Temperature Measurement in Plasma-Assisted Combustor by TDLAS

Abstract

The paper is focused on measurements of gas temperature distribution in plasma-assisted supersonic combustor. A tunable diode laser absorption spectroscopy (TDLAS) technique was applied for that. Spectra of H2O absorption were recorded using fast frequency scanning of a single distributed feedback (DFB) laser. Under conditions of high level of flow disturbances an optimal technique for fitting the experimental spectra was developed based on visualization of the transient absorption spectra as 2D images in the first step of data processing. In the most cases the high signal-to-noise ratio enabled the reconstruction of the temporal behavior of temperature with a resolution of ∼1ms. Direct wall-injected ethylene was used as the fuel in two geometrical configurations: fuel orifices upstream or downstream of the electrode system of near-surface electric discharge. Conformity of the data of DLAS measurement with the two-stage mechanism of plasma-assisted combustion is discussed. I. Introductionvariety of optical diagnostic techniques are used for gaseous medium characterization at presence of electrical discharge plasma-optical emission spectrometry (OES), Thomson scattering (TS), coherent anti-stocks Raman scattering (CARS), Doppler line broadening, etc. These techniques, providing valuable data for specific types of plasma and specific range of plasma parameters, have some limitations. Tunable diode laser (DL) absorption spectroscopy (TDLAS) is a widely used spectroscopic technique for the detection of gas parameters in reacting flows [1][2][3][4][5][6][7][8]. This technique provides remote, non-intrusive measurements of the parameters of a hot zone with time resolution in the µs-ms range depending on the specific experimental conditions. The technique is usually based on the measurements of the ratio of the absorption line intensities of a test molecule. If a Boltzmann distribution of the energy levels is established, the ratio of the line intensities depends only on the kinetic temperature of the object.DLAS possesses many attractive features as the diagnostic technique. The spatial coherence of DLs enables to deliver a narrow laser beam to a probing zone without noticeable divergence, which makes it possible remote sensing. In contrast to any version of optical emission-fluorescence technique, DLAS does not need a large solid angle of light collection -all information, which can be deduced from absorption signal, is "frozen" in a narrow laser beam of low divergence. Therefore the thermal emission of an investigated hot zone and laser stray light can be easily eliminated by a set of diaphragms and lenses. As a consequence, the hottest and most dense zones of an object can be probed by DLAS.

Electrically Driven Supersonic Combustion

“…Comparing schemes 1 and 2, it should be considered a significant benefit of scheme 1 at lean fueling whilst scheme 2 works at higher fuel injection rate, where scheme 1 demonstrates a petite thermal effect associated with fuel partial oxidation with excited species in air plasma. Such a two-stage mechanism of ignition was confirmed by TDLAS measurements [101,102].…”

“…The second pair of windows was located downstream with a distance of 65 mm between the two pairs of windows. The third pair of windows was used for post-flame zone observation and TDLAS measurements [101,102]. The instrumentation included the pressure scanner, the schlieren system, an optical emission spectrometer, current and voltage probes, a tunable diode laser absorption spectroscope (TDLAS) used for measurements of H2O vapor temperature and of concentrations, a five-component chemical analyzer, and high-speed cameras.…”

“…In scheme 1, electrodes are located upstream of the fuel injectors; plasma is generated mostly in air and then interacts with the injected fuel [16]. In scheme 2, electrodes are located downstream of the fuel injectors; the electrical discharge is generated in non-uniform air-fuel composition [101]. The fuel is injected through 5 circular (d = 3.5 mm) orifices all in a row across the span, as shown in Figure 8b.…”

“…The detailed data for the discharge dynamics and parameters were presented in Refs. [16,69,101]. An optical emission spectrum of the discharge, recorded from the plasma-fuel interaction zone at x = 20-30 mm, y = 0-10 mm, is shown in Figure 9.…”

Electrically Driven Supersonic Combustion

“…Comparing schemes 1 and 2, it should be considered a significant benefit of scheme 1 at lean fueling whilst scheme 2 works at higher fuel injection rate, where scheme 1 demonstrates a petite thermal effect associated with fuel partial oxidation with excited species in air plasma. Such a two-stage mechanism of ignition was confirmed by TDLAS measurements [101,102].…”

“…The second pair of windows was located downstream with a distance of 65 mm between the two pairs of windows. The third pair of windows was used for post-flame zone observation and TDLAS measurements [101,102]. The instrumentation included the pressure scanner, the schlieren system, an optical emission spectrometer, current and voltage probes, a tunable diode laser absorption spectroscope (TDLAS) used for measurements of H2O vapor temperature and of concentrations, a five-component chemical analyzer, and high-speed cameras.…”

“…In scheme 1, electrodes are located upstream of the fuel injectors; plasma is generated mostly in air and then interacts with the injected fuel [16]. In scheme 2, electrodes are located downstream of the fuel injectors; the electrical discharge is generated in non-uniform air-fuel composition [101]. The fuel is injected through 5 circular (d = 3.5 mm) orifices all in a row across the span, as shown in Figure 8b.…”

“…The detailed data for the discharge dynamics and parameters were presented in Refs. [16,69,101]. An optical emission spectrum of the discharge, recorded from the plasma-fuel interaction zone at x = 20-30 mm, y = 0-10 mm, is shown in Figure 9.…”

Electrically Driven Supersonic Combustion

“…Comparing schemes 1 and 2, it should be considered a significant benefit of scheme 1 at lean fueling whilst scheme 2 works at higher fuel injection rate, where scheme 1 demonstrates a petite thermal effect associated with fuel partial oxidation with excited species in air plasma. Such a two-stage mechanism of ignition was confirmed by TDLAS measurements [101,102].…”

“…The second pair of windows was located downstream with a distance of 65 mm between the two pairs of windows. The third pair of windows was used for post-flame zone observation and TDLAS measurements [101,102]. The instrumentation included the pressure scanner, the schlieren system, an optical emission spectrometer, current and voltage probes, a tunable diode laser absorption spectroscope (TDLAS) used for measurements of H2O vapor temperature and of concentrations, a five-component chemical analyzer, and high-speed cameras.…”

“…In scheme 1, electrodes are located upstream of the fuel injectors; plasma is generated mostly in air and then interacts with the injected fuel [16]. In scheme 2, electrodes are located downstream of the fuel injectors; the electrical discharge is generated in non-uniform air-fuel composition [101]. The fuel is injected through 5 circular (d = 3.5 mm) orifices all in a row across the span, as shown in Figure 8b.…”

“…The detailed data for the discharge dynamics and parameters were presented in Refs. [16,69,101]. An optical emission spectrum of the discharge, recorded from the plasma-fuel interaction zone at x = 20-30 mm, y = 0-10 mm, is shown in Figure 9.…”

Electrically Driven Supersonic Combustion

“…Comparing schemes 1 and 2, it should be considered a significant benefit of scheme 1 at lean fueling whilst scheme 2 works at higher fuel injection rate, where scheme 1 demonstrates a petite thermal effect associated with fuel partial oxidation with excited species in air plasma. Such a two-stage mechanism of ignition was confirmed by TDLAS measurements [101,102].…”

“…The second pair of windows was located downstream with a distance of 65 mm between the two pairs of windows. The third pair of windows was used for post-flame zone observation and TDLAS measurements [101,102]. The instrumentation included the pressure scanner, the schlieren system, an optical emission spectrometer, current and voltage probes, a tunable diode laser absorption spectroscope (TDLAS) used for measurements of H2O vapor temperature and of concentrations, a five-component chemical analyzer, and high-speed cameras.…”

“…In scheme 1, electrodes are located upstream of the fuel injectors; plasma is generated mostly in air and then interacts with the injected fuel [16]. In scheme 2, electrodes are located downstream of the fuel injectors; the electrical discharge is generated in non-uniform air-fuel composition [101]. The fuel is injected through 5 circular (d = 3.5 mm) orifices all in a row across the span, as shown in Figure 8b.…”

“…The detailed data for the discharge dynamics and parameters were presented in Refs. [16,69,101]. An optical emission spectrum of the discharge, recorded from the plasma-fuel interaction zone at x = 20-30 mm, y = 0-10 mm, is shown in Figure 9.…”