High-speed low-coherence interferometry of fuel films in impinging gasoline direct injection sprays

Abstract

Quantitative experimental characterization of dynamic fuel film deposition processes is critical to developing better understanding and modeling of cold-start behavior in gasoline direct injection engines. Low-Coherence Interferometry (LCI) offers a quantitative fuel film thickness diagnostic that is immune or resistant to major confounding influences that limit other optical diagnostics in engine-relevant environments. This work describes an extension of spectral LCI techniques to high-speeds (10 kHz) that are capable of resolving the dynamics of fuel film deposition and evaporation in impinging gasoline sprays. Two approaches to LCI, Michelson interferometry and Fizeau interferometry, were tested and results demonstrate the superiority of the Fizeau configuration for enclosed vessel experiments. Experiments were performed at cold start conditions in an enclosed spray chamber with a gasoline spray impinging on a transparent wall. High-speed LCI was used to measure fuel film thicknesses and dynamic changes in thickness. The measurements were used to observe variation in film thickness and behavior with changes in system temperature and fuel composition.