Multispecies Raman imaging in flames by use of an unintensified charge-coupled device

Abstract

The application of an unintensified charge-coupled device (CCD) to one-dimensional multispecies Raman flame imaging is demonstrated. Relative signal strength is improved by the higher quantum efficiency of the unintensified CCD versus an intensified CCD generally used for Raman imaging. Experimental comparisons of unintensified and intensified CCD systems show ~40% improvement in the signal-to-noise ratios of major-species Raman signals for laboratory-scale H(2)-air flames. The maximum possible signal improvement is limited by the 40% transmission efficiency of the ferroelectric liquid-crystal light valve used to gate the CCD, although the light valve is demonstrated to be unnecessary for low-luminosity flames.

Assessment of a fast electro-optical shutter for 1D spontaneous Raman scattering in flames

“…Commercial mechanical shutters offer minimum opening times of several milliseconds, which is too long to efficiently remove flame emission and avoid the camera saturation. Wehrmeyer et al [17] were the first to propose the use of an unintensified CCD camera for SRS imaging in flames by using a ferroelectric liquid-crystal (FLC) shutter. The transmission of about 40% and a gate width of 40 µs did not allow the use of FLC as an optimal shutter for SRS detection in turbulent flames.…”

A mixing model providing joint statistics of scalar and scalar dissipation rate

“…The scalar dissipation rate is calculated with the model v ðiÞ ¼ p À2 C 0 / x ðiÞ ðz ðiÞ þ À z ðiÞ À Þ 2 : Based on z ðiÞ and v ðiÞ , the chemical composition vector / ðiÞ ¼ /ðz ðiÞ ; v ðiÞ Þ and the thermal state T ðiÞ ¼ T ðz ðiÞ ; v ðiÞ Þ are determined for every particle by employing tabulated steady laminar flamelet solutions. These flamelets were generated by simulating the opposed jet flame configuration of Wehrmeyer et al [19] with the help of the detailed reaction mechanism of Maas and Warnatz [6]. This reaction mechanism involves nine species and 37 steps and was used as a basis for the reduced mechanism employed by Ren and Pope [16].…”

A fast mechanical shutter for spectroscopic applications

“…On-off times of 1-2 ms are reported for this design, which represent only an order-of-magnitude improvement over large-format standard shutters. Electrooptical shutters based on ferroelectric liquid-crystal (FLC) polarization rotators have also been applied [8,9] to gate non-intensified cameras. On-off times between 40 and 80 µs are reported, with transmission efficiencies of up to 40% and extinction ratios as large as 5500:1.…”

“…Use of such a rotating mechanical shutter has been reported for application in LIDAR systems [11], although no details concerning speed and effective exposure time are presented. Similarly, relatively slow-speed, chopper-based shutters have been employed on spectrophosphorimeters [12] and coupled with FLC-based shutters to ameliorate the closed-state leakage [9] of these devices. Although the potential of a high-speed chopper-type shutter has been pointed out previously [9], no mention of the implementation of such a device is found in the literature.…”