Ändra sökning
Avgränsa sökresultatet
12 51 - 81 av 81
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Träffar per sida
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
Markera
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 51.
    Reifarth, Simon
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Tillmark, Nils
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Exergy and Energy Analysis of HP and LP EGR-systemArtikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    The emission legislation throughout the world is getting moreand more stringent. Especially in the US and Europe, dieselengine manufacturers are facing big challenges in order tokeep their engine emissions within the limits. In addition totraditional legislation of harmful emissions, the emission ofCO2, i.e. the fuel consumption, is starting to be subject of newlegislation. Many measures that control the harmful emissionscounteract the reduction of fuel consumption. After treatmentsystems for example increase backpressure, thus lowering theengine efficiency.Exhaust gas recirculation (EGR) is an important tool foremission control in modern diesel engines. The EGR-loopinduces some pumping losses thus decreasing the overallengine efficiency. Many studies have been published that aimat minimizing these losses. The use of a low-pressure EGRloop is one of the most common ways to alternate the system.This study compares a low-pressure (LP) and a high-pressureHP) EGR-system with focus on single components.To analyze the gas exchange system, both energy and exergybalance methods can be used. In this study, both methods arecompared and specific advantages and disadvantages areshown. It is shown that the exergy analysis contains usefulinformation for engine development regarding the efficiencyof single components and their influence on the entire systems performance.

  • 52.
    Reifarth, Simon
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Transient EGR in a High-Speed DI Diesel Engine for a set of different EGR-routings2010Ingår i: SAE International Journal of Engines, ISSN 1946-3936, Vol. 3, nr 1, s. 1071-1078Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    EGR has been proven to reduce NOx emissions from diesel engines significantly and is nowadays widely used in production engines. To reach future emission legislation standards, alternative EGR-routings that deliver higher EGR- rates get into the focus of researchers. As the steady-state emissions are reduced more and more, the emission peaks in transient parts of driving cycles gain importance. Therefore it is interesting to analyze the transient behavior of different EGR-routings. In this work, a 1-D simulation is performed in GT-Power for a 1.9 liter passenger car diesel engine equipped with cooled short-route EGR and a variable geometry turbine. For calibration of the simulation, load transients are measured including the measurement of transient EGR-rates using a fast CO2-analyzer and cylinder pressure to obtain heat-release data. A database with heat-release rates for transient combustion is collected to enable the simulation to run with real combustion data at all points of the transients. The transient EGR-rate as well as the intake pressure are used as criteria to chose the right heat-release rate for a certain cycle. A set of different ways of supplying EGR, namely hybrid EGR, pump-assisted EGR and a reed valve in the EGR- circuit are then implemented in the simulation software and analyzed with respect to transient response and fuel consumption. Another aspect of the analysis is the possibility to control the EGR-rate during the transient. This includes positive load transients with EGR-shutoff as well as negative load transients with need for fast EGR-delivery.

  • 53.
    Reifarth, Simon
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    TRANSIENT EGR IN A LONG-ROUTE AND SHORT-ROUTE EGR-SYSTEM2009Ingår i: PROCEEDINGS OF THE 2009 SPRING TECHNICAL CONFERENCE OF THE ASME INTERNAL COMBUSTION ENGINE DIVISION, NEW YORK: AMER SOC MECHANICAL ENGINEERS , 2009, s. 761-770Konferensbidrag (Refereegranskat)
    Abstract [en]

    The use of EGR to lower NOx-emissions from Diesel engines is a well-documented method. Recently, more and more research is done on alternative EGR routing systems such as long-route EGR. To reach future emission legislation goals it is not sufficient to focus on steady-state driving. The emission peaks during the transient parts of driving cycles are gaining importance. It is therefore interesting to analyze the EGR-flow in transients for different configurations of the EGR system. In this work, a 1-D simulation is performed in GT-Power for a Euro 4 passenger car diesel engine equipped with cooled short-route EGR and a variable geometry turbine. For calibration of the simulation, load transients were measured including the measurement of transient EGR-rates using a fast CO2-analyzer and cylinder pressure to obtain heat-release data. While the transient heat-release rates are used as an input for the combustion-simulation, the EGR response measurements are used as a reference for calibration of the EGR-system and its components. A long route EGR system and a short-route EGR system are then simulated and compared, focusing on transient response, availability of EGR during the transient and the fuel consumption in steady state. It is shown that the long-route system has advantages in both steady-state and transient driving conditions. In steady state it can decrease fuel consumption, in transient it can provide EGR without negative effect on the transient response.

  • 54.
    Renberg, Ulrica
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Westin, Fredrik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.). KTH, Skolan för industriell teknik och management (ITM), Centra, Centrum för förbränningsteknik, CICERO (stängd 20101231).
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Fuchs, Laszlo
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik.
    Study of Junctions in 1-D & 3-D Simulation for Steady and Unsteady Flow2010Ingår i: SAE technical paper series, ISSN 0148-7191, nr 01-1050Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work a comparative study between 1-D and 3-D calculations has been performed on different junctions. The geometries are a 90° T-junction with an area ratio of unity and a 45° junction with an area ratio of 1.78 between the main pipe and the side branch. The latter case had an offset between the centerlines of the main and the branched pipe. The 3-D modeling framework uses the Reynolds Averaged Navier-Stokes (RANS) equations with the k-ε model both for the steady and the unsteady flow cases. The comparison is made both under steady and pulsating flow conditions. The aim has been to assess the 1-D/3-D differences in terms of measures for flow losses.

    There are large discrepancies between the 1-D and 3-D computed losses in junctions. The relative differences between 1-D and 3-D computed losses in isentropic power are 63 % and 175 % for the 90° and the 45 ° junctions without including the losses in downstream pipe legs. These figures are reduced to 12 % and 114 % respectively when including a straight pipe segment of one diameter downstream of the junction outlets.

    For the 90° junction at pulsating flow, the discrepancy in 1-D and 3-D computed loss is lower compared to the steady flow case if comparing only the losses in the junction, but similar to the steady discrepancy if including the downstream pipe losses. For the 45° junction, the discrepancies are much larger. The 1-D loss is near six times that of the corresponding 3-D value if comparing the losses in the junction alone, and 3 times the 3-D value if including the losses in 10 diameter of the outlet pipe.

  • 55.
    Renberg, Ulrica
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Fuchs, Laszlo
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik.
    A Comparative Study Between 1D and 3D Computational Results for Turbulent Flow in an Exhaust Manifold and in Bent Pipes2009Ingår i: SAE Technical Papers, 2009, nr 01-1112Konferensbidrag (Refereegranskat)
    Abstract [en]

    To improve today’s 1D engine simulation techniques it is important to investigate how well complex geometries such as the manifold are modeled by these engine simulation tools and to identify the inaccuracies that can be attributed to the 1D assumption. Time resolved 1D and 3D calculations have been performed on the turbulent flow through the outer runners of an exhaust manifold of a 2 liter turbocharged SI engine passenger car

    The total pressure drop over the exhaust manifold, computed with the 1D and 3D approach, showed to differ over an exhaust pulse. This is so even though a pressure loss coefficient correction has been employed in the 1D model to account for 3D flow effects.

    The 3D flow in the two outer runners of the manifold shows the presence of secondary flow motion downstream of the first major curvature. The axial velocity profile downstream of the first turn loses its symmetry. As the flow enters the second curvature a swirling motion is formed. This secondary flow motion prevails with considerable strength at the outlet plane, where the two runners join.

    The turbulent flow through single bent pipes with different turning angle as well as a double bent pipe is also computed using both the 1D and the 3D model, the double bent pipe also for time-varying flow. The results are expressed and compared in terms of pressure losses.

    The results show that a comparison between 1D and 3D computed pressure loss through a bent geometry is only reasonable for cases where the downstream portion of the pipe after the bend is long enough. This does not hold for geometries like an engine exhaust manifold.

  • 56.
    Renberg, Ulrica
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Olofsson, Ulf
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Tribologi.
    Instantaneous On-Engine Turbine Efficiency for an SI Engine in the Closed Waste Gate Region for 2 Different Turbochargers2006Ingår i: SAE Technical Papers, 2006, nr 01-3389Konferensbidrag (Refereegranskat)
    Abstract [en]

    1D engine simulations of turbocharged engines are difficult to perform with good accuracy. Calculations of turbine performance are based on performance maps. These are measured under steady flow conditions using air at moderate temperatures, not very representative of the very hot and pulsating gas flow the on-engine turbine is exposed to. To improve the predictivity of today's 1D engine calculations or the limiting factors of the turbocharger itself, it is most important to gain deeper understanding of how the turbine behaves under on-engine conditions.

    The objective of this paper is to compare calculated instantaneous on-engine turbine efficiency based on measurements with results from using steady-flow efficiency performance maps. The work is performed using two different turbochargers at two operating points with closed waste gate.

    It is shown that the turbine efficiency characteristic derived from measurements and that from using steady-flow efficiency performance maps describe a quite different behavior of the turbine. The on-engine turbine efficiency has systematically shown to be asymmetric over an exhaust pulse. It is considerably higher during the “downhill side” of the pulse, a phenomenon not captured by the 1D quasi steady calculations.

    An error estimation is made for the measurement-based efficiency. The cumulative error results from individual measurement errors of its constituent parameters. The efficiency uncertainty is most governed and very sensitive to the measurement error of the turbine shaft speed. The pressure before and after the turbine are also important to measure correctly.

  • 57.
    Risberg, Per A.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Adlercreutz, Ludvig
    Gómez Aguilera, Miguel
    Johansson, T.
    Stensiö, Lars
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Development of a heavy duty nozzle coking test2013Ingår i: SAE Technical Papers, 2013, Vol. 11Konferensbidrag (Refereegranskat)
    Abstract [en]

    The diesel engine is still one of the most common and most efficient mobile energy converters. Nevertheless, it is troubled by many problems, one of them being nozzle coking. This is not a new problem; however, due to the introduction of more advanced injection systems and a more diverse fuel matrix, including biofuels, the problem has become more complex. The nozzle holes are also much narrower today than when the problem first appeared and are therefore more sensitive to coking. Two CEC sanctioned coking tests exist for diesel engines, but no universally accepted test for heavy duty engines. In this paper, tests have been performed with B10 doped with 1 ppm zinc on a single cylinder engine, based on a heavy duty engine, with the purpose to develop a simple accelerated coking test. To have relevance to real usage, the test was based on real engine load points from a high power Euro V engine calibration. The coking propensity was studied in an engine speed sweep at max load. Based on this, a repeatable, convenient, single load point, 6 hour test with a one hour soak time in the middle, that managed to produce significant coking, was established. The average nozzle temperature was measured to around 255 °C with a thermocouple instrumented injector. Coking was evaluated based on the measured power loss during the tests and validated in a flow rig were the nozzle was disassembled from the injector and the flow was measured separately before and after the coking tests to isolate the effects of nozzle coking. Since the start of the tests are is of major importance, to condition the engine is very important. Running the engine on half load was concluded not to have significant effect on nozzle coking. It was also found that overnight engine soak lead to on average an increase in power output of around 1.2 % and that shorter soak periods did not significantly influence the deposit build up.

  • 58.
    Risberg, Per
    et al.
    KTH, Tidigare Institutioner                               , Maskinkonstruktion.
    Kalghatgi, Gautam
    Ångström, Hans-Erik
    KTH, Tidigare Institutioner                               , Maskinkonstruktion.
    A Method of Defining Ignition Quality of Fuels in HCCI Engines2003Konferensbidrag (Refereegranskat)
    Abstract [en]

    A homogeneous charge compression ignition (HCCI) engine has been run at different operating conditions with fuels of different RON and MON and different chemistries. The ignition quality of the fuel at a given operating condition is characterized by CA50, the crank angle at which the cumulative heat released reaches 50% of the maximum value for the cycle. It is found that CA50 might show no correlation with either RON or MON but correlates very well with the Octane Index, OI defined as OI = (1-K)RON + KMON = RON - KS, where K is a constant depending on the engine operating condition and S is the fuel sensitivity, (RON - MON). The higher the OI, the more the resistance to autoignition and the later is the heat release in the HCCI engine at a given condition. When the engine is run with a boost pressure of 1 bar and with the intake air temperature maintained at 40° C, K is highly negative and fuels of low MON, such as those containing aromatics, olefins or ethanol, have a higher OI and ignite later than paraffinic fuels of comparable RON. When the engine is run with no intake boost and the intake air is heated to 120° C, the value of K becomes slightly greater than zero so that the autoignition quality of the fuel is determined mostly by its RON. Thus K decreases as the engine is run relatively cooler and at higher pressures and MON contributes less to the measure of resistance to autoignition. This trend is in line with earlier studies of autoignition in knocking engines.

  • 59.
    Risberg, Per
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Kalghatgi, Gautam
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Advantages of fuels with high resistance to auto-ignition in late-injection, lowtemperature, compression ignition combustion2006Ingår i: Submitted to SAE Powertrain & Fluid Systems Conference & Exhibition, heldOctober 2006, in Toronto, Ontario, Canada. SAE 2006-01-xxxx, 2006Konferensbidrag (Refereegranskat)
    Abstract [en]

    Oxides of nitrogen (NOx) and smoke can be simultaneously reduced in compression ignition engines by getting combustion to occur at low temperatures and by delaying the heat release till after the fuel and air have been sufficiently mixed. One of the ways to obtain such combustion in modern engines using common-rail direct injection is to inject the fuel near top dead centre with high levels of exhaust gas recirculation (EGR) - Nissan MK style combustion. In this work we study the effect of fuel auto-ignition quality, using four fuels ranging from diesel to gasoline, on such combustion at two inlet pressures and different EGR levels. The experiments are done in a 2 litre single-cylinder engine with a compression ratio of 14 at an engine speed of 1200 RPM. The engine can be easily run on gasoline with a single injection near TDC, even though it cannot be run with very early injection, in the HCCI mode. Moreover for any given condition, gasoline has a significantly higher ignition delay for the same combustion phasing and hence results in very much lower NOx and smoke for a given load compared to diesel fuels. Using gasoline, an IMEP of 14.86 bar could be reached with ISFC of 178 g/kWh, smoke < 0.4 FSN, peak pressure of 133 bar, ISNOx of 1.21 g/kWh, and ISHC and ISCO < 4 g/kWh. It was not possible to get comparable performance with diesel fuels with low smoke at the same operating conditions. Further improvements in all these parameters using gasoline should be possible by optimising injector and engine design and operating conditions and bringing in other strategies such as multiple injections.

  • 60.
    Risberg, Per
    et al.
    KTH, Tidigare Institutioner                               , Maskinkonstruktion.
    Kalghatgi, Gautam
    Ångström, Hans-Erik
    KTH, Tidigare Institutioner                               , Maskinkonstruktion.
    Auto-ignition quality of gasoline-like fuels in HCCI engines2003Konferensbidrag (Refereegranskat)
    Abstract [en]

    The auto-ignition quality of a fuel of any chemistry at a given engine condition is described by an octane index defined as, OI = (1-K) RON + K MON, where RON and MON are the Research and Motor Octane numbers respectively and K depends only on the engine design and operating conditions. The higher the OI value, the greater is the resistance to auto-ignition. A single cylinder homogeneous charge compression ignition (HCCI) engine has been run at thirty seven different operating conditions using fuels of different chemistries and different known RON and MON values. At each operating condition CA50, the crank angle for 50% of the total heat release, is established for different fuels and from this the value of K is determined. We take T comp15 , the temperature when the pressure reaches 15 bar during the compression stroke, as a generic engine parameter. K is strongly dependent on and increases with T comp15 and is less strongly dependent on the mixture strength. Surprisingly, there was no significant effect of engine speed on K. A predictive equation for K as a function of T comp15 and the normalized air/fuel ratio, λ is found. At each operating condition there is an ideal fuel with OI = OI 0 such that heat release occurs at top dead center (TDC). OI 0 increases with increasing P maxcomp and T maxcomp the compression pressure and temperature at TDC, and decreases with increasing λ and engine speed. An empirical equation relating OI 0 to these generic engine parameters is found. These predictive equations could also be used to explore control strategies for an HCCI engine running on a fuel of known RON and MON.

  • 61.
    Risberg, Per
    et al.
    KTH, Tidigare Institutioner                               , Maskinkonstruktion.
    Kalghatgi, Gautam
    KTH, Tidigare Institutioner                               , Maskinkonstruktion.
    Ångström, Hans-Erik
    KTH, Tidigare Institutioner                               , Maskinkonstruktion.
    The influence of EGR on auto-ignition quality of gasoline-like fuels in HCCI engines2004Ingår i: SP-1896, 2004Konferensbidrag (Refereegranskat)
    Abstract [en]

    In previous studies it has been shown that the auto-ignition quality of a fuel at a given engine condition can be described by an octane index defined as, OI=(1-K) RON + K MON, where RON and MON characterize the fuel and the K-value depends only on the engine design and operating conditions. It has been shown that the K-value is highly dependent on the pressure and temperature history. Another important parameter is OI 0 , the OI of the fuel which gives heat release centred at top dead center; OI 0 can be considered to be the requirement of the engine. In previous work, empirical relations for both K and OI 0 in terms of in-cylinder pressure and temperature and engine speed and mixture strength were found but the influence of EGR was not considered. Therefore experiments have been done in a single cylinder engine, working in HCCI mode, at different operating conditions including various internal and external EGR rates, using fuels of different chemistries and different known RON and MON values.

  • 62.
    Risberg, Per
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Kalghatgi, Gautam
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Wåhlin, Fredrik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Auto-ignition quality of Diesel-like fuels in HCCI engines2005Ingår i: Presented at SAE Brazil Fuels & Lubricants Meeting, held May 2005, in Rio DeJaneiro, Brazil. SAE 2005-01-2127, SAE Transactions, 2005Konferensbidrag (Refereegranskat)
    Abstract [en]

    In Homogeneous Charge Compression Ignition (HCCI) engines heat release occurs by auto-ignition and hence the fuel auto-ignition quality is very important. The auto-ignition quality of Diesel fuels is conventionally described by the cetane number. Conventional Diesel fuels are involatile compared to gasoline fuels and mixture preparation becomes far more critical in assessing their behaviour in HCCI engines. This paper considers the relationship between auto-ignition behaviour of Diesel-like fuels in a single-cylinder HCCI engine and the fuel cetane number under different mixture preparation strategies.

  • 63.
    Strålin, Per
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Wåhlin, Fredrik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Nordin, Niklas
    SCANIA CV AB .
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    A Lagrangian Collision Model Applied to an Impinging Spray Nozzle2006Ingår i: Conference paper, SAE Powertrain and Fluid Systems Conference, 2006Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper describes the implementation and evaluation of a collision model for CFD spray simulations. The collision model is intended to be used for prediction of fuel sprays from specially designed impinging spray nozzles.

    The new model is enhanced in terms of collision frequency, post-collisional characteristics and collision induced break-up. The model is evaluated in terms of macro scale properties, such as spray penetration and spray cone angle.

  • 64.
    Strålin, Per
    et al.
    SCANIA CV AB/KTH .
    Wåhlin, Fredrik
    SCANIA CV AB/KTH .
    Ångström, Hans-Erik
    KTH, Tidigare Institutioner                               , Maskinkonstruktion.
    Effects of Injection Timing on the Conditions at Top Dead Center for Direct Injected HCCI2003Konferensbidrag (Refereegranskat)
    Abstract [en]

    A numerical approach has been applied to investigate direct injected HCCI combustion in terms of estimating the conditions at Top Dead Center (TDC) for three different injection timings during a calculated compression stroke in the commercial CFD software FIRE.

    The paper first describes reproduction of the initial spray, which is introduced at different angles during the calculated compression stroke. These spray shapes have been validated by comparison to experimental investigations in a pressurized constant volume vessel with densities in accordance with the cylinder conditions. The sprays origins from a colliding flow nozzle, which is of interest in direct injected HCCI because of increased spray dispersion and turbulence.

    In the calculated compression stroke two fuels were compared: n-dodecane and n-heptane. The injected amount of fuel, 117 mg, results in a generally lean distribution at TDC. For early injection the spray is distributed more homogenously with values close to the overall equivalence ratio which is attractive for direct injected HCCI. When the fuel is injected later approaching TDC, a distribution with both lean and relatively rich fractions appears. These rich fractions are most likely to produce NOx.

  • 65. Westin, Fredrik
    et al.
    Elmqvist, Christel
    Ångström, Hans-Erik
    Correlation between engine simulations and measured data: experiences gained with 1D-simulations of turbocharged SI-enginesManuskript (Övrigt vetenskapligt)
  • 66.
    Westin, Fredrik
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Maskinkonstruktion (Avd.).
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Maskinkonstruktion (Avd.).
    Calculation accuracy of pulsating flow through the turbine of si-engine turbochargers: Part 1 calculations for choice of turbines with different flow characteristics2005Konferensbidrag (Refereegranskat)
    Abstract [en]

    The paper treats pulsating flow through the turbine of SI-engine turbochargers. In engine design, 1D engine-simulations are very convenient tools for optimization and concept studies. However, they have drawbacks in certain areas. The accuracy, when predicting turbocharger turbine power, is lower than desired. The reason for that is a lack of knowledge about the phenomenon of pulsating flow through the turbine. The background to the problem is described in the paper. This investigation aims at learning more about this unsteady, pulsating flow, on the engine. The method used is to do large parameter changes to several parameters in turbine and manifold designs such as A/R and trim in the turbine and also volume and length of the exhaust manifold. For selection of A/R and trim, as well as an aid in the analysis of measured data, the meanline turbine design software Rital from Concepts NREC [1] was used. Three different turbines were investigated, all with the same mass flow capacity. The three different manifolds were designed to alter the pulsation shape at the turbine inlet. The calculation results show, that through these large parameter changes, it is possible to significantly alter the conditions at both the turbine inlet (shape of pressure and massflow curves) and at the turbine wheel inlet (flow angle and velocity). This has a significant impact on the performance of the turbine and engine.

  • 67.
    Westin, Fredrik
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Maskinkonstruktion (Avd.).
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Maskinkonstruktion (Avd.).
    Calculation accuracy of pulsating flow through the turbine of SI-engine turbochargers: Part 2 measurements, simulation correlations and conclusions2005Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper is a continuation of SAE-Paper 2005-01-0222 presented at the 2005 SAE World Congress, denoted Part 1 in this text. In Part 1 three turbines were selected from calculations and three manifolds with different geometries were designed. This paper, Part 2, covers the results from engine-simulations and measurements on these nine different combinations of turbines and manifolds. It was shown that the possibility of maintaining isentropic power was the most important property, overshadowing any differences in turbine efficiency. The isentropic power was inversely dependent on both manifold volume and turbine throat area. The GT-Power models of all nine setups were calibrated against the measured data. The need for efficiency and massflow multipliers is described. The efficiency multiplier depended on mass flow through the turbine, with a distinct minimum value (0.7-0.8) around 0.03 kg/s and higher around that. The efficiency multiplier could not be shown to depend on pulsation amplitude of the turbine inlet flow. The mass flow multiplier was almost linear with engine speed. The on-engine turbine efficiency was calculated from a combination of measured and simulated data. Different approaches for this calculation were tested, among which also mass storage was included. The chosen method used equal massflow in and out from the turbine at every instant and a floating average over 30 CAD. To enable explanation of the different behaviors on the engine, detailed measurements were conducted on the three turbines in a steady-state turbine flow rig. These measurements were used to calibrate separate turbine simulation models in the software Rital, which were used to describe the internal flow of the turbines. The three methods of estimating the on-engine turbine efficiency were compared. GT-Power and Rital showed similar trends for the efficiency, but the on-engine measured efficiency gave lower values for the first, most energetic, part of the exhaust pulse. Furthermore, the three manifold types were analyzed and the benefits from each of them sorted out.

  • 68.
    Westin, Fredrik
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Maskinkonstruktion (Avd.).
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Maskinkonstruktion (Avd.).
    Optimization of turbocharged engines' transient response with application on a formula SAE / Student engine2005Ingår i: SAE Technical Papers, ISSN 0148-7191Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this study, the transient response of a turbocharged engine is minimized by using 1D engine simulation. A method is developed where sequential fractional factorial designs are utilized to first determine the relative importance between a wide range of design parameters and then successively come closer to an optimal setup for minimized transient response. This methodology is first developed and applied to a 2-liter standard production car engine and then it is used for optimization of the 2004 KTH Racing Formula Student engine. The race engine was first designed entirely by using steady-state 1D simulations. These simulations are described and the design explained. The philosophy behind turbocharger selection, manifold tuning etc. is described in detail. After the initial design the engine was optimized for transient response. Measurement data from steady state measurements on the dynamometer is showed for verification as well as pressure data logged in the car on the racetrack.

  • 69.
    Westin, Fredrik
    et al.
    KTH, Tidigare Institutioner, Maskinkonstruktion.
    Ångström, Hans-Erik
    KTH, Tidigare Institutioner, Maskinkonstruktion.
    Rosenqvist, J.
    Heat losses from the turbine of a turbocharged SI-engine - Measurements and simulation2004Konferensbidrag (Refereegranskat)
    Abstract [en]

    Traditionally, heat losses from the turbine are neglected in turbomatching calculations as well as in engine simulations [1]. On the SI-engine, with it's high exhaust temperatures, this assumption will lead to errors in the calculations. Significant amounts of heat are dissipated from the turbine through several mechanisms. This paper contains measurements of the different heat loss mechanisms from the turbine during full load operation on a 4-cylinder SI-engine. The largest loss components are convective and radiative. The heat losses to cooling water and lubrication oil were approximately 3-5% of the total heat loss from the turbine. In addition to heat losses to the surroundings, heat flux is also present internally in the turbocharger. Heat flux from the turbine to the compressor can deteriorate the efficiency of the compressor. Measurements and calculations were performed for several heat flux conditions and it could be concluded that little possibility exists for significant heat flux through the rotor, instead the major heat flux comes from conduction in the housings and external radiation. With the heat transfer included in the model the turbine outlet temperature could be simulated very close to measured. However, incorporation of the heat losses in the simulation did not do very much for the necessity of using correction factors for the turbine efficiency.

  • 70.
    Westlund, Anders
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Lindström, Mikael
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    A 1-D Model for Heat Release Rate and Emission Formation in Diesel Engines Based on Correlations for Entrainment Rate, Lift-Off Length and Ignition Delay: Validation for Transient ConditionsArtikel i tidskrift (Övrigt vetenskapligt)
  • 71.
    Westlund, Anders
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Lindström, Mikael
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    A one-dimensional model for heat release rate and emission formation in diesel engines based on correlations for entrainment rate, lift-off length and ignition delay: Validation for transient conditions2012Ingår i: Proceedings of the Institution of mechanical engineers. Part D, journal of automobile engineering, ISSN 0954-4070, E-ISSN 2041-2991, Vol. 226, nr D9, s. 1243-1258Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A simplified one-dimensional model for combustion and emission formation in diesel engines has been developed in a project where the long-term objective is to predict the emissions during transient operation. The models are intended to be used as a tool for pre-development of after-treatment systems and for offline calibration of engine controls. These applications imply that the final model must be both computationally inexpensive and comprehensive. The model is based on a correlation for the air entrainment rate which is applied to a discretized injection event. On this, the combustion rate and the emission formation rate are imposed with simple models. In this publication, the model is validated for the targeted conditions and transient operation. The model is based on a previously presented model which was evaluated for steady state conditions. The model presented here has been modified to address the shortcomings that were identified in the previous evaluation. The model was able to predict the heat release rate and the emissions of nitrogen oxide ( NO) and soot with reasonable accuracy and also the requirement regarding the computational time was met. The average time for simulation of one engine cycle was approximately 3 s on a standard laptop.

  • 72.
    Westlund, Anders
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Centra, Centrum för förbränningsteknik, CICERO.
    Winkler, Niklas
    KTH, Skolan för industriell teknik och management (ITM), Centra, Centrum för förbränningsteknik, CICERO.
    Diotallevi, Fabrizio
    KTH, Skolan för industriell teknik och management (ITM), Centra, Centrum för förbränningsteknik, CICERO.
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Centra, Centrum för förbränningsteknik, CICERO.
    Predictions and Measurements of Transient NO Emissions for a Two-stage Turbocharged HD Diesel Engine with EGR2008Ingår i: Proceedings THIESEL 2008 Conference on Thermo-and Fluid Dynamic Processes in Diesel Engines, 2008Konferensbidrag (Refereegranskat)
  • 73.
    Westlund, Anders
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Centra, Centrum för förbränningsteknik, CICERO.
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Centra, Centrum för förbränningsteknik, CICERO.
    Evaluation of Techniques for Transient PM-Measurements2008Ingår i: SAE Papers 2008-01-1680, SAE International , 2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    PM-emissions during a load transient have been measured regarding particle mass, exhaust transparency and particle number concentrations in different size ranges. The load transient was from low to medium load at constant speed and was performed with a single cylinder research engine. Mass measurements were conducted with a Tapered Element Oscillating Microbalance . Exhaust transparency was measured with an Opacimeter. Particle Number Concentrations were measured with two different Condensation Particle Counters , CPCs, where one of them was equipped with a Particle Size Selector , PSS, in order to distinguish accumulation mode particles from nucleation mode. An Engine Exhaust Particle Sizer , EEPS, was also used in parallel with the CPCs and provided a full size distribution. For dilution, a rotating disc diluter and a two stage ejector diluter was used. In total two stages of hot dilution and one unheated. It was found that all instruments, except the TEOM, had acceptable time resolution for dynamic measurements with the dilution and acquisition setup used in this experiment. In most aspects, the measurements from the different instruments were consistent and the discrepancies could be explained by their measuring principles. In some cases, simultaneous use of different instruments could provide a more detailed description of the emitted PM. It was also concluded that the rotating disc diluter, with some reservations, could be used for transient measurements.

  • 74.
    Westlund, Anders
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Centra, Centrum för förbränningsteknik, CICERO (stängd 20101231).
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Centra, Centrum för förbränningsteknik, CICERO (stängd 20101231).
    Fast Physical Emission Predictions for Off-line Calibration of Transient Control Strategies2009Ingår i: SAE Papers 2009-01-1778, SAE International , 2009Konferensbidrag (Refereegranskat)
    Abstract [en]

    A clear trend in engine development is that the engines are becoming more and more complex both regarding components and component-systems as well as controlling them. These complex engines have great potential to minimize emissions but they also have a great number of combinations of setting. Systematic testing to find these optimum settings is getting more and more challenging. A possible remedy is to roughly optimize these settings offline with predictive models and then only perform the fine tuning in the engine test bed. To be able to do so, two things are needed; firstly a engine model that will predict how the different setting affect engine performance and secondly how the engine performance affects the emissions.

  • 75.
    Westlund, Anders
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Centra, Centrum för förbränningsteknik, CICERO (stängd 20101231).
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Centra, Centrum för förbränningsteknik, CICERO (stängd 20101231).
    Fast Physical Prediction of NO and Soot in Diesel Engines2009Ingår i: SAE Papers 2009-01-1121, SAE International , 2009Konferensbidrag (Refereegranskat)
    Abstract [en]

    A clear trend in engine development is that the engines are becoming more and more complex both regarding components and component-systems as well as controlling them. These complex engines have great potential to minimize emissions but they also have a great number of combinations of setting. Systematic testing to find these optimum settings is getting more and more challenging. A possible remedy is to roughly optimize these settings offline with predictive models and then only perform the fine tuning in the engine test bed. To be able to do so, two things are needed; firstly a engine model that will predict how the different setting affect engine performance and secondly how the engine performance affects the emissions.

  • 76.
    Westlund, Anders
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Llindström, Mikael
    Validation of a Simplified Model for Combustion and Emission Formation in Diesel Engines Based on Correlations for Spray Penetration and Dispersion, Gas Entrainment into Sprays and Flame Lift-off2010Ingår i: International Powertrains, Fuels & Lubricants Meeting, 2010, nr 01-1494Konferensbidrag (Refereegranskat)
    Abstract [en]

    A simplified combustion and emission formation model for diesel engines has been developed in a project where the long term objective is to predict emissions during transient operation. The intended application implies that the final model must be both computationally inexpensive and comprehensive so that it can be used for optimization of engine control variables when coupled to full-engine simulation software. As starting point, the proposed model uses diesel spray correlations established in combustion vessels regarding spray penetration, dispersion, gas entrainment, ignition and flame lift-off. It has been found that with minor adaption, these correlations are valid also for combustion in an engine. By assuming a fully mixing controlled combustion after ignition and by use of simplified emission models, the correlations have been found useful for predicting trends in engine-out emission with low computational cost. Besides engine-out emissions and pressure analysis, endoscope instrumentation has been used to provide validation data regarding maximum in-cylinder temperature and soot concentration.

  • 77.
    Winkler, Niklas
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Simulations and Measurements of a Two-Stage Turbocharged Heavy-Duty Diesel Engine Including EGR in Transient Operation2008Ingår i: Modeling of SI and Diesel Engines, 2008, 2008Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    To meet future demands with respect to emissions for heavy-duty diesel engines high EGR rates together with an optimized injection system are most likely required. The increase in smoke production associated with EGR, especially during transient operation implies that high boost pressures are needed to at least maintain the air excess ratio. To reach required boost pressure without extending the response time a more advanced turbocharger system than the use of a single turbocharger might be needed. A possible solution is two-stage turbocharger systems.

  • 78.
    Winkler, Niklas
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Study of Measured and Model Based Generated Turbine Performance Maps within a 1D Model of a Heavy-Duty Diesel Engine Operated During Transient Conditions2007Ingår i: Modeling of SI and Diesel Engines, 2007, 2007Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    One-dimensional engine simulation codes are today frequently used for turbocharger matching in stationary engine operation. Due to the turbocharger's slow response, simulation tools that can predict the engine transient performance are desired.

  • 79.
    Winkler, Niklas
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Olofsson, Ulf
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Tribologi.
    Instantaneous On-Engine Twin-Entry Turbine Efficiency Calculations on a Diesel Engine2005Ingår i: Powertrain & Fluid Systems Conference & Exhibition Technical Papers, 2005Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    One-dimensional engine simulation codes are frequently used for engine development where turbine performance is in focus for overall engine performance. Turbocharger performance can today not be accurately simulated without adjustments of the turbine efficiency and mass flow multipliers. In spite of the fact that engine exhausts are dominated by unsteady pulsating flow the performance maps provided by the turbo manufacturers are measured under steady conditions and for a range that does not cover the entire turbine operating range.

  • 80.
    Wåhlin, Fredrik
    et al.
    Scania CV AB.
    Cronhjort, Andreas
    Scania CV AB.
    Olofsson, Ulf
    KTH, Tidigare Institutioner (före 2005), Maskinkonstruktion.
    Ångström, Hans-Erik
    KTH, Tidigare Institutioner (före 2005), Maskinkonstruktion.
    Effect of Injection Pressure and Engine Speed on Air/Fuel Mixing and Emissions in a Pre-Mixed Compression Ignited (PCI) Engine using Diesel Fuel2004Ingår i: 2004 Powertrain & Fluid Systems Conference & Exhibition Technical Papers, 2004, Vol. 01-2989, s. 2004-01-2989-Konferensbidrag (Refereegranskat)
    Abstract [en]

    PCI combustion of diesel fuel was accomplished in a direct-injected heavy-duty single-cylinder research engine. An impinging spray nozzle combined with a shallow bowl piston design offered a short air/fuel mixing time. Low HC and CO emissions were observed compared to fully premixed operation using n-heptane. A method for evaluating the air/fuel mixing process has been established by quantifying the in-cylinder air/fuel heterogeneity with the NOx emission. The results indicate that high injection pressure and engine speed are favorable for a fast mixing process. The injection pressure had a small impact on HC and CO emissions, while the engine speed had a larger impact. There were no correlation between air/fuel mixing time and HC and CO emissions.

  • 81.
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Two-Stroke Engine with Varaible Compression2005Patent (Övrig (populärvetenskap, debatt, mm))
12 51 - 81 av 81
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf