Search

Abstract Simultaneously calibrated, non-linear two-line atomic fluorescence (SC-nTLAF) thermometry for application in turbulent sooting flames has been developed to increase the precision of single-shot, planar measurements of gas temperature. The technique has been demonstrated in both steady and turbulent sooting flames, showing good agreements with previous optical measurements. The SC-nTLAF involves imaging simultaneously laser-induced fluorescence (LIF) of atomic indium in both the target flame and a non-sooting calibration flame for which the temperature distribution is known. The LIF intensities from the reference flame enable correction for fluctuations, not only in the laser power, but also in the laser mode. The resulting precision was found to be ±67 K and ±75 K (based on one standard deviation) in the rich and oxidizing regions of a steady sooting flame for which the measured temperature was 1610 K and 1854 K, respectively, with a spatial resolution of 550 × 550 µm2. This corresponds to a relative precision of ∼ 4.1%. The resulting precision in the single-shot temperature images for a well-characterized, lifted ethylene jet diffusion flame (fuel jet Reynolds number = 10,000) compares favorably with previously reported data obtained with shifted-vibrational coherent anti-Stokes Raman spectroscopy (CARS), together with increased spatial resolution. The planar imaging also provides more details of the temperature distribution, particularly in the flame brush region, which offers potential for measurement of more parameters, such as gradients and spatial corrections. The new calibration method has also achieved a significant time-saving in both data collection and processing, which is an estimated total of ∼ 60%–70% compared with conventional nTLAF. [ABSTRACT FROM AUTHOR]

Abstract: High-speed laser induced fluorescence (LIF) thermometry is combined with particle image velocimetry (PIV) to measure the temporal evolution of the spatial unburned gas temperature distribution in a motored spark-ignition (SI) optical engine. Single-line excitation of toluene and subsequent two-color emission detection is employed for LIF thermometry. Precision uncertainty is assessed pixel-wise and found to be ±5K at 295K and ±29K at 550K, but decreases by 34% (i.e., ±19K at 550K) when spatially averaging the LIF signal over a 10×10pixel2 region. The polytropic temperature relation is used to correlate LIF ratio with temperature to calibrate the in-cylinder gas temperature measurements. Instantaneous temperature images and temperature PDFs show homogeneous temperature distribution during compression, while significant temperature inhomogeneities from entrained colder gases are captured during early expansion. Simultaneously acquired PIV and LIF images illustrate the evolution of the cold gas distribution during expansion. The images presented reveal the capability of high-speed toluene-LIF thermometry combined with PIV in an engine to capture the 2D temperature distribution and track structures of colder temperatures. [Copyright &y& Elsevier]

Abstract: Direct-injection (DI) concepts with spray-guided mixture formation are promising methods to increase the efficiency of spark ignition (SI) engines. The fuel and temperature distribution determines evaporation and ignition behavior. However, the resulting mixture and temperature are not homogeneous through the combustion chamber. Furthermore, it is strongly affected by the fuel evaporation properties, which are different for modern biofuels compared to gasoline. The present paper demonstrates the procedure and the capability of two-line excitation LIF based on 3-pentanone for accurate planar temperature determination in DISI-sprays at late injection timing conditions. The jet temperature profiles were determined for the gasoline surrogate fuel iso-octane and the biogenic component ethanol, which have a significant difference in their heat of evaporation. The spray of a 6-hole solenoid-injector in an optically accessible combustion test rig is analyzed by quasi-simultaneous excitation by two different excimer lasers. The signals are recorded with one double-shutter ICCD-camera. From the signal ratio of the images the temperature field in the fuel spray can be calculated. The tracer is calibrated with an enhanced high temperature calibration cell for temperatures up to 700K and pressures up to 1MPa, which are relevant for the studied conditions. The postprocessing strategy is optimized regarding high accuracy and precision. The fuel spray behavior is evaluated at different positions in the spray and times showing larger evaporation cooling in the jet of maximum 141K for ethanol. For a comparison of the ensemble averaged results a CFD-spray model was set up under the same boundary conditions showing very similar trends. The temperature images yielded a single-shot precision of approximately 5.6% and inaccuracies of 3.8% making this technique capable for model improvements and validation. [Copyright &y& Elsevier]