Experimental Studies Of Effervescent Atomizers At Low Mass Flow Rate

Coal-fired power plants, consuming a great amount of fuel oil for ignition and stablecombustion of pulverized coal, play an important role in the fuel-saving area. Plasmaignition and tiny-oil ignition technology have been applied extensively in oil-efficient field,and have achieved significant positive results, but their oil-saving effect to inferior coal isfar from satisfactory. In this thesis, effervescent atomization technology of good sprayproperties is introduced to tiny-oil ignition system and experimental researches areconducted to study the atomization and combustion properties of effervescent atomizers,providing theoretical and practical basis for subsequent ignition research of pulverized coal.The atomization methods of liquid, the parameters that evaluate spray qualities and themechanism of effervescent atomization are described in the thesis. The effects of operatingconditions （ALR, injection pressure etc.） and the internal geometry of atomizers on theinternal structures of the gas-liquid two-phase mixture, which determines the spray qualitiessuch as particle size levels and velocity profiles are studied deeply. The results show thatthe particle size levels, the velocity profiles of the oil spray and the mixing of spray andsurrounding air influence the combustion of oil spray largely.Based on the theories of effervescent atomization, an effervescent atomizer withdifferent orifice exits is designed, combining with the status of the application of tiny-oilignition technology. The flow-rate characteristics and spray characteristics of the atomizer,including spray cone angle, drop size and velocity profiles downstream are experimentallystudied. A3D-PIV is also utilized to measure the velocity of the sprays. The results showthat, with the increase of ALR, the liquid flow-rate decreases gradually and the oil particlesbecome smaller; with an increase of atomizing gas, spray cone angle exhibits a tendency tofirst increase and then keep stable, the pressure of the mixing chamber also increases insome given range, which enhances the exploring of the gas core, leading to higher velocityof the oil particle in the spray. The combustion experiments of the sprays show that, higherALR in some given range enhances the mixing of oil flame and the surrounding air, thenprompts the combustion, leads to higher temperature in the combustion chamber and more thermal NO formed; at lower ALR, bigger oil particles are produced and the length of thespray flame increases, which causes more CO and SO₂formed along the flame; and thevery low oil flow-rate produces low fuel concentration below the minimum limit in themixture of oil vapor and air causing the flame to extinguish. All the studies indicate that theatomizer designed is of good atomization properties and combustion properties, making itsuitable for tiny-oil ignition technology replacing ordinary bubbly atomizer.