Lars Zigan

Phosphor thermometry in turbulent hot gas flows applying Dy:YAG and Dy:Er:YAG particles

In order to improve 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 the 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.

Characterization of four potential laser-induced fluorescence tracers for diesel engine applications

Four potential laser-induced fluorescence (LIF) tracers, 1-phenyloctane, 1-phenyldecane, 1-methylnaphthalene, and 2-methylnaphthalene, are characterized for diesel engine applications. These tracers, embedded in the diesel primary reference fuels n-C₁₆H₃₄ and iso-C₁₆H₃₄, match the relevant physical properties of commercial diesel fuel much better than the commonly used toluene/iso-octane/n-heptane tracer-fuel system does. The temperature and pressure dependencies of the fluorescence intensities and spectra were measured in a flow cell in nitrogen for each candidate tracer molecule. The results show that the signal intensities of the methylnaphthalenes are about two orders of magnitude higher than for 1-phenyloctane and 1-phenyldecane and show a strong temperature but no pressure, dependence. An analysis of the fluorescence spectrum of 1-methylnaphthalene shows that it also can be used for two-color detection LIF thermometry by choosing appropriate optical filters.

Fuel property and fuel temperature effects on internal nozzle flow, atomization and cyclic spray fluctuations of a direct injection spark ignition–injector

The effect of fuel properties and fuel temperature on the behaviour of the internal nozzle flow, atomization and cyclic spray fluctuations is examined for a three-hole direct injection spark ignition injector by combining numerical simulation of the nozzle flow with macroscopic and microscopic spray visualization techniques. A dominant influence of the liquid fuel viscosity on the highly unsteady, cavitating nozzle flow and spray formation was observed. A reduced viscosity (or larger Reynolds number) increases the flow velocity, turbulence and cavitation in the nozzle and leads to a slim spray with a reduced width but increased spray penetration. Furthermore, the spray cone angle is larger for lower Reynolds numbers due to the changed internal nozzle flow profile as predicted by the numerical calculation. The shot-to-shot fluctuations of the sprays were found to have their origin in the highly unsteady, cavitating nozzle flow. Larger cyclic spray fluctuations were observed at low Reynolds numbers although the predicted vapour formation in the nozzle is weaker. This can be explained by flow instabilities at low Reynolds numbers leading to large fluctuations in the nozzle flow.

Laser sheet dropsizing based on two-dimensional Raman and Mie scattering

The imaging and quantification of droplet sizes in sprays is a challenging task for optical scientists and engineers. Laser sheet dropsizing (LSDS) combines the two-dimensional information of two different optical processes, one that is proportional to the droplet volume and one that depends on the droplet surface, e.g., Mie scattering. Besides Mie scattering, here we use two-dimensional Raman scattering as the volume-dependent measurement technique. Two different calibration strategies are presented and discussed. Two-dimensional droplet size distributions in a spray have been validated in comparison with the results of point-resolved phase Doppler anemometry (PDA) measurements.

Simultaneous two-dimensional measurement of fuel–air ratio and temperature in a direct-injection spark-ignition engine using a new tracer-pair laser-induced fluorescence technique

A planar tracer laser–induced fluorescence technique using a new tracer pair is introduced and has been utilized for the simultaneous detection of the fuel–air ratio and the temperature to characterize mixture formation inside a direct-injection spark-ignition engine. The new tracer pair consists of triethylamine and 3-pentanone, which are simultaneously added to the surrogate fuel isooctane. Triethylamine was used for the determination of the fuel–air ratio. The temperature distribution was evaluated with the two-line excitation laser-induced fluorescence technique using 3-pentanone. Prior to the internal combustion engine measurements, the tracer mixture was first investigated in a flow cell to demonstrate the spectral separability of the fluorescence signals and for the extension of the calibration data basis. As a first application, the tracer pair was applied inside a direct-injection spark-ignition engine operated with a split-injection scheme. For the late second injection, the fuel and temperature stratification was studied during the compression stroke. The measured temperature drop due to evaporative cooling effects was found to be about 100 K in the averaged data and up to 125 K in the single-shot measurements. The relation between fuel-rich areas and strong temperature drop can clearly be seen in the results. Furthermore, the suitability of the tracer pair to resolve cyclic variations is visualized.

Investigation of the chemical stability of the laser-induced fluorescence tracers acetone, diethylketone, and toluene under IC engine conditions using Raman spectroscopy

This paper reports on an investigation of the chemical stability of the common laser-induced fluorescence (LIF) tracers acetone, diethylketone, and toluene. Stability is analyzed using linear Raman spectroscopy inside a heated pressure cell with optical access, which is used for the LIF calibration of these tracers. The measurements examine the influence of temperature, pressure, and residence time on tracer oxidation, which occurs without a rise in temperature or pressure inside the cell, highlighting the need for optical detection. A comparison between the three different tracers shows large differences, with diethylketone having the lowest and toluene by far the highest stability. An analysis of the sensitivity of the measurement shows that the detection limit of the oxidized tracer is well below 3% molar fraction, which is typical for LIF applications in combustion devices such as internal combustion (IC) engines. Furthermore, the effect on the LIF signal intensity is examined in an isothermal turbulent mixing study.

Application of linear Raman spectroscopy for the determination of acetone decomposition

Acetone (CH3)2CO 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.

Fluorescence characteristics of the fuel tracers triethylamine and trimethylamine for the investigation of fuel distribution in internal combustion engines.

Laser-induced fluorescence based on fuel tracers like amines is a suitable measurement technique for mixing studies in internal combustion (IC) engines. Triethylamine has often been used in gasoline IC engines; however, no detailed fluorescence characterization for excitation at 263 or 266 nm is available. Trimethylamine (TMA) exhibits high potential as a gaseous fuel tracer but little information about TMA fluorescence is currently available. A picosecond laser source combined with a streak camera equipped with a spectrograph was used to determine the spectral fluorescence emission and fluorescence decay time of both tracers. The tracers were investigated at various temperatures and pressures in a calibration cell with nitrogen as bath gas. The results provide an in-depth understanding of the fluorescence characteristics of both tracers and allow assessment of their application to the investigation of fuel distribution in IC engines.

Fuel concentration imaging inside an optically accessible diesel engine using 1-methylnaphthalene planar laser-induced fluorescence

The performance and emissions of modern automotive diesel engines are highly dependent on the application of pilot injection technology. This technology also appears well suited for application to low-temperature combustion strategies. In this study, the first results of a new quantitative planar laser-induced fluorescence equivalence ratio measurement technique of pilot injections inside an optically accessible diesel engine are presented using 1-methylnaphthalene as a tracer in a mixture of the diesel primary reference fuels, n-hexadecane (cetane) and 2,2,4,4,6,8,8-heptamethylnonane (iso-cetane). This combination overcomes the shortcomings of mismatched fuel volatility and density associated with commonly used toluene/n-heptane/iso-octane planar laser-induced fluorescence techniques. A tracer characterization in a flow cell and a calibration in the internal combustion engine are performed. The internal combustion engine measurements illustrate the mixture formation process for a pilot injection. Even at low injection mass of 3 mg, a strong penetration of the pilot is observed; fuel hits the piston bowl wall and is redirected upward to the cylinder head. Small amounts of fuel are also found to have penetrated into the bottom of the piston bowl. At top dead center, the pilot injection is still not completely homogeneously distributed in the piston bowl, and local equivalence ratios of Φ > 1 are found in the bowl.

Luminescence Properties of the Thermographic Phosphors Dy3+:YAG and Tm3+:YAG for the Application in High Temperature Systems

Abstract The high temperature sensitivity of the luminescence emission of thermographic phosphor (TP) particles favours its utilization for the measurement of wall or gas temperatures in combustion devices. The present work focuses on the luminescence behavior and suitability of two lanthanide ion types (Tm and Dy) doped in a YAG host crystal for high temperature applications. The Dy:YAG is a well-known thermographic phosphor and is used here as a reference for the comparison with Tm:YAG TP. Additionally its dopant concentration is varied to improve its signal intensity for high temperature applications. For the studied thermographic phosphors phosphorescence spectra, intensity ratios and luminescence decay time are characterized for a wide temperature range up to 1573 K.