A new measurement technique was examined for two-dimensional gas-phase temperature and velocity d... more A new measurement technique was examined for two-dimensional gas-phase temperature and velocity determination. Due to the strong influence of the activator and its concentration on the phosphor emission behavior, two phosphor types were investigated (yttrium aluminum garnet doped with dysprosium and yttrium aluminum garnet doped with dysprosium and erbium). Calibration was carried out in a heated air jet. The Dy:YAG and Dy:Er:YAG were tested for the same temperature and gas flow velocities range. Phosphor powder with an average particle size of 2 µm was seeded into the heated air flow where it was excited by two pulsed Nd:YAG lasers operated at wavelengths of 355 nm for laser-induced phosphorescence and 532 nm for particle image velocimetry measurements. The spectral intensity ratio method is applied for thermometry. For the inlet temperatures up to 573 K an average inaccuracy of less than 5% could be obtained. The Dy:Er:YAG showed an improved accuracy and precision due to its increased temperature sensitivity and integral phosphorescence emission. Additionally, for the first time simultaneous singleshot temperature and velocity measurements are presented using thermographic phosphors.
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.
The present study introduces an advanced measurement technique for multi-parameter imaging in opt... more The present study introduces an advanced measurement technique for multi-parameter imaging in optically accessible IC engines which is based on two planar laser-induced fluorescence (PLIF) techniques. A LIF tracer mixture consisting of triethylamine (TEA) and acetone is used to investigate the simultaneous determination of air/fuel-ratio, temperature and exhaust gas/air concentration in a direct-injection spark-ignition (DISI) engine with exhaust gas recirculation (EGR). The approach is based on applying a two-wavelength excitation scheme of acetone for temperature and concentration measurement and employing single-wavelength excitation of TEA for the determination of AFR utilizing the effect of oxygen quenching. At first the spectral properties of the tracer mixture are studied to show the separability of the fluorescence signals of both tracers and to identify possible tracer interactions. For calibration and IC engine measurements the focus is put on the tracer acetone for the determination of temperature and air concentration. Fluorescence calibration at IC engine conditions is conducted with pure acetone and with an acetone/TEA mixture to visualize possible interactions. The tracer mixture is then applied in an optically accessible IC engine for temperature determination, which is compared with results of the commonly used successive application of the two individual techniques. The results suggest the suitability of this measurement technique for the simultaneous determination of air/fuel-ratio, air concentration and temperature in combustion devices like IC engines, which helps in the optimization of mixture formation and the subsequent processes such as ignition and pollutant formation.
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.
The laser-induced fluorescence measurement technique was extended for the simultaneous determinat... more The laser-induced fluorescence measurement technique was extended for the simultaneous determination of temperature and concentration fields in evaporating DISI-sprays (DISI-Direct Injection Spark Ignition). These quantities are essential to gain a deeper understanding of the complex spray combustion processes. This is discussed in the present paper for the application of biofuels with modified fuel properties compared to gasoline.
For the improvement of the phosphorescence emission behavior of phosphor powders for temperature ... more For the improvement of the phosphorescence emission behavior of phosphor powders for temperature measurements in a gas flow, the activator concentration in Dy:YAG was varied and the phosphor was co-doped with the sensitizer erbium (Er). Phosphorescence spectra, overall phosphorescence signal intensities and phosphorescence lifetime were characterized in a furnace up to 1400 K. Planar thermometry was conducted in hot gas flows, whereby an improved average temperature uncertainty of about 3 % was obtained using Dy:YAG and of 1.8 % for Dy:Er:YAG for temperatures of 450 K.
A new measurement technique was examined for two-dimensional gas-phase temperature and velocity d... more A new measurement technique was examined for two-dimensional gas-phase temperature and velocity determination. Due to the strong influence of the activator and its concentration on the phosphor emission behavior, two phosphor types were investigated (yttrium aluminum garnet doped with dysprosium and yttrium aluminum garnet doped with dysprosium and erbium). Calibration was carried out in a heated air jet. The Dy:YAG and Dy:Er:YAG were tested for the same temperature and gas flow velocities range. Phosphor powder with an average particle size of 2 µm was seeded into the heated air flow where it was excited by two pulsed Nd:YAG lasers operated at wavelengths of 355 nm for laser-induced phosphorescence and 532 nm for particle image velocimetry measurements. The spectral intensity ratio method is applied for thermometry. For the inlet temperatures up to 573 K an average inaccuracy of less than 5% could be obtained. The Dy:Er:YAG showed an improved accuracy and precision due to its increased temperature sensitivity and integral phosphorescence emission. Additionally, for the first time simultaneous singleshot temperature and velocity measurements are presented using thermographic phosphors.
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.
The present study introduces an advanced measurement technique for multi-parameter imaging in opt... more The present study introduces an advanced measurement technique for multi-parameter imaging in optically accessible IC engines which is based on two planar laser-induced fluorescence (PLIF) techniques. A LIF tracer mixture consisting of triethylamine (TEA) and acetone is used to investigate the simultaneous determination of air/fuel-ratio, temperature and exhaust gas/air concentration in a direct-injection spark-ignition (DISI) engine with exhaust gas recirculation (EGR). The approach is based on applying a two-wavelength excitation scheme of acetone for temperature and concentration measurement and employing single-wavelength excitation of TEA for the determination of AFR utilizing the effect of oxygen quenching. At first the spectral properties of the tracer mixture are studied to show the separability of the fluorescence signals of both tracers and to identify possible tracer interactions. For calibration and IC engine measurements the focus is put on the tracer acetone for the determination of temperature and air concentration. Fluorescence calibration at IC engine conditions is conducted with pure acetone and with an acetone/TEA mixture to visualize possible interactions. The tracer mixture is then applied in an optically accessible IC engine for temperature determination, which is compared with results of the commonly used successive application of the two individual techniques. The results suggest the suitability of this measurement technique for the simultaneous determination of air/fuel-ratio, air concentration and temperature in combustion devices like IC engines, which helps in the optimization of mixture formation and the subsequent processes such as ignition and pollutant formation.
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.
The laser-induced fluorescence measurement technique was extended for the simultaneous determinat... more The laser-induced fluorescence measurement technique was extended for the simultaneous determination of temperature and concentration fields in evaporating DISI-sprays (DISI-Direct Injection Spark Ignition). These quantities are essential to gain a deeper understanding of the complex spray combustion processes. This is discussed in the present paper for the application of biofuels with modified fuel properties compared to gasoline.
For the improvement of the phosphorescence emission behavior of phosphor powders for temperature ... more For the improvement of the phosphorescence emission behavior of phosphor powders for temperature measurements in a gas flow, the activator concentration in Dy:YAG was varied and the phosphor was co-doped with the sensitizer erbium (Er). Phosphorescence spectra, overall phosphorescence signal intensities and phosphorescence lifetime were characterized in a furnace up to 1400 K. Planar thermometry was conducted in hot gas flows, whereby an improved average temperature uncertainty of about 3 % was obtained using Dy:YAG and of 1.8 % for Dy:Er:YAG for temperatures of 450 K.
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Papers by Lars Zigan