Optimizing Precision and Accuracy of Quantitative PLIF of Acetone as a Tracer for Hydrogen Fuel 2009-01-1534

Quantitative planar laser-induced fluorescence (PLIF) of gaseous acetone as a fuel-tracer has been used in an optically accessible engine, fueled by direct hydrogen injection. The purpose of this article is to assess the accuracy and precision of the measurement and the associated data reduction procedures. A detailed description of the acetone seeding system is given as well. The key features of the experiment are a high-pressure bubbler saturating the hydrogen fuel with acetone vapor, direct injection into an optical engine, excitation of acetone fluorescence with an Nd:YAG laser at 266 nm, and detection of the resulting fluorescence by an unintensified camera. Key steps in the quantification of the single-shot imaging data are an in-situ calibration and a correction for the effect of local temperature on the fluorescence measurement. We assess the accuracy of the measurement in terms of drift in acetone-vapor concentration, linearity of fluorescence with laser energy, absorption of the beam within the probe volume, spatial inhomogeneity in the calibration measurements, and uncertainties in the temperature correction. The precision is impacted by camera read-out noise, shot (quantum) noise, shot-to-shot variations in total laser-pulse energy and the transverse energy profile, and “beam steering” by thermal gradients. Procedures to quantify and if possible minimize all of the above factors are described. Among the factors investigated, the single greatest impact on accuracy and precision has uncertainty in the calibration of global equivalence ratio and refractive beam steering, respectively.