Laser-Induced Emission Techniques for Concentration and Temperature Probing in Combustion

Sammanfattning: The work in this thesis is aimed at the development of temperature and gas concentration measurement techniques in laser diagnostics for use in combustion research. The techniques are developed as tools for the combustion community to meet future demands on combustion efficiency and legislation of exhaust gases. Thermometry based on the use of laser-induced phosphorescence has been further developed and performed inside internal combustion engines, in a gas turbine afterburner, in burning liquids, and in research on oxy-fuel flame heat transfer. In work carried out within the EU 6:th framework program, an attempt was made to find new suitable thermographic phosphors for high temperature two-dimensional measurements in gas turbines. The gas turbine industry has a strong interest in better methods of thermometry at high temperatures for optimizing performance of combustion and engine parts. Measurements on spinning objects require the use of fast phosphors, previously unavailable for high-temperature two-dimensional measurements. A variety of inorganic phosphor materials, not previously used in thermometry, were investigated, some of them being very promising for thermographic use. Laser-induced oxygen sensing using a commercial pressure sensitive paint has been applied in low-temperature combustion. The material has been calibrated to oxygen and temperature. The work show on the potential of using oxygen quenched materials in combustion research even though it involves organic sensing materials. Laser-Induced Fluorescence was employed for visualization of formaldehyde both in Homogeneous Charge Compression Ignition, HCCI, and in Diesel combustion engines. Formaldehyde formed in HCCI combustion during low temperature reactions was shown to be able to function as fuel marker. This was demonstrated in simultaneous visualization of the traditional fuel tracer toluene and formaldehyde during operation of an HCCI engine. The use of formaldehyde as a fuel marker was also demonstrated in Diesel combustion, which is characterized by a lack of low temperature reactions and where the location of intermediate species is not obvious. Fuel visualization was also employed for the visualization of jet fuel in a jet stream of a fighter-jet gas turbine. Un-burnt fuel was found to exist in the exhaust for some engine conditions.