Evaluation of the gaussian beam model for prediction of LDV fringe fields

A simple model is developed to estimate the fringe field geometry at the intersection of two Gaussian laser beams. Comparison of the model results to experimentally measured fringe spacing demonstrates that while the model predicts the fringe geometry well when the beam waists are far from the intersection volume, it performs poorly under nominally ideal conditions- when the beam waists are located at the intersection. Data obtained with two different laser sources indicate that the discrepancies between the theory and experiment are likely due to deviations of the laser beam from an ideal Gaussian beam. With a high quality laser, the details of the fringe field geometry are still not well duplicated by the Gaussian beam model, although the magnitude of the variation in fringe spacing and the effect of the controlling system parameters are correctly predicted

Optical diagnostics of diesel spray injections and combustion in a high-pressure high-temperature cell

Contains fulltext : 32816.pdf (publisher's version ) (Closed access)We report on spatially and temporally resolved optical diagnostic measurements of propagation and combustion of diesel sprays introduced through a single-hole fuel injector into a constant volume, high-temperature, high-pressure cell. From shadowgraphy images in non-reacting environments of pure nitrogen, penetration lengths and dispersion angles were determined for non-vaporizing and vaporizing conditions, and found to be in reasonable agreement with standard models for liquid jet propagation and break-up. Quasi-simultaneous two-dimensional images were obtained of laser elastic light scattering, shadowgraphs and spectrally integrated flame emission in a reacting environment (cell temperature 850 K). In addition laser-induced incandescence was employed for the identification of soot-loaded regions. The simultaneously recorded spray images exhibit remarkable structural similarity and provide complementary information about the spray propagation and combustion process. The measurements also reveal the fuel vapor cloud extending well beyond the liquid core and close to the nozzle tip. Ignition takes place close to the tip of the spray within the mixing layer of fuel vapor and surrounding air. Soot is formed in the vapor core region at the tip of the liquid fuel jet. Our results support recently developed phenomenological model on diesel spray combustion