Molecular beam overrun in sampling transient combustion processes

Effects of combustion generated source temperature variations on direct sampling in a molecular beam mass spectrometer is examined.The problem of particular concern is the influence of beam overrun on the distribution of .~ molecules arriving at the detector.The overrun is due to the fact that the hotter, and thus faster, constituents of the molecular beam are formed later than its colder, and thus slower, portions.Photolysis of N0 2 in Ar and flash ignited mixtures of Ar/CH 4 /0 2 /N0 2 using a chopped molecular beam time-of-flight technique yields time resolved temperature measurements, while concomitant numerical analysis accurately predicts the observed beam overrun.Analysis of continuous sampling in representative transient combustion processes indicates that the molecular beam mass spectrometer is capable of measuring meaningful time-resolved concentration profiles.2 •