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  • 1.
    Heide, Jakob
    et al.
    KTH.
    Karlsson, Mikael
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Altimira, Mireia
    KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Numerical Analysis of Urea-SCR Sprays under Cross-Flow Conditions2017Inngår i: SAE technical paper series, ISSN 0148-7191, Vol. 2017-March, nr MarchArtikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Selective Catalytic Reduction (SCR) of NOx through injection of Urea-Water-Solution (UWS) into the hot exhaust gas stream is an effective and extensively used strategy in internal combustion engines. Even though actual SCR systems have 95-96% de-NOx efficiency over test cycles, real driving emissions of NOx are a challenge, proving that there is room for improvement. The efficiency of the NOx conversion is highly dependent on the size of UWS droplets and their spatial distribution. These factors are, in turn, mainly determined by the spray characteristics and its interaction with the exhaust gas flow. The main purpose of this study is to numerically investigate the sensitivity to the modelling framework of the evaporation and mixing of the spray upstream of the catalyst. The dynamics of discrete droplets is handled through the Lagrangian Particle Tracking framework, with models that account for droplet breakup and coalescence, turbulence effects, and water evaporation. All simulations have been run in the commercial code Ansys Fluent 16.0. Experimental validation of droplet size distribution is carried out through PDPA measurements. Through the present study we have identified suitable modelling setup that provides accurate results with a competitive computational cost. Results also show the importance of accounting for the effects of evaporation and turbulent fluctuations in the droplet phase.

  • 2.
    Lalit, Manan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Karlsson, Mikael
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Åbom, Mats
    KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    AN ENGINEERING NON-LINEAR MODEL FOR THERMO-ACOUSTIC ENGINES2015Inngår i: PROCEEDINGS OF THE 22ND INTERNATIONAL CONGRESS ON SOUND AND VIBRATION: MAJOR CHALLENGES IN ACOUSTICS, NOISE AND VIBRATION RESEARCH, 2015 / [ed] Crocker, MJ Pawelczyk, M Pedrielli, F Carletti, E Luzzi, S, INT INST ACOUSTICS & VIBRATION , 2015Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A thermoacoustic engine is a device converting thermal energy into high amplitude acoustic waves that can be harvested, for example, to electricity. For the practical application of this technique it is vital to identify optimum design parameters and operating conditions. There are numerous reports and tools based on the application of the well-established linear theory first derived by Rott. This is useful for determining the working frequency and yields a first indication of the amplification potential of a given design, but cannot predict the saturation amplitude that is limited by non-linear loss mechanisms. In this work an engineering approach for estimating the final output power of a device is discussed. It is assumed that the fundamental mode of the device is dominating, neglecting the loss of acoustic energy into the harmonics. The core of the engine (heat exchangers and stack/regenerator) is represented as an amplitude-dependent acoustic two port in the frequency domain. To close the system the duct network and acoustic load are treated similarly as the core; all parts are then connected to form a low-order acoustic network. One major difficulty is to represent the non-linear losses in the duct network. Here they are lumped and matched to available data in the literature. Starting at a moderate amplitude, the model is then iterated until the amplification is balanced with the losses in the system. At this stage of balance, the saturation pressure is obtained and the final output acoustic power to the acoustic load is found. Subsequently, parameter studies such as frequency sweeps and altering of the phase of the incoming pressure waves are carried out, to note their effect on the system efficiency.

  • 3.
    Zhang, Zhe
    et al.
    KTH, Skolan för teknikvetenskap (SCI).
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Karlsson, Mikael
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Katoshevski, D.
    Particle Number Reduction in Automotive Exhausts Using Acoustic Metamaterials2017Inngår i: SAE International Journal of Engines, ISSN 1946-3936, E-ISSN 1946-3944, Vol. 10, nr 4, s. 1566-1572Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Air pollution caused by exhaust particulate matter (PM) from vehicular traffic is a major health issue. Increasingly strict regulations of vehicle emission have been introduced and efforts have been put on both the suppression of particulate formation inside the engine cylinders and the development of after-treatment technologies such as filters. With modern direct injected engines that produce a large number of really small sub-micron particles, the focus has increased even further and now also includes a number count.The problem of calculating particle trajectories in flow ducts like vehicle exhaust systems is challenging but important to further improve the technology. The interaction between particles and oscillating flows may lead to the formation of particle groups (regions where the particle concentration is increased), yielding a possibility of realizing particle agglomeration. The oscillating flow may simply be hydrodynamic or as assumed here: the flow oscillations are created by sound propagation rather than hydrodynamic approaches. An analysis is presented which gives the relationship between the speed of sound, the mean flow velocity and the amplitude of the acoustic particle velocity for particle agglomeration to be feasible. It is shown that it can be achieved if the convective speed of sound is reduced to the same order as the mean flow velocity. It is therefore suggested to use the so-called acoustic metamaterials, which can help control, direct and manipulate sound waves. At this stage a phenomenological 1D model is used for the analysis, which allows the authors to build an understanding of the effect of the sound waves and flow oscillations on particle motion and paves the way for further analysis on particle agglomeration.

  • 4. Zhou, J.
    et al.
    Karlsson, Mikael
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Study of thermoacoustic engine for automotive exhaust waste heat recovery2019Inngår i: SAE technical paper series, ISSN 0148-7191, Vol. 2019-April, nr AprilArtikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, the travelling-wave thermoacoustic engine (TAE) and its application for recovery of waste heat from automotive exhaust systems is investigated. The aim is to give some insight into the potential, but also limitations of the technique for practical applications. This includes packaging, physical boundary conditions as heating and cooling available, but also system perspectives as influence of legislative drive cycles and degree of hybridization. First, the travelling-wave TAE is described as a low-order acoustic network in the frequency domain. Models, including non-linear effects, are set up for every component in the network to describe the propagation and dissipation of acoustic waves. For a TAE with looped structure, the continuity of pressure and volumetric velocity is employed to determine the saturation pressure, as well as the stable operating point. These models are validated against experimental data available in the literature [1]. This is an engine designed for high-temperature application, but is well documented and yields a good reference for the models and to further the understanding of the TAE. Next, an optimized design for a system to be adapted to the operating conditions typical for heavy-duty systems is studied and proposed. No actual physical prototype has been built and verified, but the design is based on, and is of the same efficiency, as machines that have been reported in the literature. The proposed design and the original TAE are then used to discuss the practical implementation for heavy- and light-duty vehicles on a system level. To improve the utilization of the available exhaust waste heat, a configuration of system heat exchangers combining a self-circulating loop with multiple TAE modules is preliminarily studied. Further research for this configuration is needed for practical implementation although current simulation results are encouraging.

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