A. A. Zaitsev

Investigation of concentration limits of flame propagation in ammonia-based gas mixtures

The concentration limits of flame propagation inNH3-O2,NH3-H2-O2,NH3-O2-N2,and NH3-H2-O2-N2 mixtures at temperatures of up to70°C and pressures of up to1.0 MPa were studied experimentally. The lower concentration limit of propagation of ammonia flame in oxygen decreases significantly at elevated temperature and pressure, the effect of temperature being stronger than for organic combustible substances. It is shown that the Le Chatelier rule for the limits ofN2-NH3-O2 mixtures is satisfied with sufficient accuracy.

Investigation of the combustion characteristics of H2-O2-N2-H2O mixtures under elevated pressures and temperatures

The flammability limits and burning velocity of hydrogen-air mixtures with diluent (nitrogen, steam) have been studied experimentally at temperatures up to 250°C and pressures up to 4 MPa. It has been observed that the flammability limits are practically independent of pressure within 2–4 MPa. It is shown that nitrogen and steam as diluents have quantitatively and qualitatively different effects on the burning velocity of stoichiometric hydrogen-air mixtures. The effects observed are interpreted qualitatively.

Influence of the aerosol formed in the fast evaporation of superheated water on the combustion of methane-air mixtures in a closed vessel

The influence of the aerosol formed in the fast evaporation of superheated water at 150°C on the combustion of a methane-air mixture in a near-spherical closed vessel (volume 20 dm3) is investigated experimentally. The concentrational limits of flame propagation and the normal combustion rate are determined as a function of the mass concentration of the water aerosol. It is found that the flegmatizing ability of the aerosol is relatively low; it is not due to the formation of fairly large water drops but practically completely to the presence of saturated water vapor. Exponential reduction in normal combustion rate of the mixture with increase in concentration of the superheated-water aerosol is observed.

Flame propagation in hydrogen-air mixtures in a tube

The propagation of a hydrogen-air flame in a closed tube 76 mm in diameter and 2500 mm in length with and without a water film moving along the tube walls was studied experimentally and theoretically, it has been found that in a smooth-wall tube the maximum turbulization factor ranges between 10 and 30 for mixtures with the volume concentrations of hydrogen 15–30%. The presence of a moving water film on the tube walls intensifies the combustion process, which manifests itself in the essential acceleration of the detonation pressure rise. However, at the same time, the maximum explosion pressure for near-stoichiometric mixtures increases, while that for leaner compositions decreases. The results obtained are interpreted qualitatively.

Experimental study of the limiting conditions for diffusion combustion of gases and vapors in various media

Extinction conditions for diffusion flames of gases and vapors in various media were studied experimentally. The limiting blowout velocities of a diffusion jet when heated H2−N2 and H2−H2O mixtures flow out into air were found. The minimum fire-extinguishing concentrations upon diffusion combustion of gases (CH4 and C3H8) and liquids (A-76 gasoline) were measured.

ESTIMATION OF THE PRESSURE BUILT UP IN A NONHERMETIC VESSEL UPON COMBUSTION OF A SOLID-PROPELLANT COMPOSITION

We have developed an approximate mathematical model that allows one to calculate the pressure in a nonhermetic vessel upon combustion of a solid-propellant composition in it. Laboratory experiments showing the validity of the model were performed. It is shown that a maximum pressure is attained long before the combustion of the solid-propellant composition in a nonhermetic room.

Flameless combustion of hydrogen on the surface of a hydrophobized catalyst

The flameless combustion of hydrogen on the surface of a hydrophobized catalyst is investigated experimentally under various conditions. A quantitative interrelationship is discerned between the rate of catalytic oxidation of hydrogen and the catalyst surface temperature. It is shown that the presence of helium in the gas—air medium diminishes considerably the hydrogen oxidation rate by lowering the temperature of the catalytic surface by virtue of the high thermal conductivity of helium. An approximate mathematical model is proposed for the flameless combustion of hydrogen on the surface of a catalyst. It is shown that the insertion of catalytic rods in metal tubes of diameter 20 mm significantly enhances the performance of each element by the judicious direction of strong convection flows from the heated surface of the rod.