S. Yu. Fedorov

Substantiation of the probe mass-spectrometric method for studying the structure of flames with narrow combustion zones

This work is devoted to the substantiation of the probe method for the case when the ratio of the width of the combustion in the flame to the outer diameter of the sampler tip is close to unity. It is precisely this value of the ratio that was used in the probe mass-spectrometric study of the structure of an ammonium perchlorate flame. A flat flame of the mixture 8% methane + 80% air + 12% argon was stabilized at atmospheric pressure in a flat burner. The authors measured the temperature distribution in the flame by a microthermocouple method. The measurement of the distribution of the methane concentration in the flame was done by mass-spectrometry. The authors measured the distributions of the absolute methane and nitrogen concentrations in the flame using a spectrometer with intracavity spontaneous Raman light scattering. The authors conclude that the data (v=0.3 and 1.2 mm/sec) were obtained under quasistatic conditions and the conclusions drawn regarding the heat flows from the probe to the combustion surface, obtained from analysis of the stationary methane flame, can be applied to them.

Measurement of Temperature and Concentration of OH Radicals in Combustion of Hydrogen and Ethanol by the Laser‐Induced Fluorescence Technique

Diffusion combustion of ethanol and hydrogen and homogeneous combustion of hydrogen–oxygen mixtures are studied by the laser‐induced fluorescence technique in the linear regime and with signal saturation. Data on the flame temperature and OH concentration are obtained. The burning temperature of 3090 K for a stoichiometric O2–H2 mixture is in agreement with the known value. It is shown that the maximum concentrations of radicals in the hydrogen–air and stoichiometric hydrogen–oxygen flames are close to each other (4.4· 1016 cm-3).

Heat and mass transfer and stabilization of combustion in the boundary layer behind a rib and a backward-facing step

A comparison of the characteristics of the boundary layer with combustion with flame stabilization by a rib and a backward-facing step is performed. Data on the thermal boundary layer, the flame blow-off velocity, and the rate of ethanol evaporation into an air flow with a turbulence intensity of up to 26% are obtained. It is shown that the temperature of the outer region of the boundary layer and the flame blow-off velocity behind the rib are higher than those behind the backward-facing step. With both methods of flame stabilization, the intensity of evaporation corresponds to transient mass transfer.

Ratio of rotational Raman cross sections for oxygen and nitrogen measured in air

Simulated and experimental spectra of spontaneous Raman scattering of oxygen and nitrogen in air are examined and compared. The experimental spectra were recorded during excitation by pulse lasers with the use of the broadband detection system. The new ratio of the rotational Raman intensity factors for O2 and N2 is found equal to (2.27 ± 5)%.

Temperature and OH Concentration Measurements in Alcohol–Air Flame Using Laser-Induced Fluorescence

Temperatures and OH concentrations in ethanol flames were measured using laser-induced fluorescence and probe methods. The maximum temperatures recorded by different methods agree with each other. During combustion of ethanol evaporating from the surface of a sphere 15 mm in diameter, the radical concentration was ≈ 7 · 1016 cm-3 taking into account fluorescence extinction. In concentration measurements, the equipment was calibrated in experiments with a hydrogen flame, for which these data are known. It has been established that in both cases, the maximum of the OH concentration is displaced with respect to the temperature maximum. The data obtained can be useful in studying the combustion of liquid fuel drops.

Measurement of the Combustion Temperature of a Solid Propellant by the Cars Method

To measure the solid‐propellant combustion temperature, a procedure was used based on examination of the temperature dependence of the Q‐branch of the coherent anti‐Stokes Raman scattering (CARS) spectrum due to nitrogen contained in combustion products. The measurements were carried out at a pressure of 4 MPa, under which the spectrum demonstrated a substantial overlap between spectral lines. CARS intensities at two frequencies were registered; their ratio was used to determine the combustion temperature of a stoichiometric ammonium dinitramide–polycaprolacton mixture.

A multipass optical scheme for broadband measurements in Raman-scattering spectra

An optical scheme that provides multiple transmission of a probing laser beam through an object under study is considered. A Raman-scattering (RS) spectrometer is described in which this scheme is used to increase a signal in local simultaneous measurements of the temperature and the composition of gaseous mixtures. Broadband RS spectra in gaseous jets in the presence and absence of combustion were obtained as a result of broadband recording. The results of their processing using original software tools are demonstrated.

Condensation of monosilane-argon and monosilane-helium mixtures in free jets

Condensation of gaseous monosilane-argon and monosilane-helium mixtures was investigated in free jets by a Rayleigh scattering laser diagnostic technique. The condensation of a SiH4-Ar mixture begins to develop at a lower stagnation pressure and at a shorter distance from the nozzle, and proceeds at a higher rate, as compared to condensation in monosilane-helium and pure argon jets. The results of Rayleigh scattering measurements in condensing monosilane-argon jets scale with the parameter P0d0.8. An analysis of the results obtained in this study and found in literature suggests that simultaneous monosilane-argon condensation lead-ing to the formation of mixed clusters takes place in the monosilane-argon mixture.

Simultaneous temperature and concentration measurements in hydrogen-air flames using a cars spectrometer

A relatively simple CARS spectrometer has been designed taking advantage of the pure rotational spectra of hydrogen. The spectrometer was used for simultaneous measurement of instantaneous temperatures and concentrations of fuel in hydrogen jets and flames with a high spatial resolution. Data on the fluctuation structure of the flow are reported.