Fuel Additive Transport into Engine Oil Determination using Laser Induced Fluorescence (LIF) and Liquid Chromatography (LC)

The transport of fuel-borne additives into the engine oil is a critical factor for the efficacy with which the additive functionality can be imparted on the engine. This paper describes the combination of Laser Induced Fluorescence (LIF) and Liquid Chromatography (LC) to determine the real-time additive concentrations and transfer ratios in a spark-ignition, 2-liter GM LHU engine. The current research used a continuous sample circuit from the engine sump which passed through an integrating cavity flow cell to enhance the LIF signal. In the absence of a fluorescence signature of any of the native additive species, a suitable fluorescing dye was selected to simulate the additive. After establishing rigorous calibration curves, LC was employed as a referee method to do a direct comparison with the LIF determined dye concentrations. The impact of the oil age and fuel dilution on the dye LIF signal was aggregated to a scaling factor which was a function of the relative absorption (RA) of the samples. In addition to the continuous LIF measurement, regular samples were used for RA determination and LC analyses. Based on the dye concentrations, transport ratios were determined which revealed the percentage of dye that accumulated in the engine oil over time. Good agreement was found between the transport ratios for the dye by the two methods.