Simultaneous high-speed gas property measurements at the exhaust gas recirculation cooler exit and at the turbocharger inlet of a multicylinder diesel engine using diode-laser-absorption spectroscopy.

A diode-laser-absorption-spectroscopy-based sensor system was used to perform high-speed (100 Hz to 5 kHz) measurements of gas properties (temperature, pressure, and H(2)O vapor concentration) at the turbocharger inlet and at the exhaust gas recirculation (EGR) cooler exit of a diesel engine. An earlier version of this system was previously used for high-speed measurements of gas temperature and H(2)O vapor concentration in the intake manifold of the diesel engine. A 1387.2 N m tunable distributed feedback diode laser was used to scan across multiple H(2)O absorption transitions, and the direct absorption signal was recorded using a high-speed data acquisition system. Compact optical connectors were designed to conduct simultaneous measurements in the intake manifold, the EGR cooler exit, and the turbocharger inlet of the engine. For measurements at the turbocharger inlet, these custom optical connectors survived gas temperatures as high as 800 K using a simple and passive arrangement in which the temperature-sensitive components were protected from high temperatures using ceramic insulators. This arrangement reduced system cost and complexity by eliminating the need for any active water or oil cooling. Diode-laser measurements performed during steady-state engine operation were within 5% of the thermocouple and pressure sensor measurements, and within 10% of the H(2)O concentration values derived from the CO(2) gas analyzer measurements. Measurements were also performed in the engine during transient events. In one such transient event, where a step change in fueling was introduced, the diode-laser sensor was able to capture the 30 ms change in the gas properties; the thermocouple, on the other hand, required 7.4 s to accurately reflect the change in gas conditions, while the gas analyzer required nearly 600 ms. To the best of our knowledge, this is the first implementation of such a simple and passive arrangement of high-temperature optical connectors as well as the first documented application of diode-laser absorption for high-speed gas dynamics measurements in the turbocharger inlet and EGR cooler exit of a diesel engine.

Perturbative theory and modeling of electronic-resonance-enhanced coherent anti-Stokes Raman scattering spectroscopy of nitric oxide.

A theory is developed for three-laser electronic-resonance-enhanced (ERE) coherent anti-Stokes Raman scattering (CARS) spectroscopy of nitric oxide (NO). A vibrational Q-branch Raman polarization is excited in the NO molecule by the frequency difference between visible Raman pump and Stokes beams. An ultraviolet probe beam is scattered from the induced Raman polarization to produce an ultraviolet ERE-CARS signal. The frequency of the ultraviolet probe beam is selected to be in electronic resonance with rotational transitions in the A (2)Sigma(+)<--X (2)Pi (1,0) band of NO. This choice results in a resonance between the frequency of the ERE-CARS signal and transitions in the (0,0) band. The theoretical model for ERE-CARS NO spectra has been developed in the perturbative limit. Comparisons to experimental spectra are presented where either the probe laser was scanned with fixed Stokes frequency or the Stokes laser was scanned with fixed probe frequency. At atmospheric pressure and an NO concentration of 100 ppm, good agreement is found between theoretical and experimental spectral peak locations and relative intensities for both types of spectra. Factors relating to saturation in the experiments are discussed, including implications for the theoretical predictions.

Measurement of nitric oxide concentrations in flames by using electronic-resonance-enhanced coherent anti-Stokes Raman scattering.

We have measured nitric oxide (NO) concentrations in flames by using electronic-resonance-enhanced coherent anti-Stokes Raman spectroscopy (ERE-CARS). Visible pump and Stokes beams were tuned to a Q-branch vibrational Raman resonance of NO. A UV probe beam was tuned into resonance with specific rotational transitions in the (v"=1,v'=0) vibrational band in the A(2)Sigma(+)-X(2)Pi electronic transition, thus providing a substantial electronic-resonance enhancement of the resulting CARS signal. NO concentrations were measured at levels down to 50 parts in 10(6) in H(2)/air flames at atmospheric pressure. NO was also detected in heavily sooting C(2)H(2)/air flames at atmospheric pressure with minimal background interference.

Measurements of absolute CH concentrations by cavity ring-down spectroscopy and linear laser-induced fluorescence in laminar, counterflow partially premixed and nonpremixed flames at atmospheric pressure.

We report quantitative, spatially resolved measurements of methylidyne concentration ([CH]) in laminar, counterflow partially premixed and nonpremixed flames at atmospheric pressure by using both cavity ring-down spectroscopy (CRDS) and linear laser-induced fluorescence (LIF) in the A-X (0, 0) band. Three partially premixed (phiB = 1.45, 1.6, 2.0) flames plus a single nonpremixed methane-air flame are investigated at a global strain rate of 20 s(-1). These quantitative measurements are compared with predictions from an opposed-flow flame code when utilizing two GRI chemical kinetic mechanisms (versions 2.11 and 3.0). The LIF measurements of [CH] are corrected for variations in the electronic quenching rate coefficient by using predicted major species concentrations and temperatures along with quenching cross sections for CH that are available in the literature. The peak CH concentration obtained by CRDS is used to calibrate the quenching-corrected LIF measurements. Excellent agreement is obtained between CH concentration profiles measured by using the CRDS and LIF techniques. The spatial location of the CH layer is very well predicted by GRI 3.0; moreover, the measured and predicted CH concentrations are in good agreement for all the flames of this study.