IN-SITU MEASUREMENT OF FUEL IN THE CYLINDER WALL OIL FILM OF A COMBUSTION ENGINE BY LIF SPECTROSCOPY

Hydrocarbon emissions remain an important concern for the automotive i ndustry due to increasingly strict regulations. In an investigation of possible emission sources within the engine, the concentration of fue l absorbed in the oil film on the cylinder wall of a small internal co mbustion engine has been measured with laser-induced fluorescence (LIF ) spectroscopy, A laser pulse from a nitrogen laser (337.1 nm) provide d the excitation, and the fluorescence was monitored with an intensifi ed-charge-coupled device (ICCD) array mounted to a spectrometer. The e xcitation laser pulse was launched through a window in the engine head onto a fiber-optic probe mounted flush with the cylinder wall. The la ser-excited oil film on the fiber-optic probe produced an LIF signal t hat was collected by the fiber-optic probe and analyzed for fuel conte nt. The timing of the laser pulse and ICCD gate were controlled in ord er to synchronize the collection of data with a particular point in th e engine cycle. Measurements made in situ, while the engine was runnin g, yield information on the amount of unburned fuel stored in the oil film for various engine conditions. Fuel-in-oil concentrations were de termined for various engine temperatures during cold starts, for diffe rent fuel enrichment levels, and as a function of the crank angle of t he engine cycle. Fuel concentrations as high as 50% were detected duri ng cold starts, and fuel concentrations reached levels greater than 25 % for warm engine operation. Changes in the fuel content were also fou nd to be related to enrichment and crank angle.