Combustion analysis

Abstract

Excimer lasers are excellent tools not only for micro-machining and material processing, but also for measurement applications. The unique combination of high-brightness laser emission in the UV spectral range and wavelength tuning makes these laser systems extremely suitable for monitoring of different molecules, like H2, O2, CO2, CO, NO, OH, CH, and a variety of hydrocarbons. These molecules are major or minor components of the atmosphere as well as important constituents of high pressure/high temperature technical combustion systems and facilities. The spatial and temporal distribution of these species can be detected, even in complex chemical and physical environments, owing to the short pulse duration and high pulse energy of excimer laser light. Excimer lasers are therefore well suited for spectroscopic analysis of technically applied combustion processes and their optimization in car engines and powerplants. The main objectives in this context are the improvement of fuel consumption and the reduction of pollutant emissions from these technical systems. A detailed understanding of the complex non-stationary and multiply interwoven processes inside the combustion chambers like fuel atomization, vaporization, mixture formation, combustion and pollutant formation is required. Chemical reaction kinetics and the gas dynamical phenomena demand the knowledge of physical properties, like density-and temperature gradients, size, distribution and temperature of fuel droplets, distribution of liquid and already vaporized fuel, etc. The information can be obtained by using excimer lasers in connection with different diagnostic techniques, including Mie-, Rayleigh-and Ramanscattering, laser-induced fluorescence and its various derivatives [1, 2, 3, 4]. By combining these techniques with efficient detection equipment like intensified CCD cameras or spatially resolving optical multichannel analyzers, sensitive and powerful measurement systems can be built, which are comparatively simple because most of the above mentioned techniques use the same basic experimental set-up with only minor changes. In the following, some techniques are briefly described. © 2005 Springer-Verlag Berlin Heidelberg.