Use of LIF image acquisition and analysis in developing a calibrated technique for in-cylinder investigation of the spatial distribution of air-to-fuel mixing in direct injection gasoline engines

This paper presents the role of image acquisition and analysis in the development of a new strategy for the calibration of measurements of fuel distribution in gasoline direct injection engines. Images are acquired from a motored experimental engine that features a quartz ring in its upper cylinder construction. A carefully chosen fuel analogue is labelled with a fluorescent tracer. Illumination of the gas charge in the cylinder with a powerful UV laser results in laser-induced fluorescence (LIF) that is observed with an intensified camera. The objective is to obtain a two-dimensional map of tracer concentration in the cylinder, which allows the fuel distribution to be inferred, in order to be able to study the mixing process of air and fuel. A detailed understanding of this process is critical to the design of next generation (direct injection) gasoline engines, if they are to meet forthcoming emission regulations. The carefully considered scene illumination, image acquisition and image analysis techniques described in this paper play key roles in facilitating the advancement of the LIF technique to a point that permits examination of cycle-to-cycle variability of the injection process, for example. A new approach to coping with the fluorescence dependency on pressure and temperature, the issues related to the choice of a fluorescence tracer, the careful determination of the optimum tracer concentration, and the complete calibration methodology are described. The paper concludes with some examples of calibrated measurements, which validate the design assumptions. (c) 2005 Published by Elsevier B.V.