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ATOMIZATION OF LIQUID FUELSCOMBUSTION AND FUELSTHE PRINCIPLE OF LIQ UI DS ATOMIZATIONAtomization is the processwhereby bulk liquid is transformed into acollection of drops.This transformation goes throughthe break-up of liquid jet into a numberof filaments, which in turn transform intodroplets.COMBUSTION AND FUELSMECHANISMS OF LIQU I DS ATOMIZATION Three mechanisms:Disintegration of a liquid jet into a number of filaments, and then into small droplets, requires the surface tension forces of liquid to be overcome. It may happen on the three ways:–by surface tension between moving liquid jet and steady air which destabilise the jet and causes its disintegration into filaments,–by centrifugal forces of swirled liquid jet,–outer mechanical and electrostatic forces and by supersonic acoustic.COMBUSTION AND FUELSFLUID ATOMIZATION WITH DIFFERENT ENERGYCOMBUSTION AND FUELSJETS DISINTEGRATION AND DROPLETS BREAKUPPrimary liquid jetdisintegrationDroplets break-upCOMBUSTION AND FUELSRANGE OF LIQUID ATOMIZATIONRe = (UL)/νWe = (U2L)/σσ-the surface tensioncoefficientCOMBUSTION AND FUELS5 bars10 bars15 barsTORCH OF PLAIN-ORIFICE ATOMIZED OILCOMBUSTION AND FUELSLIQUID SHEET BREAKUPSwirled jetCOMBUSTION AND FUELSTYPES OF OIL INJECTORS/ATOMIZERSTypes of atomizers:-pressure-pneumatics-rotating plain-orifice swirl typeY typewith x-cross shape flowCOMBUSTION AND FUELSPRESSURE INJECTORS COMBUSTION AND FUELSPLAIN-ORIFICE ATOMIZER> 0.5 mmDo∆p = 0.3-1(5) MPaα= 5-15oSimple construction,Low quality of atomizationCOMBUSTION AND FUELSSWIRL ATOMIZERS COMBUSTION AND FUELSHOW A SWIRL NOZZLE WORKS COMBUSTION AND FUELSSWIRL NOZZLE:DESIGNd= 2-6 mmo∆p = 0.6-1.0 MPaα= 45-90oSimple constructionHigh reliabilityHigh quality of atomizationLow energy consumptionCOMBUSTION AND FUELSSWIRL NOZZLE: AN EXAMPLE COMBUSTION AND FUELSCOMPACT SWIRL ATOMIZER COMBUSTION AND FUELSTYPE OF FUEL CONESDelavanCOMBUSTION AND FUELSSWIRL ATOMIZER IN OPERATIONDispersed oil jetCOMBUSTION AND FUELSPNEUMATIC ATOMIZERS COMBUSTION AND FUELSCOMBUSTION AND FUELS PNEUMATIC ATOMIZER: PRINCIPLE OF OPERATIONConsumption of atomizing medium:δ=0.06-0,1 kg/kgatomizing mediumair / steamrecirculating small dropletsair jetlayer of fuel around theatomizing mediumabout 5 x diameter ofatomizing nozzleabout 40 x diameter ofatomizing nozzleliquid fuel small droplets formedoutside of the stream dispersion of the streamsmall droplets formedfrom the stream big droplets formed fromthe disintegration of thestreamdeformation wave of fuelPNEUMATIC ATOMIZER OF Y TYPE Pneumatic atomizer of Y type:1 –oil,2 –gas,3 –atomizing head,4 –nozzlesCOMBUSTION AND FUELSPNEUMATIC ATOMIZER OF CROSS-SHAPE FLOW TYPE Pneumatic atomizer of the cross-shape flow type:1 –oil,2 –gas,3 –oil injection,4 –gas injection,5 –mixing chamber,6 -nozzlesCOMBUSTION AND FUELSROTATING ATOMI Z ERS COMBUSTION AND FUELSOIL BURNER WITH ROTATING ATOMI Z ERCOMBUSTION AND FUELSCONTROL OF OIL FLOW RATECOMBUSTION AND FUELSATOMIZATION PRESSURE VARIATION 1.The simplest way for oiloutput/consumption control is variation of pressure of atomization.2.Disadvantage of this method of outputcontrol is loss of atomization quality due to reduction of atomization pressure.Rate of oil output ∼(∆p)0.5COMBUSTION AND FUELSTwo-step control of oil flow rateScheme of single chamber two-step oilatomizer:1 –valve, 2, 3 –recalculating pipesCOMBUSTION AND FUELSCOMBUSTION AND FUELS CIRCLE MECHANICAL (RETURN-FLOW) ATOMIZER Fuel nozzleOil tankNozzle Pump ValveCIRCLE OIL ADJUSTING VALVE1 –VALVE,2 –SWIRL CHAMBER,3 –OIL CIRCLE HOLESCOMBUSTION AND FUELSTWO-NOZZLES ATOMIZERI –nozzleII -nozzleCOMBUSTION AND FUELSQUALITY OF ATOMIZATION COMBUSTION AND FUELSPARAMETERS OF ATOMIZATION–output,kg/s–angle of dispersion, deg–droplets distribution,–mean diameter of dispersion, m.COMBUSTION AND FUELSCHARACTERISTICS OF ATOMIZING NOZZLECOMBUSTION AND FUELSOUTPUT of PRESSURE ATOMIZERSOutput m of pressure atomizers is defined as follows:∆p)0,5m= µA(2ρcwhere: A is the area of the nozzle output,p is pressure and µis the outflow coefficient.COMBUSTION AND FUELSDROP SIZE DISTRIBUTIONDrop sizedistribution curves COMBUSTION AND FUELSCHARACTERISTIC OF DROPLETS SIZEMean drop size:mean drop sizeMDS= [(ΣnD3/ΣnD)]0,5,Sauter mean drop sizeSMDS= ΣnD3/ΣnD2.COMBUSTION AND FUELS。
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西北工业大学
航空发动机燃烧学课程组
《航空发动机燃烧学》
雾化特性参数
CONTENTS
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1雾化细度
2液滴尺寸分部
3雾化锥角
4雾化均匀度
5流量密度分布
6雾化射程
质量中间直径(MMD d
m )
1
•液雾中大于这一直径的所有液滴的总质量恰好等于小于这一直径的所有液滴的总质量；
•MMD越小，真实液雾中的小颗粒所占的比例越大
雾化炬颗粒尺寸分布特性曲线
d m与d32可能存在很大的差别，它
们之间存在一定的关系。
•雾化细度并不是越小越好。
•对于强化燃烧过程，雾化过细，
马上被气流带走，在某一区域形
成过浓的混合物；而在油滴无法
喷射到的地方，混合物的浓度却
很稀。
要求液滴直径在20~200 µm之间，且液滴的中间直径不大于75~100 µm
液滴的尺寸分布。
