| In view of the rapidly increasing demand for alternative aviation fuels in civil aviation,there is an urgent need to find suitable alternative fuels to solve the problem of energy scarcity in the air transport sector.China is rich in coal resources,and coal direct liquefaction jet fuel is superior to petroleum-based jet fuel in terms of density,low-temperature performance and thermal stability,and has the potential to become a high-quality aviation alternative fuel.Currently,there is a lack of advanced theoretical support for aviation alternative fuels in terms of ignition and combustion characteristics and their pollutant emission characteristics for airworthiness certification.Based on this,this thesis takes Direct coal liquefaction（DCL）and RP-3 aviation kerosene（RP-3 jet fuel）,which are unique to China,as the research objects.A detailed experimental study of the soot generation characteristics of the three coals was also carried out.The variation of Ignition Delay Times（IDTs）,Induction Delay Times（IDTs）and Soot Yield（SY）of RP-3 coal and its blended coal with DCL at 30%DCL+70%RP-3 and 70%DCL+30%RP-3 by volume(hereinafter referred to as 3/7 blend jet fuel and 7/3 blend jet fuel at different temperatures,pressures and equivalence ratios were systematically investigated.The results can be used to build a standardized database for aviation alternative fuels,improve the combustion and emission characteristics of DCL,and provide data support for the airworthiness validation and commercial application of DCL:（1）The ignition delay times of RP-3 jet fuel,3/7 blend jet fuel and 7/3 blend jet fuel at different pressures（3.0,10.0 bar）and equivalence ratios（0.5,1.0,2.0）were measured over a wide temperature range（1000-2000 K）using a surge tube experimental system.The effect of pressure,temperature and equivalent ratio on the ignition characteristics of each of the three fuels was examined in detail.On this basis,the experimental results were fitted in Arrhenius form to obtain the dependence of the ignition delay time on the initial ignition pressure,temperature,equivalence ratio and fuel and oxygen concentrations for each of the three fuels.The experimental results show that the reactivity of the three coals increases with increasing ignition pressure at constant equivalence ratios,as evidenced by the shortening of the ignition delay time with increasing pressure.At constant pressure,the ignition delay times of RP-3 jet fuel and 3/7 blend jet fuel at low pressure（3.0 bar）were less affected by the equivalence ratio,while the ignition delay times of 7/3 blend jet fuel showed a tendency to increase with increasing equivalence ratio.At high pressure（10.0 bar）,the ignition delay time for all three coals decreased with increasing equivalent ratio.In addition,by comparing the ignition delay times of the three coals under the same ignition conditions,it was found that the ignition delay times of the 3/7 blend jet fuel and 7/3 blend jet fuel were greater than those of the RP-3 jet fuel at low pressure,while the ignition delay times of the three aviation coals were very similar when the pressure was increased to 10.0 bar.（2）Based on the physical properties and chemical composition of the fuels,three-component models for RP-3 jet fuel and five-component substitution models for 3/7 blend jet fuel and 7/3 blend jet fuel were developed respectively.Detailed chemical kinetic simulations of the ignition process of the three aviation coals under different initial conditions were carried out using Chemkin Pro software using the existing detailed combustion chemical kinetic mechanism including 793 species and 4358 radical reactions.The simulation results showed that the model predicted results and experimental results under high pressure（10.0 bar）low temperature conditions showed good agreement The results of the simulations show that the model predictions at high pressure（10.0 bar）and low temperature are in good agreement with the experimental results,but the model predictions at high temperature are low;the model predictions at low pressure（3.0 bar）are lower than the experimental results.（3）Detailed kinetic analysis of chemical reactions was performed for the ignition and combustion processes of the three fuels.The results of sensitivity analysis show that the fundamental reactions that play a key role in the combustion of the three aviation coals are basically the same.The most important reaction for ignition promotion is H+O2<=>O+OH and the most important reaction for ignition inhibition is HO2+OH<=>H2O+O2.The radical reactions of ignition process are very sensitive to temperature,and only the large molecule hydrogen extraction reactions will play a role in ignition process at low temperature,while most of the radical reactions that play a role in the ignition become small molecule radicals as the temperature increases.As the temperature increases,most of the radical reactions that contribute to ignition become reactions between small molecule radicals.（4）Using a laser absorption device equipped with a radical tube experimental system,the carbon soot induction delay times and carbon soot yields of three types of aviation coals were measured at different pressures（3.0,6.0 and 10.0 bar）and equivalence ratios（20.0 and∞）over a wide temperature range（1900-2500 K）.The experimental results showed that the carbon soot induction delay times of the three coals decreased with the increase of temperature and pressure in the overall trend and increased with the increase of the equivalent ratio.it can be found that there is a critical temperature for the soot induction delay time of all three coals,above the critical temperature,the soot induction delay time shows a trend of 7/3 blend jet fuel>3/7 blend jet fuel>RP-3 jet fuel,and below the critical temperature,it shows the exact opposite trend.In addition,the carbon soot yield measurements show that the overall trend for all three fuels increases with increasing pressure and with increasing equivalent ratio.The soot yields of the three fuels showed a trend of increasing and then decreasing with temperature,showing a typical Gaussian curve distribution. |
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