Laser-induced fluorescence (LIF) measurements of NO concentration ([NO])have been obtained along the centerline of methane-air counterflow diffusion flames at 6 to 15 atm. This study is an extension of our previous work involving measurements of [NO] in similar flames at two to five atm, wherein we had used a counterflow premixed flame for calibration. For the flames studied here, a method based on computed overlap fractions is developed to calibrate [NO] measurements at higher pressures. The linear LIF measurements of [NO], which are corrected for variations in the electronic quenching rate coefficient, are compared with numerical predictions from an opposed-flow flame code utilizing two Gas Research Institute (GRI) chemical kinetic mechanisms (versions 2.11 and 3.0). The effect of radiative heat loss on code predictions is accounted for by using an optically thin radiation model. The revised GRI mechanism (version 3.0) offers a significant improvement in prompt-NO predictions for these flames compared to the older version (2.11), especially at pressures below eight atm. However, a consistent discrepancy remains in the comparisons, particularly at peak NO locations for pressures lower than six atm. The measurements display a continuing trend of decreasing NO concentration with increasing pressure at 6-15 atm as expected for flames dominated by prompt NO. The discrepancy between measurements and predictions decreases with rising pressure so that the revised GRI mechanism predicts [NO] with reasonable accuracy at pressures above six atm.
We report quantitative, spatially resolved laser-saturated fluorescence (LSF), linear laser-induced fluorescence (LIF), and planar laser-induced fluorescence (PLIF) measurements of nitric oxide (NO) concentration in a preheated, lean direct-injection spray flame at atmospheric pressure. The spray is produced by a hollow-cone, pressure-atomized nozzle supplied with liquid heptane, and the overall equivalence ratio is unity. NO is excited by means of the Q(2)(26.5) transition of the gamma(0, 0) band. LSF and LIF detection are performed in a 2-nm region centered on the gamma(0, 1) band. PLIF detection is performed in a broad ~70-nm region with a peak transmission at 270 nm. Quantitative radial NO profiles obtained by LSF are presented and analyzed so as to correct similar LIF and PLIF profiles. Excellent agreement is achieved among the three fluorescence methodologies.
The combustion diagnostics community has recently begun to focus
its efforts toward practical combustion devices. One impetus
behind this effort is the need to develop aeropropulsion gas
turbine combustors with ultra-low NOx emissions. For the
past several years, the Flame Diagnostics Laboratory at Purdue
University has been advancing optically non-intrusive techniques
to measure concentrations of nitric oxide [NO] in lean
direct-injection (LDI) spray flames. LDI flames offer the
possibility of reducing NOx emissions from gas turbines by
rapid mixing of the liquid fuel and air so as to drive the flame
structure toward partially premixed conditions. In this paper,
we review the technical approach required to utilize
laser-induced fluorescence (LIF) methods for quantitatively
measuring [NO] in LDI spray flames. In the progression from
atmospheric to high-pressure measurements, the LIF method
requires a shift from the saturated to the linear regime of
fluorescence measurements. As such, we discuss quantitative,
spatially resolved laser-saturated fluorescence (LSF), linear
laser-induced fluorescence (LIF) and planar laser-induced
fluorescence (PLIF)
measurements of NO concentration in atmospheric, LDI spray
flames. In general, the results are comparable, although novel
filtering techniques are required at higher flame pressures.
Instantaneous audiovisual feedback training on CC quality produces immediate improvements in compression rate, hand placement, as well as depth and recoil compliance. These improvements, however, are not retained 1 year later. Improved depth performance may be correlated to an increased training frequency.
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