Theoretical And Experimental Study On The Regularity Of Dissolved Gas Evolution From Domestic Jet Fuel

The aircraft fuel tank is prone to catch fire or explode and it is a serious threat to crew safety when there exist irreducible ignition sources.The study shows that fuel tank inerting technology is an economical and efficient way to reduce fuel tank flammability and ensure safety.Therefore,it is necessary to have a deeper understanding of the mass transfer behavior of gas in jet fuel,such as dissolution,diffusion and evolution for the optimization designing of fuel tank inerting system and reducing compensation loss.Aiming at the deficiency of fuel tank inerting technology,the experimental systems are set up to measure the solubility and mass diffusion coefficient of CO2,O2 and N2 in domestic jet fuel in equilibrium solution.CFD simulation method is applied to analyze the evolution characteristics of dissolived gas in jet fuel,and the influencing factors of gas-liquid mass transfer in scrubbing inerting system are discussed.The research on the inert mode of XX uav is conducted at the given flight package line to verify the feasibility of ground based inerting and the improvements are put foward.The main study and innovative relults in this paper are as follows:(1)An experimental platform for equilibrium solubility is set up with equivolumetric saturation method to measure the solubility of CO2,O2 and N2 in RP3 and RP5 jet fuel under low pressure at248.15 K ~ 323.15 K,the Ostwald coefficients are obtained and compared with the calculated date according to the general equations abroad.The experimental results show that the difference are great and the maximum deviation up to 28.34 %.It fully proves that the Ostwald coefficient obtained on the basis of foreign general equation is not suitable for domestic fuel gas dissolved quantity prediction.Therefore,the general equation is linear corrected with least square method and calculation equation for the Ostwald coefficient of domestic fuel physical property is proposed.The deviation of solubility between the theoretical calculation and experiment can be less than 5 %.(2)An experimental platform is establish to measure the mass diffusion coefficient of gas in jet fuel with method of digital holographic interferometry,and the self-programming for digital image processing is coded using Matlab software.The mass diffusion coefficient of CO2、O2 and N2 in RP3 and RP5 jet fuel at 278.15 K～343.15 K are measured and fitted with the Arrhenius equation.The maximum deviation between the calculation and experiment is 9.51 %.The relationship between mass diffusion coefficient of gas in fuel,viscosity and temperature is studied according to Stokes-Einstein equation and it is found that Dμ/T is not constant in gas-liquid diffusion system at different temperatures.Dμ/T increase with the increase of temperature and can be approximately expressed as a linear function of temperature.The Stokes-Einstein equation is modified with experimental data,and the deviation of mass diffusion coefficient between the calculated and experimental result is less than10 %.(3)CFD theory is proposed based on the basic rule of gas-liquid mass transfer.The oxygen concentration change with the stimulation in fuel tank is measured,and compared with the calculated result to verify the reliability of the calculation model.The evolution ruel of O2 and N2 from RP3 jet fuel in inert fuel tank under heating and decompression stimulation are studied.Under the heating stimulation,the oxygen concentration in ullage is less affected by the temperature,but more affected by the fuel load and the initial oxygen concentration in ullage.The oxygen concentration increment in ullage can reach maximum 5.92 % with the heating temperature 343 K,fuel load 70 %,and initial oxygen concentration 6 % in ullage.Under the pressure reduction stimulation,the initial oxygen concentration in ullage has little influence on the change of oxygen concentration,while the pressure and fuel load have great influence on the change of oxygen concentration.The maximum variation value of oxygen concentration in ullage can reach 12.4 % with pressure 20 kPa,fuel load 70 %,and initial oxygen concentration 6 % in ullage.The prediction models of time constant of dissolved oxygen evolution from fuel under stimulation are proposed according to calculation,and the maximum deviation is 4.77 % for heating stimulation,and 5.02 % for decompression stimulation.(4)The factors influencing the mass transfer of O2 and N2 between the gas and liquid phases during tank scrubbing inerting is studied with the Eulerian-Eulerian double fluid model.The results show that the larger the bubble diameter,the smaller the gas-liquid mass transfer rate,the smaller the volume mass transfer coefficient of oxygen and the higher the time constant during the scrubbing inerting.The higher the superficial gas velocity at the inlet of nitrogen enriched air,the higher the gas-liquid mass transfer rate,the higher the volume mass transfer coefficient of oxygen and the lower the time constant of scrubbing.The higher the fuel load,the lower the gas-liquid mass transfer rate,the smaller the volume mass transfer coefficient of oxygen and the higher the time constant of scrubbing.(5)The feasibility of the ground based inerting for tank protection of XX uav is analyzed by CFD.The ground based inerting can not meet all the requirements of fuel tank inerting at the given flight line.An improvement scheme of reverse scrubbing inerting is proposed for ground scrubbing inerting and nitrogen filled protection is proposed for ground washing inerting.The improved scheme can meet the requirements of fuel tank inerting.Compared with the onboard inert gas generation system,the ground based inerting generates less fuel compensation loss,and the improvement scheme of reverse scrubbing inerting for ground based inerting has more advantages on performance and application.