MIXTURE OF TRIETHYLAMINE (TEA) AND BENZENE AS A NEW SEEDING MATERIAL FOR THE QUANTITATIVE 2-DIMENSIONAL LASER-INDUCED EXCIPLEX FLUORESCENCEIMAGING OF VAPOR AND LIQUID FUEL INSIDE SI ENGINES

A mixture of triethylamine (TEA) and benzene in iso-octane has been pr oven to be a suitable seeding material for the study of the gasoline f uel mixture and evaporation processes under engine-like conditions. La ser-induced fluorescence (LIF) of the exciplex-forming mixtures of TEA and benzene has been investigated using a KrF-excimer laser at 248 nm as an excitation source. The dopants have physical and chemical prope rties that match well with the model fuel iso-octane and show only low absorption at the excitation wavelength. These are important criteria for materials to be used as tracer substances for the study of evapor ation and mixture formation processes in SI engines. In the liquid pha se, the mixture of the two tracer substances with iso-octane shows a b roadband fluorescence spectrum which is red-shifted with respect to th e vapor-phase fluorescence. This allows a spectrally separated detecti on of the local distributions of the liquid and the vapor phases by us ing appropriate bandpass filters. Vapor-phase fluorescence in the pres ence of synthetic air, oxygen, nitrogen, carbon dioxide, and water vap or under variation of pressure, concentration, and temperature was mea sured in a heatable high-pressure chamber. It has been found that oxyg en is the only molecular species which induces collisional quenching o f the fluorescence emissions. Hence, using the described tracer system , a quantitative detection of vapor-phase concentrations and fuel/air- ratios under engine like conditions is possible. It is demonstrated th at the fluorescence intensity is directly proportional to the fuel/air -ratio and independent of pressure for pressures higher than 3 bar. Th e temperature dependence of the fluorescence intensity has been studie d in a temperature range from 398 to 523 K With increasing temperature , a systematic decrease of the fluorescence intensity has been detecte d, which, however, is still directly proportional to the fuel/air rati o. An application of the newly developed tracer combination for the qu antitative two-dimensional imaging of the fuel/air-ratios in the vapor -phase and the simultaneous, spectrally separated detection of the liq uid phase inside an SI engine is presented. (C) 1998 by The Combustion Institute.