| In order to resolve two major problems of energy shortage and environmental pollution,searching for total or partial replacement of kerosene has been a hot research topic in the field of aviation.Ethanol,regarded as a clean and renewable oxygenated fuel,has the advantages of wide sources of raw materials,simple preparation process,and low price.Thus,it has received much attention.Meanwhile,the pressure-swirl nozzle is widely used as atomization device in the gas turbine and its performance has direct influence on combustion efficiency.Therefore,theoretical analysis and experimental study combined with numerical simulation were employed to study the effects of ethanol concentration on the spray characteristics of swirling conical liquid sheets for kerosene/ethanol blends by means of advanced optical instruments.In addition,this paper exhibited the spray characteristics(spray flow field,spray angle,discharge coefficient,breakup length,and drop size distribution,etc)of nozzles with different structure sizes.Considering the effects of back pressure,pressure drop,geometrical characteristic parameter,and inclination angles of tangential inlet,the empirical formulas of spray angle and discharge coefficient were built based on the experimental results,respectively.The main work is as follows:Firstly,a set of optical spray platform was built to investigate the spray characteristics of swirling conical liquid sheets discharging from pressure-swirl nozzle.This platform consists of fuel and air supply system,constant volume chamber,and optical instrument.Fuel supply system can provide a maximum injection pressure of 6 MPa.Constant volume chamber can withstand a maximum back pressure of 4 MPa.Optical instruments can measure spray morphology,droplet velocity field,and droplet size distribution,etc.Secondly,the effects of the pressure-swirl nozzle structure on the spray characteristics of swirling conical liquid sheets were investigated.Droplet velocity and spray angle of kerosene and K70E30(70%kerosene and 30%ethanol)were carried out under the three different nozzle orifice diameters.The results obtained showed that spray angle and droplet velocity were the biggest when the orifice diameter of nozzle equals 0.5 mm.From the data obtained by this study and Buckingham n theorem,a correlation of the spray angle and Reynolds number had been developed.In addition,the effects of tangential inlet with four inclination angles on droplet axial velocity,discharge coefficient,liquid-sheet spreading angle,breakup length,and droplet size were studied,in which keresone was taken as working fluid.Meanwhile,considering the effects of back pressure,pressure drop,geometrical characteristic parameter,and inclination angle of tangential inlet,empirical correlations of discharge coefficient and liquid-sheet spreading angle were regressed.It can be found that the smallest droplet size was produced when the inclination angle is 15°.Once more,the effects of different volume fractions of ethanol(0?30%)on the global spray characteristics of keresone/ethanol blends were investigated by analysis of discharge coefficient,spray angle,breakup length,and droplet size distribution.Firstly,the effect of ambient pressure on the discharge coefficient was analyzed through the formula of friction coefficient between air and liquid film in annular flow.At pressure drop of 1.0 MPa,the gap of discharge coefficients between without and with back pressure of 2.0 MPa was 2.1%.The experimental results showed that the discharge coefficient decreased as the ethanol concentration increased.Secondly,the spray angle of pressure-swirl nozzle became larger when the concentration of ethanol increased.However,the spray angles attained the maximum value and were independent on the ethanol concentration at pressure drop over 0.8 MPa.A new formula of the friction coefficient for kerosene/ethanol blended fuel was obtained by modified the friction coefficient for kerosene.In addition,the experimental results showed that the breakup length and droplet size decreased as ethanol concentration increased while the droplet velocity increased.When the pressure drop exceeded 0.8 MPa,the ethanol concentration had little effect on the droplet velocity magnitude and droplet size.Compared with the theoretical values of the breakup length,the calculation accuracy of values obtained by semi-empirical formula was improved by 6.83%on average.Lastly,the effect of ethanol concentration on the local spray characteristics was investigated.The liquid film thickness of kerosene/ethanol blended fuel at nozzle tip was obtained by numerical simulation combined with empirical formula.Taking the liquid film thickness as characteristic length,the surface wavelength and droplet size after primary breakup were processed through dimensionless method.The average difference between the experimental and theoretical surface wavelengths under the conditions of short-and long-wave regimes were 7.8%and 4.6%,respectively.In addition,compared with the experimental droplet size after primary breakup,the calculation accuracy of the values obtained from semi-empirical formula was 18.8%higher than that of theoretical values.The above conclusions can provide experimental data and theoretical guidance for adding ethanol into kerosene in the propulsion plant of gas turbine. |
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