Gustaf Särner

Investigations of blue emitting phosphors for thermometry

Blue emitting phosphors are investigated and reported for possible use in thermometry. Currently reported thermographic phosphors in general have the drawback of long emission lifetimes obstructing the possibility to time gate for background discrimination. An additional problem is that many thermographic phosphors have emission in the red spectral region, making them vulnerable for black body radiation at high temperatures. This work reports the temperature sensitivity for nine phosphors considered suitable for accurate temperature measurements in harsh conditions both in single points and in two dimensions (2D).

Survivability of thermographic phosphors (YAG:Dy) in a combustion environment

The feasibility of applying laser-induced phosphorescence in a combustion environment was shown by testing the consistency of the emission‐temperature relations of thermographic phosphor particles (YAG:Dy). The relations were calibrated before and after the phosphor particles had passed a flame front. The calibrations were performed in air and in pure oxygen. The emission‐temperature relation prevails from around 300 K to 1300 K. The difference in emission‐temperature relation for the two different cases is less than the experimental precision (3%).

Two-dimensional thermometry using temperature-induced line shifts of ZnO:Zn and ZnO:Ga fluorescence.

Sensitive temperature-induced line shifts of the near-band-edge emission from ZnO:Ga and ZnO:Zn are investigated for two-dimensional (2D) thermometry with nanosecond time resolution. Spectral and temporal concerns for 2D measurements and the feasibility for utilizing the line shifts for temperature measurements using a spectral ratio are investigated. Owing to the high temperature sensitivity, a precision of 1% at 800 K is reported for spectral ratio measurements. The technique is demonstrated by 2D measurements of the liquid temperature of burning methanol droplets.

Cycle Resolved Wall Temperature Measurements Using Laser-Induced Phosphorescence in an HCCI Engine

Cycle-resolved wall temperature measurements have been performed in a one-cylinder, port-injected optical Scania D12 truck engine run in HCCI mode. Point measurements at various locations were made using Laser-Induced Phosphorescence (LIP). Single point measurements with thermographic phosphors utilize the temperature dependency of the phosphorescence decay time. The phosphorescence peak at 538 nm from the thermographic phosphor La2O2S:Eu was used to determine temperature. A frequency tripled 10 Hz pulsed Nd:YAG laser delivering ultraviolet (UV) radiation at 355 nm was used for excitation of the phosphor. Detection in the spectral region 535 - 545 nm was performed every cycle with a photo multiplier tube connected to a 3 GHz oscilloscope. Measurements were made at four points on the cylinder head surface and two points on the outlet and inlet valves respectively. For each location measurements were made at different loads and at different crank angle degrees (CAD). The aim of the presented work was to study the feasibility of using LIP for single-shot, cycle-resolved wall temperature measurements. (Less)

Simultaneous PLIF Measurements for Visualization of Formaldehyde- and Fuel- Distributions in a DI HCCI Engine

Simultaneous laser-induced fluorescence (LIF) imaging of formaldehyde and a fuel-tracer have been performed in a direct-injection HCCI engine. A mix of N-heptane and iso-octane was used as fuel and Toluene as fluorescent tracer. The experimental setup involves two pulsed Nd:YAG lasers and two ICCD cameras. Frequency-quadrupled laser radiation at 266 nm from one of the Nd:YAG lasers was used for excitation of the fuel tracer. The resulting fluorescence was detected with one of the ICCD cameras in the spectral region 270-320 nm. The second laser system provided frequency-tripled radiation at 355 nm for excitation of formaldehyde. Detection in the range 395-500 nm was achieved with the second ICCD. The aim of the presented work is to investigate the applicability of utilizing formaldehyde as a naturally occurring fuel marker. Formaldehyde is formed in the low-temperature reactions (LTR) prior to the main combustion and should thus be present were fuel is located until it is consumed. Measurements were performed when injecting fuel early and late in the compression stroke. Early injection timing results in a homogeneous charge at the time of auto-ignition, while late timing gives a more stratified charge. The crank angle position at which measurements were performed was altered to cover the entire combustion cycle. The measurement images show instantaneous distributions of toluene and formaldehyde respectively. Images from both early and late injection and at all crank angle degrees show good spatial resemblance between toluene signal area and formaldehyde signal area. The work presented in this paper shows that formaldehyde is a feasible alternative to traditional fuel tracers for visualizing fuels featuring low-temperature reactions in HCCI combustion

Optical diagnostics for characterization of a full-size fighter-jet afterburner

In the present work the feasibility of using various optical/laser based techniques for characterization of the afterburner of a full-size aircraft engine have been investigated. The tests have been performed on-site at Volvo Aero Corporation and were mainly directed towards surface thermometry using thermographic phosphors and fuel visualization. All applications were studied for different engine running conditions, including various use of the afterburner (A/B). Laser-Induced Fluorescence (LIF) was employed for fuel visualization to investigate to what extent unburned fuel exits the afterburner. Laser-Induced Phosphorescence (LIP) from thermographic phosphors was used to measure two-dimensional surface temperatures on the outlet nozzle of the afterburner. In addition, the spectral characteristics of the burning jet stream were investigated. Copyright

Simultaneous Formaldehyde and Fuel-Tracer LIF Imaging in a High-Speed Diesel Engine With Optically Accessible Realistic Combustion Chamber

Simultaneous laser-induced fluorescence (LIF) imaging of formaldehyde and a fuel-tracer have been performed in a high-speed diesel engine. N-heptane and isooctane were used as fuel and toluene was used as a tracer. This arrangement made it possible to make simultaneous measurements of toluene by exciting at 266 nm and detecting at 270-320 nm while exciting formaldehyde at 355 nm and detecting at 400-500 nm.The aim of this study is to investigate how traditional fuel tracer and natural-occurring formaldehyde formed in the cool chemistry are transported in the piston bowl. A range of ignition delays were created by running the engine with different amounts of EGR. During this sweep the area where the low-temperature reactions take place were studied.The measurements were performed in a 0.5-l, single-cylinder optical engine running under conditions simulating a cruise-point, i.e., about 2.2 bar imep. The ignition delay was elongated compared to the normal mapping and the engine-out emissions of soot and NOx were ultra-low.It was found that the spatial location of LTRs does not shift significantly for different EGR levels. The formaldehyde signal overlaps the fuel signal in most cases before the onset of the main heat release.

Using oxygen-quenched pressure-sensitive paint for oxygen concentration measurements in low-temperature combustion environments

The feasibility of using pressure-sensitive paint for oxygen concentration measurements in low-temperature combustion environments has been investigated and applied to slow combustion processes. In addition, the temperature limitation for this application was studied. A Nd:YAG laser system, a PMT and fiber-optics were used for developing a compact probe for oxygen measurements. The lifetime sensitivity to oxygen concentration and temperature of a commercially available pressure-sensitive paint has been investigated with regard to possible abilities and limitations. After calibrations with regard to temperature, measurements in slow combustion environments showed that the technique is capable of accurately measuring oxygen concentration in environments up to 180 °C. The measurements indicate usability also in the combustion area despite issues of thermal quenching and quenching from NO. The compact design of the system makes it a useful tool for oxygen measurements in situations where suction probes and other oxygen measurement techniques are too intrusive.

Laser-induced phosphorescence spectroscopy: development and application of thermographic phosphors (TP) for thermometry in combustion environments

In this chapter a temperature probing technique based on the spectroscopy of inorganic luminescent materials is described and exemplified in experiments related to combustion. The basic features of thermographic phosphors which enable remote temperature diagnostics to be performed with a high degree of sensitivity and accuracy, are outlined. This technique is superior to those based on thermocouples and pyrometry, particularly in the vicinity of flames and when the measured surface is subjected to random movements. Many thermographic phosphors have the property of being insensitive to variations in pressure up to 1 GPa. This property extends the use and development of thermographic thermometry to such domains as internal combustion engines and gas turbines, for which examples are also provided.