Development of High-Speed Laser Diagnostics for the Investigation of Scalar Heterogeneities.

Abstract

The development of advanced engine concepts are, to a large extent, hindered by the lack of suitable multidimensional optical diagnostics that can measure heterogeneities in engines. The combustion process is a complex function of species concentration, temperature, pressure, and flow fields. Fine-tuning the combustion process for efficient combustion with low emissions therefore requires detailed knowledge of these parameters as they vary with space and time. Novel optical diagnostic techniques which probe relevant quantities can either be used to address a specific problem, as with misfires and partial burns in a spark ignition direct-injection (SIDI) stratified charge (SC) gasoline engines; to develop models, such as boundary layer temperature field measurements; or serve both purposes. For these two examples, there are currently no diagnostics which meet the needs of engine developers and modelers, which motivated the current work. Investigations of misfires and partial burns can benefit from novel and improved fuel concentration and combustion progress diagnostics. A high-speed, planar, quantitative fuel concentration diagnostic technique based on laser-induced fluorescence (LIF) of biacetyl was utilized in unison with a spark plug absorption probe to aid in the understanding of both approaches. The LIF diagnostic was improved by using a dual laser approach which increased the signal to noise ratio. Also, its ability to track flame fronts and observe outgassing from engine crevices was demonstrated. The suitability of xxii the spark plug absorption probe for use in an SIDI SG engine was demonstrated. Next, a simplified combustion progress diagnostic using LIF of hydroxyl radicals was demonstrated, which avoids the cost and complexity associated with conventional approaches. Lastly, a novel, high speed, high resolution LIF diagnostic called two color toluene thermometry was developed to quantitatively measure boundary layer temperature fields. Calibration measurements were performed in a heated jet. The diagnostics were then adapted from a two camera design to a single camera design for simplicity and used to evaluate temperature gradients in an engine boundary layer. The results provided insight into the structure of the boundary layer during different parts of the engine cycle and for different engine operation conditions.