, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Björnbom, Pehr
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Santamaría, Ricardo
    Instituto Nacional del Carbón, CSIC, Oviedo.
    A study of Faradaic phenomena in activated carbon by means of macroelectrodes and single particle electrodes2008In: Journal of Electroanalytical Chemistry, ISSN 0022-0728, E-ISSN 1873-2569, Vol. 618, no 1-2, p. 33-38Article in journal (Refereed)
    Abstract [en]

    The electrochemical behaviour of a chemically activated carbon with oxygen-containing surface groups was studied using a conventional macroelectrode configuration with disc electrodes and the single particle microelectrode technique. The results of both experimental set-ups were compare taking into account the visible peaks of the surface groups, capacitance and Faradaic currents. Galvanostatic cycling and cyclic voltammetry performed at different potential windows clearly indicated that the microelectrode configuration was more sensitive to Faradic phenomena (i.e. oxygenated functional groups). The incorporation of mainly CO2-evolving groups after positive polarization may cause the degradation of the carbon material, leading to a distortion in its capacitive behaviour as a result of a restriction of the available surface area.

  • 23.
    Zuleta, Marcelo
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Björnbom, Pehr
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Lundblad, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Characterization of the electrochemical and ion-transport properties of a nanoporous carbon at negative polarization by the single-particle method2006In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 153, no 1, p. A48-A57Article in journal (Refereed)
    Abstract [en]

    In this work, the electrochemical processes occurring in a nanoporous carbon, obtained from silicon carbide and used as negative electrode material for supercapacitors, have been investigated by means of the single-particle microelectrode method. The processes studied deal with hydrogen adsorption, evolution, and oxidation using 6 M KOH as electrolyte. It was found that adsorption of hydrogen started at -0.5 V, hydrogen evolution at -1.4 V vs Hg vertical bar HgO, and that hydrogen oxidation occurs in two steps. The first oxidation process takes place between 0 and 0.1 V, shown by a well-defined current peak on the voltammograms. The second oxidation stage occurs between 0.1 and 0.5 V, indicated by a successive increase in current with the number of cycles. It was also found that after the first oxidation process, subsequent cycling between -0.5 and -1 V leads to a larger accumulation of hydrogen inside the nanopores and to a decrease of the effective diffusion coefficient (D-eff) of potassium ions. Subsequent oxidation, in a second process, leads to a total consumption of hydrogen and to an increase of D-eff.

  • 24.
    Zuleta, Marcelo
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Björnbom, Pehr
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Lundblad, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Effects of pore surface oxidation on electrochemical and mass-transport properties of nanoporous carbon2005In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 152, no 2, p. A270-A276Article in journal (Refereed)
    Abstract [en]

    A new nanoporous (NP) carbon material with a high surface area and a narrow pore size distribution, around 8 A, has been used to investigate the effects that electrochemical oxidation at positive potentials exerts on the capacitance values and effective diffusion coefficients of ions inside the nanopores. An electroanalytical method, based on the single-particle microelectrode technique with micromanipulator, was applied to calculate the diffusion coefficients of 6 M KOH ions in NP carbon. The results were analyzed for short times using the Cottrell model and for long times using the spherical diffusion model. Using cyclic voltammetry, was found that different stages of oxidation took place between 0 and 0.5 V vs. Hg\HgO. After repeated cycling in the first region of oxidation (0-0.3 V), an activation leading to higher capacitance was observed, but the diffusion coefficients decreased from approximately 2 x 10(-9) to 0.5 x 10(-10) cm(2) s(-1). In the second region of oxidation (0.3-0.5 V), where CO2 and 02 evolution can occur, both the capacitance and the diffusion coefficients decreased more dramatically. The effective diffusion coefficients of ions of an activated carbon particle were dependent on the operation potential; decreasing by an order of magnitude when going from -0.3 to +0.3 V. The results are discussed in terms of chemisorption of small oxygen functional groups (-OH or C=O) and ionic interaction with the pore wall.

  • 25.
    Zuleta, Marcelo
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Björnbom, Pehr
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Lundblad, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Nurk, G.
    Kasuk, H.
    Lust, E.
    Determination of diffusion coefficients of BF4- inside carbon nanopores using the single particle microelectrode technique2006In: Journal of Electroanalytical Chemistry, ISSN 0022-0728, E-ISSN 1873-2569, Vol. 586, no 2, p. 247-259Article in journal (Refereed)
    Abstract [en]

    The electrochemical and mass transport properties of TEABF(4) in a nanoporous (NP) carbon material, obtained from silicon carbide, was studied using single particles and a microelectrode technique. The carbon particles of size 100-200 mu m were studied by cyclic voltammetry and potential step measurements. The effective diffusion coefficients (D-eff) were calculated starting from the asymptotic solutions of Fick's second law for short and long time regions. The results show that cycling at low sweep rates was needed in order for the electrolyte to penetrate the inner porosity of the particles. The carbon material showed different electrochemical and mass transport properties depending on the applied potential. At negative polarisation, the results suggest that TEA(+) was adsorbed on the pore wall, however, being transported very slowly inside the pores. The average D-eff after cycling at both positive and negative potentials was 1.1(+/- 0.4) x 10(-8) cm(2) s(-1), using the Cottrell relation and 1.5(+/- 0.6) x 10(-8) cm(2) s(-1), using the radial diffusion solution. The average value of D-eff after cycling at negative potentials was 1.7(+/- 0.6) x 10(-8) cm(2) s(-1) using both mathematical solutions.

  • 26.
    Zuleta, Marcelo
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Bursell, Martin
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Björnbom, Pehr
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Lundblad, Anders
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Determination of the effective diffusion coefficient of nanoporous carbon by means of a single particle microelectrode technique2003In: Journal of Electroanalytical Chemistry, ISSN 0022-0728, E-ISSN 1873-2569, Vol. 549, p. 101-108Article in journal (Refereed)
    Abstract [en]

    A single particle microelectrode technique with a micromanipulator was applied and adapted for characterisation of mass transport properties of ionic species in a high surface area nanoporous carbon, with uniform pore size of 8 Angstrom. The effective diffusivity of 6 M KOH in this material was determined by means of potential step experiments on nanoporous carbon particles of different sizes. The results were analysed for short times (Cottrell model) and for long times (spherical diffusion model). The average effective diffusion coefficient for short and long times was 1.5x10(-9) and 1.2x10(-9) cm(2) s(-1), respectively. The relatively small diffusivity values are discussed in terms of interaction between the ion hydration shell and water molecules adsorbed on the pore wall.

1 - 26 of 26
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