Experimental determination of pdfs of OH radicals in IC engines using calibrated laser-induced fluorescence as a basis for modelling the end-phase ofengine combustion

An experimental approach based on the simultaneous measurement of laser-ind uced fluorescence along a line and the transmission is discussed which allo ws the quantitative measurement of combustion intermediates. The technique is applied to measure in-cylinder number densities of OH radicals using an optically accessible two-stroke engine. OH radicals are recorded for differ ent cylinder pressures during the expansion stroke. From the data pressure dependent probability density functions (pdfs) are obtained. precalculated combustion scenarios based on an opposed jet geometry and on a homogeneous reaction scheme are used to analyse correlations between the measured OH nu mber densities and other scalars. e.g., the temperature and O-atoms which a re important For the determination of NO, emissions in post-processing step s of CFD calculations. By the use of experimentally obtained pdfs for the O H radical and the correlation analyses, an improved estimation of pdfs for the temperature and O-atoms is presented.