Experimental Measurement Of The Optical Constants Of Liquid Fuels Under Heating And Pressing

At present,the new fuels such as methanol gasoline,ethanol gasoline and biodiesel have been developing vigorously,the numerical simulation of fuel combustion process is further improved.The radiation characteristics of liquid fuels in the visible and infrared bands are important parameters for the modeling and analysis of high temperature combustion processes in liquid fuel engines and thermal devices.The accuracy of the optical constants has important implications for liquid fuel ignition,combustion process diagnosis and regulation,fuel composition measurement and analysis.However,the optical constant data of various fuels are very scarce,especially under high temperature and high pressure conditions.In this paper,based on the experimental platform of the ellipsometer,the measurement system for liquid radiation properties and the reflective liquid sample cell are designed.The system can achieve the temperature from room temperature to 300 ? and the pressure from the normal pressure to 1.0 MPa range of arbitrary regulation.Experiments show that the temperature control accuracy can reach 0.5 ?,the pressure control system has good stability and sealing,the natural pressure drop per hour is only 0.07 MPa,and the pressure is adjustable at any time.The numerical simulation of the heating and deformation of each part of the sample cell was carried out.The maximum deformation of each part was not more than 0.02 mm,and the internal temperature distribution of the sample cell was uniform under different heat source conditions.On the basis of this,the system was verified and the optical constants of several liquids under different conditions were measured by reflection method and transmission-reflection combining method.In the aspect of reflection measurement,a mathematical model of reflection measurement was established.The optical constants of methanol,ethanol,palm oil and palm oil type biodiesel were measured by reflection method.The results show that the maximum difference between the refractive index of methanol at 20 ? and 60 ? can reach 4%,and the maximum difference of absorption index can reach 40%.The maximum difference between the refractive index of ethanol at 20 ? and 60 ? can reach 5%,and the maximum difference of absorption index can reach 37.5%.The influence of pressure on the optical constant value of ethanol is very small compared with the influence of temperature.When the pressure of ethanol is 0.1 MPa and 0.5 MPa,the difference of refractive index is not more than 0.3%,and the difference of absorption index is not more than 0.01%.The maximum difference between the refractive index of the palm oil at 20 ? and 150 ? can reach 4% and the maximum difference in absorption index can reach 50%.The maximum difference between the refractive index values of biodiesel at 20 ? and 150 ? is 6.3% and the maximum difference in absorption index is 48%.Overall,as the temperature increases,both the refractive index and the absorption index are reduced.In the transmission-reflectance measurement,the mathematical model of the transmission-reflection method was established,and the optical constants of rapeseed oil and corn oil were measured.Before the experimental measurement,according to the reflectance error curve and the relative transmittance curve,the incident angle of the reflection measurement was chosen to be 40 degrees and the thickness of the liquid layer of the transmission measurement was chosen to be different depending on the spectral range.Measure the thickness of 113 ?m,260 ?m,373 ?m,1 mm,2 mm and 5 mm in the range of 1 ~ 8 ?m.The results show that the refractive index curves of the two edible oils are basically the same,but the rapeseed oil is slightly larger than the corn oil at the peak of 2.7 ?m,3.3 ?m,3.5 ?m and 4.3 ?m.At a trough of 3.4 ?m,4.1 ?m,4.6 ?m,the bottom of the index is slightly smaller than the corn oil.For the absorption index,the wavelengths of rapeseed oil and corn oil are slightly different from those at the trough.The difference in the optical constants of the two edible oils is that different edible oils have different saturated fatty acids and saturated fatty acids.These measurements can be used to analyze the composition of edible oils and to detect the quality of edible oils.