Experimental Determination And Numerical Simulation For Radiative Properties Of Liquid Fuels At Various Temperatures

The radiative properties of liquid fuels play an important role in diagnosis and regulation of fuel combustion in thermal devices such as automobile engines,aerospace engines and liquid-fuel fired boilers.And the optical constants of the liquid fuels,as the basic material properties,is significant in some aspects including composition determination,droplet evaporation,optical diagnosis,combustion control.With emerging liquid fuels developing,the optical constants data is relatively deficient.Meanwhile,there are still some key problems to be studied in the application of radiation transfer related to optical constants.Therefore,the main purpose of this paper is to obtain accurate data of optical constants and radiative properties of liquid fuels by the experimental determination and numerical calculation.Thus,these data is applied to the calculation of radiative heat transfer in engineering.In this paper,the organic liquid fuels,n-octane and n-decane,are studied.Firstly,the experimental measuring system based on the improved ellipsometric reflection method of liquid optical constants determination is constructed.Then the optical constants of n-octane and n-decane at various temperatures and mid-infrared wavelength region are obtained experimentally,and the temperature effects on the optical constants are discussed.Secondly,the radiative properties of single droplet and droplets system are calculated based on the Mie theory.Then the numerical simulation of radiation heat transfer in the spray combustion process is completed by using the calculated radiative properties of droplets.And the effects of radiation transfer on the spray combustion are studied.The main tasks are listed below:In the measurement of optical constants of liquid fuels,the optical constants of liquid n-octane and n-decane are determinated by ellipsometry reflection method at the temperature 20?,50?,80? and 20?,60?,90?,120?,between the wavelength range 2~16?m,respectively.The results show that the variation tendency on optical constants of the n-octane and n-decane with wavelength varying are same,there is just some difference in value.The optical constants of liquid n-octane and ndecane show a decreasing tendency as temperature increases.With temperature increasing,the refractive index shows a tendency of liner decrease and the refractive index peak lowers obviously.By contrast,the effect of temperature on absorption index is much smaller,and even negligible.In the calculation of radiative properties of droplets,the scattering efficiency factor,absorption efficiency factor,scattering coefficient and absorption coefficient of the n-octane droplets with radius of 10?m,20?m,and 50?m are calculated by MATLAB programming based on the Mie scattering theory.It can been seen from the calculated results that the temperature effects on scattering efficiency factor are not in the same rule in the different wavelengths.But the temperature effect s on absorption efficiency factor are consistent with the absorption index,which the absorption efficiency factor decreases slightly with temperature increasing.In addition,as the droplet radius increases,the scattering efficiency factor of n-octane droplet shows regular damped oscillation characteristics.As for droplets with equal radius,the scattering is weaker,where the absorption is greater for a given wavelength.For the droplet system which is relatively sparse to satisfy the independent scattering conditions,the radiative properties of droplets system are the linear superposition of the single droplet.Therefore,the radiative properties of droplets system are proportional to the volume fraction of droplets.In the numerical simulation of radiative heat transfer in spray combustion,the spray atomization,combustion heat transfer and radiation heat transfer of liquid fuel in the combustion chamber,which the volume is determined,are studied by numerical simulation.The simulation results show that the difference of temperature field distribution whether the wall radiation and the droplet radiation considered is little.But the highest flame temperature is different.When the droplet radiation is considered,the spray combustion is more sufficient and the flame length increases.