Mixture of triethylamine (TEA) and benzene as a new seeding material for the quantitative two-dimensional laser-induced exciplex fluorescence imaging of vapor and liquid fuel inside SI engines

Abstract A mixture of triethylamine (TEA) and benzene in iso-octane has been proven to be a suitable seeding material for the study of the gasoline fuel mixture and evaporation processes under engine-like conditions. Laser-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 properties that match well with the model fuel iso-octaine 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 evaporation and mixture formation processes in SI engines. In the liquid phase, the mixture of the two tracer substances with iso-octane shows a broadband fluorescence spectrum which is red-shifted with respect to the vapor-phase fluorescence. This allows a spectrally separated detection of the local distributions of the liquid and the vapor phases by using appropriate bandpass filters. Vapor-phase fluorescence in the presence of synthetic air, oxygen, nitrogen, carbon dioxide, and water vapor under variation of pressure, concentration, and temperature was measured in a heatable high-pressure chamber. It has been found that oxygen is the only molecular species which induces collisional quenching of 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 that the fluorescence intensity is directly proportional to the fuel/air-ratio and independent of pressure for pressures higher than 3 bar. The temperature dependence of the fluorescence intensity has been studied in a temperature range from 398 to 523 K. With increasing temperature, a systematic decrease of the fluorescence intensity has been detected, which, however, is still directly proportional to the fuel/air ratio. An application of the newly developed tracer combination for the quantitative two-dimensional imaging of the fuel/air-ratios in the vapor-phase and the simultaneous, spectrally separated detection of the liquid phase inside an SI engine is presented.

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