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Improved understanding of the active combustion chain “injection - vaporisation - mixture formation - ignition - combustion - exhaust gas emissions” is important for the further development of IC engines with respect to fuel consumption and pollutant emissions. By means of multidimensional optical, mostly laser-based measurement techniques, a modern passenger car common rail system, applied to an optically accessible engine, was investigated. The utilisation of a new optical detection system allowed a simultaneous detection of the liquid phase by Mie scattering, the flame propagation from flame luminosity and the soot formation by laser-induced incandescence inside the combustion bowl of the engine. By such simultaneous measurements, direct dependencies of single combustion phenomena on fuel injection parameters can be resolved, and in particular soot formation and oxidation can be correlated to the actual combustion situation.

In previous work, time-resolved laser-induced incandescence (TIRE-LII) has been introduced as a favorable and easy-to-use technique for accurate online measurements of soot within the exhaust gas of production engines without modifications and first experimental results have been presented. The method relies on the detection of the thermal radiation of the particles after heating with a high power laser pulse. Additionally to soot concentration measurements, a simultaneous determination of soot primary particle sizes and, derived from these, also of the particle number concentrations is possible. Basic features of the technique are the high temporal resolution, which also makes transient tests feasible, and its high sensitivity and selectivity. These aspects suggest its application as a standard method for exhaust measurements with enhanced performance, which also leads to considerable new insight into internal combustion phenomena.