ABSTRACT Für ein tieferes Verständnis der komplexen Reaktionskette der ottomotorischen Verbrennun... more ABSTRACT Für ein tieferes Verständnis der komplexen Reaktionskette der ottomotorischen Verbrennung bei Direkteinspritzung und Ladungsschichtung ist eine Untersuchung der Teilprozesse mit optischen Messtechniken erforderlich. Für die gleichzeitige Bestimmung von Temperatur- und Konzentrationsfeldern in verdampfenden Sprays bei der Benzindirekteinspritzung wurde an der Universität Erlangen-Nürnberg die Messtechnik der laserinduzierten Fluoreszenz weiterentwickelt. Diese Größen sind essenziell für ein vertieftes Verständnis der komplexen Sprayverbrennungsprozesse und werden in der vorliegenden Arbeit unter dem Aspekt der Nutzung von Biokraftstoffen mit veränderten Stoffeigenschaften im Vergleich zu Benzin diskutiert.
Acetone (CH<sub>3</sub>)<sub>2</sub>CO is a common tracer for laser-induc... more Acetone (CH<sub>3</sub>)<sub>2</sub>CO is a common tracer for laser-induced fluorescence (LIF) to investigate mixture formation processes and temperature fields in combustion applications. Since the fluorescence signal is a function of temperature and pressure, calibration measurements in high pressure and high temperature cells are necessary. However, there is a lack of reliable data of tracer stability at these harsh conditions for technical application. A new method based on the effect of spontaneous Raman scattering is proposed to analyze the thermal stability of the tracer directly in the LIF calibration cell. This is done by analyzing the gas composition regarding educts and products of the reaction. First measurements at IC engine relevant conditions up to 750 K and 30 bar are presented.
ABSTRACT In this study the effects of weak electric fields on laminar premixed Bunsen flames were... more ABSTRACT In this study the effects of weak electric fields on laminar premixed Bunsen flames were studied using planar laser-induced fluorescence (PLIF) of the formaldehyde molecules and the OH-radicals for flame structure characterization. Simultaneously particle image velocimetry (PIV) is applied to determine the changed flow field of the flame when a positively charged electrode is placed over a laminar Bunsen type flame while the burner is grounded. By application of static fields the flame front is pushed towards the burner and is constrained, which can be attributed to the momentum transfer by the ionic wind. For rich flames the ionic wind effect is intensified due to the increase of the charge carriers and larger momentum transfer of positively charged ions to the neutral species. Consequently, a stronger flow deceleration results in the order of 0.8–1.6 m/s in the post-oxidation zone at supply voltages of 6 kV. The ionic wind was maximized for increased flow velocity which is attributed to the increased flame surface and number of charged species. An excitation of the flame with voltage step functions was conducted to study its transient behavior. First flame response was detected at the flame root point with a response time of 2–4 ms, which is an order of magnitude faster than values provided in the literature for the integral flame. This first flame response occurred after the space charge zones were built-up and the main flame response was detected 6 ms after the voltage rising edge in the whole flame.
ABSTRACT Biofuels and alternative fuels are increasingly being blended with conventional gasoline... more ABSTRACT Biofuels and alternative fuels are increasingly being blended with conventional gasoline fuel to decrease overall CO₂ emissions. A promising way to achieve this is the use of DISI (direct-injection spark-ignition) technology. However, depending on temperature, pressure, chemical composition and the spark timing, unwanted pre-ignition may occur. Despite higher compression ratios, this engine knock can be decreased by lowering the mixing temperature. This results from the larger fuel evaporation enthalpy of certain biofuels which provides a non-homogeneous mixture throughout the combustion chamber. This work focuses on estimating the biofuel evaporation rate from absolute local vapor temperature and concentration. Measurements conducted in a high temperature/pressure cell using a multi-hole injector are carried out by applying planar, 2-line, laser-induced fluorescence and phase doppler interferometry. The temperature, vapor mass fraction and the droplet size distribution of the specific fuel can then be calculated. The pure biofuels n-butanol and ethanol are examined and compared with isooctane as a standard model fuel and with a 3-component biofuel mixture. The resulting local temperature distributions are found to be a function of spray momentum, mixture of vapor with entrained gas, as well as a function of fuel evaporation enthalpy and boiling temperature. In different engine conditions, certain physiochemical properties are found to dominate. For moderate operating conditions the high-boiling point components like n-butanol show a strong cooling effect. The 3-component mixture is found to be strongly influenced by a small amount of the high-boiling point n-butanol. At elevated conditions the cooling behavior changes completely. The fuels show a strong dependence on the evaporation enthalpy rather than to their boiling point. Thus, the temperature reduction in the center of the spray plume is a maximum for ethanol. For late injection timing mode, the evaporation enthalpy of the fuels is the dominating thermophysical property for the evaporation rate.
ABSTRACT Für ein tieferes Verständnis der komplexen Reaktionskette der ottomotorischen Verbrennun... more ABSTRACT Für ein tieferes Verständnis der komplexen Reaktionskette der ottomotorischen Verbrennung bei Direkteinspritzung und Ladungsschichtung ist eine Untersuchung der Teilprozesse mit optischen Messtechniken erforderlich. Für die gleichzeitige Bestimmung von Temperatur- und Konzentrationsfeldern in verdampfenden Sprays bei der Benzindirekteinspritzung wurde an der Universität Erlangen-Nürnberg die Messtechnik der laserinduzierten Fluoreszenz weiterentwickelt. Diese Größen sind essenziell für ein vertieftes Verständnis der komplexen Sprayverbrennungsprozesse und werden in der vorliegenden Arbeit unter dem Aspekt der Nutzung von Biokraftstoffen mit veränderten Stoffeigenschaften im Vergleich zu Benzin diskutiert.
Acetone (CH<sub>3</sub>)<sub>2</sub>CO is a common tracer for laser-induc... more Acetone (CH<sub>3</sub>)<sub>2</sub>CO is a common tracer for laser-induced fluorescence (LIF) to investigate mixture formation processes and temperature fields in combustion applications. Since the fluorescence signal is a function of temperature and pressure, calibration measurements in high pressure and high temperature cells are necessary. However, there is a lack of reliable data of tracer stability at these harsh conditions for technical application. A new method based on the effect of spontaneous Raman scattering is proposed to analyze the thermal stability of the tracer directly in the LIF calibration cell. This is done by analyzing the gas composition regarding educts and products of the reaction. First measurements at IC engine relevant conditions up to 750 K and 30 bar are presented.
ABSTRACT In this study the effects of weak electric fields on laminar premixed Bunsen flames were... more ABSTRACT In this study the effects of weak electric fields on laminar premixed Bunsen flames were studied using planar laser-induced fluorescence (PLIF) of the formaldehyde molecules and the OH-radicals for flame structure characterization. Simultaneously particle image velocimetry (PIV) is applied to determine the changed flow field of the flame when a positively charged electrode is placed over a laminar Bunsen type flame while the burner is grounded. By application of static fields the flame front is pushed towards the burner and is constrained, which can be attributed to the momentum transfer by the ionic wind. For rich flames the ionic wind effect is intensified due to the increase of the charge carriers and larger momentum transfer of positively charged ions to the neutral species. Consequently, a stronger flow deceleration results in the order of 0.8–1.6 m/s in the post-oxidation zone at supply voltages of 6 kV. The ionic wind was maximized for increased flow velocity which is attributed to the increased flame surface and number of charged species. An excitation of the flame with voltage step functions was conducted to study its transient behavior. First flame response was detected at the flame root point with a response time of 2–4 ms, which is an order of magnitude faster than values provided in the literature for the integral flame. This first flame response occurred after the space charge zones were built-up and the main flame response was detected 6 ms after the voltage rising edge in the whole flame.
ABSTRACT Biofuels and alternative fuels are increasingly being blended with conventional gasoline... more ABSTRACT Biofuels and alternative fuels are increasingly being blended with conventional gasoline fuel to decrease overall CO₂ emissions. A promising way to achieve this is the use of DISI (direct-injection spark-ignition) technology. However, depending on temperature, pressure, chemical composition and the spark timing, unwanted pre-ignition may occur. Despite higher compression ratios, this engine knock can be decreased by lowering the mixing temperature. This results from the larger fuel evaporation enthalpy of certain biofuels which provides a non-homogeneous mixture throughout the combustion chamber. This work focuses on estimating the biofuel evaporation rate from absolute local vapor temperature and concentration. Measurements conducted in a high temperature/pressure cell using a multi-hole injector are carried out by applying planar, 2-line, laser-induced fluorescence and phase doppler interferometry. The temperature, vapor mass fraction and the droplet size distribution of the specific fuel can then be calculated. The pure biofuels n-butanol and ethanol are examined and compared with isooctane as a standard model fuel and with a 3-component biofuel mixture. The resulting local temperature distributions are found to be a function of spray momentum, mixture of vapor with entrained gas, as well as a function of fuel evaporation enthalpy and boiling temperature. In different engine conditions, certain physiochemical properties are found to dominate. For moderate operating conditions the high-boiling point components like n-butanol show a strong cooling effect. The 3-component mixture is found to be strongly influenced by a small amount of the high-boiling point n-butanol. At elevated conditions the cooling behavior changes completely. The fuels show a strong dependence on the evaporation enthalpy rather than to their boiling point. Thus, the temperature reduction in the center of the spray plume is a maximum for ethanol. For late injection timing mode, the evaporation enthalpy of the fuels is the dominating thermophysical property for the evaporation rate.
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