Experimental investigation of atomized water droplet initial parameters influence on evaporation intensity in flaming combustion zone

Quantitative research on gas explosion inhibition by water mist

Suppression effects of ultrafine water mist on hydrogen/methane mixture explosion in an obstructed chamber

Experimental research on the characteristics of methane/air explosion affected by ultrafine water mist.

Explosion behaviors of mixtures of methane and air with saturated water vapor

Experimental and numerical investigation of flame speed retardation by water mist

The roles of the physical, thermal and chemical effects of fine water droplets on extinguishment of diffusion flame subjected to high strain are quantified experimentally using a methane counterflow diffusion flame. Water droplets were generated by twin-fluid atomizers and ultrasonic mist generators. The distributions of water droplet diameter were measured by a PDPA and found to be nearly normal, with the number mean diameter ranging typically from 15 to 25 μm and the Sauter mean diameter from 25 to 30 μm. The limit of extinguishment was determined by the velocity gradient and the non-dimensional fuel-ejection velocity. The critical velocity gradient at extinguishment without water droplets was found to be 423 s −1 . Introduction of water droplets into air stream resulted in reduction of the velocity gradient at extinguishment due to evaporation which causes the cooling and depletion of oxygen in the flame zone. The critical velocity gradient at extinguishment decreases with the increase of the surface area parameter, Σ , which is expressed by the ratio of mass fraction of water droplets to Sauter mean diameter. By a simple analysis, the lifetime of a droplet was compared with the residence time and it was found that there exists threshold below which droplets can be evaporated within the flame zone. PDPA measurement also showed that the water droplets with diameters larger than the threshold pass through the flame zone towards the stagnation plane. The threshold was found to depend on the velocity gradient. The maximum temperature measured by a thermocouple decreases with the mass loading of water droplets as well as the velocity gradient. However, the maximum temperature at extinguishment is rather independent of mass loading of water droplets and also of velocity gradient and the thermal effect is predominant in the extinguishment of the counterflow diffusion flame.

Effect of fine water droplets on extinguishment of diffusion flame stabilized in the forward stagnation region of a porous cylinder

In the present study, extinguishment of propane/air co-flowing diffusion flame by fine water droplets was investigated experimentally. Water droplets are generated by piezoelectric atomizers with the maximum droplets flow rate of 1500 ml/h. When the fuel injection velocity Uf is low, an attached laminar diffusion flame with a premixed flame at the base is stabilized. At some distance from the burner rim, a transition from laminar to turbulent diffusion flame occurs, and a turbulent diffusion flame is formed in the downstream region. When the fuel injector rim is thin (δ = 0.5 mm), the flame stability deteriorates with increase of the co-flowing air stream velocity Ua and the water droplets flow rate Qm. The stability mechanism can be explained by the balance of the gas velocity and the burning velocity of premixed flame formed at the base. However, when the injector rim is thick (δ = 5 mm), a recirculation zone is produced downstream of the injector rim. The dependence of the quenching distance Hq on Uf and Qm is relatively weak, and the stability diagram shows curious features. It was shown that Ua is crucially important since it determines flow residence time; if Ua   0.4 m/s, the water droplets should pass by the recirculation zone without sufficiently evaporated and are not so effective to extinguish the flame. The supply velocity of droplet-laden air should be low enough so that water droplets can evaporate and water vapor can diffuse into the premixed region at the base to obtain sufficient effectiveness of water droplets for fire suppression.

Extinguishment of propane/air co-flowing diffusion flames by fine water droplets

Extinguishment of counterflow methane/air diffusion flame by polydisperse fine water droplets

Experimental study of suppressing effect of fine water droplets on propane/air premixed flames stabilized in the stagnation flowfield

Hiroyoshi Naito

Papers

Experimental and numerical investigation of flame speed retardation by water mist

Effect of fine water droplets on extinguishment of diffusion flame stabilized in the forward stagnation region of a porous cylinder

Extinguishment of propane/air co-flowing diffusion flames by fine water droplets

Extinguishment of counterflow methane/air diffusion flame by polydisperse fine water droplets

Experimental study of suppressing effect of fine water droplets on propane/air premixed flames stabilized in the stagnation flowfield