| As the oil supply is increasingly tight, the study on alternative clean fuel receives the increasing attention. Ethanol, as a renewable clean oxygen-bearing biofuel, and with the help of cosolvent for the preparation of ethanol-diesel fuel, will has the broad application prospect in the diesel engine. As the diesel engine are to developed into the clean, efficient and low CO2emission, it is necessary to look into the details of atomization combustion of multicomponent fuel ethanol diesel fuel in cylinder, and to realize the optimized matching of "fuel oil supply system and alternative fuel, inlet system, structure parameter of combustor" by using the physicochemical property of fuel and core boundary conditions to conduct the optimal control of combustion path. Based on physical property calculation of multicomponent fuel, ethanol diesel fuel single-droplet evaporation model, the analysis on mass and heat transfer, and the turbulent diffusion combustion model, the fuel physical property parameter library and diesel atomization and combustion modules of internal combustion engine’s in-cylinder fluid dynamics simulation software (ICFD-CN) are improved, FORTRAN language is used to write the underlying code, the multicomponent fuel atomization and combustion simulation platform is built, and laser atomizing test bed and bench test are used to verify the reliability of the simulation platform. With YZ4102ZLQ engine as the object, the study on the influence mechanism of ethanol diesel fuel property on spray and combustion is carried out by using the numerical calculation and experiment, and the main contents are as follows:(1) The real-time dynamic calculation of physical property parameter of mixed fuel is carried out. For ethanol-diesel fuel, the mass fraction of components in the process of droplet evaporation is constantly changing, and the empirical formula shall be used to calculate physical parameters. Empirical formula is chosen to estimate the surface tension of liquid, evaporation enthalpy and thermal conductivity, viscosity, density, saturated vapor pressure and standard enthalpy of formation of tetradecane, ethanol and n-butyl alcohol, as well as the diffusion coefficient of n-butyl alcohol vapor in the air, the calculation results obtained from empirical formula shall be compared with the reference value, and according to the difference of estimated value and experimental value, the empirical formula of the thermal conductivity and viscosity were corrected for high estimation precision.(2) The evaporation model of the single droplet of multicomponent fuel was built, and the influence of fuel property on the evaporation process was carried out. Droplet evaporation is an important stage of in-cylinder fuel evaporation and atomization of diesel engine, and ethanol-diesel(diesel fuel is considered as the one-component) is composed of the components with bigger difference of physicochemical property, which is different from the single-droplet evaporation of diesel. According to the difference of physicochemical property between ethanol and diesel(boiling phenomenon can’t be ignored) under the high-temperature, high-pressure and strong-vortex environment of engine and small high-pressure injection atomization droplets, the distillation curve model and boiling evaporation coupling model are put forward to describe the droplet’s mass and heat transfer process of ethanol-diesel, and references are used to verify the feasibility of model. Combined with boundary condition of diesel engine, the influence rules of mass and transfer process during droplet evaporation is investigated.(3) Flame surface model with great engineering application prospect is used to calculate the turbulent diffusion combustion rate. According to the property of multicomponent fuels of ethanol-diesel, the control equation was added, and the basic equation of flame surface model was extended to calculate the turbulent diffusion combustion rate of ethanol-diesel.(4) Based on ICFD-CN, atomization and combustion platform of multicomponent fuel was established.①ccording to the grid cell temperature and pressure, the revised physical property formula was used to improve the calculation code of property value in the modules such as fuel, evap, colide, lawall, chem and chemeq in ICFD-CN software;②The evaporation model of multicomponent fuel combined with evaporation code were written to replace the original evap evaporation module of ICFD-CN, meanwhile, the related code of other submodules was written, which help conduct the auxiliary calculation of atomization and evaporation;③Two-step reaction kinetics premixed combustion model generated by CO and CO2and diffusive combustion model of multicomponent fuel shall be further combined. Writing programs and improving chem, chemeq and rinput module are to build the atomization and combustion simulation platform of ethanol-diesel. With YZ4102ZLQ diesel as object, the laser atomizing test and bench test were used to verify the atomizing process, in-cylinder pressure and NOx emission. The results show that the calculated value is consistent with the experimental value, and can be further applied to the numerical investigation on spray and combustion process of ethanol-diesel engine. The construction of such platform break through the limitations of the original ICFD-CN program failed to predict the spray and combustion process of ethanol-diesel, which is of important reference value for the combustion process simulation of mixed fuel with bigger differences in physicochemical property.(5) Analysis on the influence of ethanol-diesel’s property on the injection and spray process was conducted. The nozzle end and pump end pressures of high pressure pipe of YZ4102ZLQ engine fueled with tetradecane and N5E10was measured, and the influence of fuel characteristics and engine load on fuel pressure wave property inside the high-pressure oil pipe were analyzed. Around the sensitivity of fuel property of ethanol-diesel to the primary atomization of continuous jet flow, and secondary atomization of droplet, and secondary atomization characteristic parameter to droplet radius, in-cylinder fuel evaporation rate, gas phase flow field and atomizing change, the influence of fuel property on atomization were analyzed in details, and it is concluded that the combustion of ethanol diesel fuel will further increase the vortex pulsation in the balance area balance area, but exerting little effect on the vortex motion. Meanwhile, the reasons of the in-cylinder atomization effect of N5E10better than that of tetradecane was explored. (6)The bench test was used to carry out the sensitivity research of the combustion and emission characteristics of ethanol-diesel to the cosolvent. The changes of cylinder pressure, rate of heat release, premixing and diffusive combustion duration, distribution of heat quantity, center of combustion, emission and particle size distribution of particulate matter from ethanol-diesel and diesel without changing structure parameter of diesel engine wereobtained. Compared with diesel, ethanol-diesel’s premixed combustion period is shorten that proportion of heat quantity in premixed combustion phase, diffusion combustion period is also shortens, and the center of combustion get close to the top dead center. NOx and smoke intensity of B10E10and N5E10were reduced, and N5E10is better. The distribution peak of exhaust particulate from ethanol-diesel moves to small size, and the variety of cosolvent is associated with combustion particle size distribution of ethanol-diesel. Compared with N5E10, the mass fraction of small size of particulate is further increased.(7) With the built simulation platform, the influence of fuel property of ethanol-diesel on combustion process was conducted. The influence of fuel property on evaporation rate of fuel, mixture distribution, fuel concentration field, temperature field, ignition delay period and combustible mixture quantity produced during the ignition delay period, fuel’s mass burning rate and concentration of key components in combustion process was obtained. The ethanol-diesel will improve the combustion stability, make temperature distribution more uniform and local high-temperature area decrease, and shape of high-temperature area turns from long and narrow distribution to the blocky distribution. During combustion of tetradecane and N5E10, the combustible mixture quantity produced in the ignition delay period is associated with the judgment of starting point of the start timing of combustion. Compared with tetradecane, the in-cylinder instantaneous mass burning rate of N5E10in the ignition moment will slightly lower, mass burning rate in the premixed combustion phase is associated with load, and burning rate in the diffusion phase will increase. |
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