Vladimir A. Lozovsky

Absolute CH concentration in flames measured by cavity ring-down spectroscopy

Cavity ring-down spectroscopy (CRDS) was used to measure absolute concentration profiles of the CH radical in low-pressure methane/air flames. The Q1(4) rotational line of the C2Σ+←X2Π band at 315 nm was used for concentration measurements. Very high sensitivity (2×1010 cm−3) is demonstrated. The measured profiles are in good agreement with that calculated using the GRI-Mech mechanism.

Nonequilibrium concentrations of the vibrationally excited OH radical in a methane flame measured by cavity ring-down spectroscopy

Abstract Strong deviation from the Maxwell–Boltzmann equilibrium for the populations of the v ″=0 and v ″=1 vibrational levels of OH(X  2 Π i ) radicals was observed in the preflame zone of the methane/oxygen/nitrogen flame. The OH concentrations for the v ″=0 and v ″=1 levels were measured using cavity ring-down spectroscopy in the 30 Torr flat flame. In that flame the population ratio for v ″=1/ v ″=0 is ∼20 times the equilibrium value at locations ∼6 mm below the luminescent zone. Above the flame front this ratio was found to be close to the equilibrium value.

ABSOLUTE HCO CONCENTRATION MEASUREMENTS IN METHANE/AIR FLAME USING INTRACAVITY LASER SPECTROSCOPY

Intracavity laser absorption spectroscopy was used to measure the absorption spectra of a premixed, flat methane/air flame at a total pressure of 30 Torr. The spectra were measured in the spectral range of 16 000–16 300 cm−1. A flat flame burner was placed inside the cavity of a broadband dye laser pumped by a cw argon-ion laser. The spectrum of the laser output was measured by a high resolution spectrograph (with a spectral resolution of 0.003 nm). The spectrum of HCO radicals (A 2A′′←X 2A transition) was measured with a high signal-to-noise ratio at different positions above the burner, providing the first quantitative measurement of the absolute concentrations of the HCO radical in flames. The linewidths of the individual rotational lines in the spectrum can be closely fitted by the equation Γ=X+ZN2(N+1)2, where X=0.37±0.03 cm−1 and Z=(8±0.5)10−6. The rotational temperature of the HCO radicals was evaluated from the spectra, but the error and the data scatter are relatively high since the lines with a...

Radical concentration profiles in a low-pressure methane-air flame measured by intracavity laser absorption and cavity ring-down spectroscopy

Intracavity laser absorption spectroscopy (ICLAS) and cavity ring-down spectroscopy (CRDS) were used to measure temperature and concentration profiles in low-pressure (30 torr) methane/oxygen/nitrogen flames. Concentration profiles of the HCO and 1 CH 2 radicals were measured by ICLAS, whereas the OH radical profiles and temperature profiles were measured by CRDS. Flames with equivalence ratio =0.8, 1.0, and 1.2 were studied. HCO profiles and peak amounts agree well with model predictions based on the GRI-Mech 2.11 mechanism for the stoichiometric flame (=1.0). The absolute concentration of singlet CH 2 radical could not be determined accurately, because of large uncertainty in the absorption cross section of this radical. Nevertheless, the experimental singlet CH 2 concentration seems to be higher than predicted by model (by more than 20 times, based on the estimated cross-section data). The relative 1 CH 2 profile is very close to the prediction. The OH profiles agree well with model calculation: however, absolute experimental OH peak concentration is about two times lower than the predicted value.

Intracavity laser absorption spectroscopy measurements of CN using red system A–X. Simultaneous observation of CN, NH2, HNO and 1CH2 in low pressure hydrocarbon flames doped with nitrogen oxides

Abstract Absorption spectra of the CN radical have been measured by Intracavity Laser Absorption Spectroscopy in hydrocarbon flames doped with minor amount of nitrogen oxide. Spectra of the CN red band system ( A 2 Π← X 2 Σ + ) have been observed in the spectral range of 642 nm along with lines of other species from flame: NH2, HNO, 1 CH 2 , and NO2. The sensitivity of about 2.3×10 10 cm −3 at 1700 or ∼100 ppb at 30 Torr at 1700 K has been demonstrated.

Absorption spectroscopy measurements of NH and NH2 absolute concentrations in methane/air flames doped with N2O

Intracavity laser absorption spectroscopy (ICLAS) and cavity ring-down spectroscopy (CRDS) were used to measure concentration profiles of NH 2 and NH in low-pressure (30 torr) methane/oxygen/nitrogen flames doped with a small amount of N 2 O. High sensitivity of these absorption spectroscopy methods was demonstrated (4×10 10 cm −3 for NH and 8×10 10 cm −3 for NH 2 ). The absolute NH concentrations agree well with those predicted by the GRI-Mech 2.11 mechanism and one-dimensional PREMIX code. The absolute NH 2 concentrations in the lean flame are fitted well by the calculations, but in the stoichiometric and the rich flames, the observed concentrations are about twice that predicted. In the rich flame ( ϕ =1.2), the calculations underpredict the NH concentrations at large distances from the burner. The strongest difference was found for the NH 2 radical at large distances above the burner. The strong spectra of NH 2 were observed even at 40 mm above the burner where the model calculations predict very insignificant concentration of NH 2 . The observed discrepancy can be caused by limitations of both the chemical mechanism and one-dimensional PREMIX code used for calculations.

Intracavity laser absorption spectroscopy study of HNO in hydrocarbon flames doped with N2O

Abstract Intracavity laser absorption spectroscopy is used to monitor HNO and NO 2 spectra in hydrocarbon/air flames doped with nitrous oxide, N 2 O, at low mole fraction. Methane flames of different equivalence ratios are used. High-resolution spectra of HNO are recorded near 642–644 nm. Spectra are also recorded near 618 nm where the absorption cross-section is known from the literature. The HNO spectrum is observed only in the rich and stoichiometric flames, with absorption being almost independent of location in the flame. In the lean flames, the HNO spectrum disappears and the intense NO 2 spectrum forms instead.

Intracavity laser absorption spectroscopy of flames: concentration measurements of intermediate species

Intracavity laser absorption spectroscopy was used to study concentration profiles of several radicals in flames. Very high sensitivity of ICLAS enables quantitative measurements of absolute concentrations of atoms and radicals in flames. MOst of the experiments were done with a flat flame burner placed inside the cavity of a broad band dye laser. The spectra of HCO radicals and CH2 radical, in the singlet electronic state were measured with a high signal-to-noise ratio at different position above the burner.In this work we report the measurement of the concentration profiles of HCO and CH2 radical sin methane/air flame. The spectra of these two radicals can be measured simultaneously which is advantageous in combustion diagnostics. Cavity ring-down laser spectroscopy was used to measure the OH concentration profiles of the HCO and OH radicals are in reasonable agreement with computer simulation results. However, a rough estimation of the CH2 absolute concentration indicates a much higher concentration than that which can be predicted based on the model calculation.