【作者】 胡鹏；

【导师】 孙平；

【作者基本信息】 江苏大学 ， 动力机械及工程， 2014， 博士

【摘要】 随着石油供需矛盾的不断加剧,代用清洁燃料的研究越来越受到重视。乙醇是一种可再生的清洁含氧燃料,借助助溶剂制备乙醇柴油,具有广阔的应用前景。随着柴油机向着高效、清洁和低CO2排放发展,需要深入了解多组分燃料乙醇柴油在缸内雾化燃烧行为细节,利用燃料的理化性质协同燃烧边界优化控制燃烧路径,实现“油、气、室”三者的优化匹配。围绕多组分燃料的物性计算、乙醇柴油单液滴蒸发模型和传质传热过程分析以及湍流扩散燃烧模型等基础理论开展研究,改进内燃机缸内流体动力学仿真软件(ICFD-CN)燃料物性参数库、雾化燃烧相关模块,运用FORTRAN语言编写底层代码,构建多组分燃料雾化燃烧仿真平台,利用激光喷雾试验和台架试验验证了仿真平台的可靠性。以YZ4102ZLQ柴油机为对象,结合数值模拟和试验开展了乙醇柴油燃料特性对雾化燃烧过程影响机理的研究。主要内容如下：(1)开展混合燃料物性参数实时动态计算。对于乙醇柴油来说,液滴在蒸发过程中各组分质量分数在不断发生变化,需采用经验公式计算物性参数。选取经验公式预测对十四烷、乙醇和正丁醇的液体表面张力、蒸发焓、液体热导率、粘度、密度、饱和蒸气压、标准生成焓以及正丁醇蒸气在空气中扩散系数,对比计算值与参考值,根据两者的差异,对液体热导率和粘度的经验公式进行修正,使其估算精度进一步提高。(2)构建多组分燃料乙醇柴油单液滴蒸发模型,开展燃料特性对蒸发过程的影响分析。液滴蒸发是缸内燃油雾化蒸发重要阶段,而乙醇柴油是由理化性质存在较大的组分构成,与柴油单液滴蒸发存在明显差异。根据缸内高温高压强旋流环境、高压喷射雾化液滴直径以及乙醇柴油理化性质的特点,提出应用曲线蒸馏模型同时耦合沸腾蒸发模型描述乙醇柴油单液滴蒸发时传质传热过程,借助文献验证模型的可行性。结合柴油机边界条件,获得燃料特性对液滴蒸发时传质传热过程的影响规律。(3)采用具有很强的工程应用前景的火焰面模型计算柴油机湍流扩散燃烧速率。针对乙醇柴油多组分燃料的特点,增加控制方程,扩展火焰面模型基础方程,使其能计算乙醇柴油湍流扩散燃烧速率。(4)基于ICFD-CN,搭建多组分燃料乙醇柴油的雾化燃烧平台。①根据网格单元温度和压力,采用修正后的物性公式改进ICFD-CN软件中fuel、evap、colide、lawall、chem和chemeq等模块中物性值计算代码；②耦合构建的多组分燃料蒸发模型,编写蒸发代码,替代ICFD-CN原有evap蒸发模块,修改其它辅助计算雾化蒸发的子模块相关代码；③进一步耦合包含CO、CO2生成的两步动力学反应预混合燃烧模型以及构建的多组分燃料扩散燃烧模型,编写程序,改进chem、chemeq和rinput模块,从而构建多组分燃料乙醇柴油的雾化燃烧仿真平台。以YZ4102ZLQ柴油为对象,利用激光喷雾试验和台架试验验证喷雾形态、缸内压力以及NOx排放。结果表明,计算值与实验吻合良好,可进一步应用于乙醇柴油发动机雾化燃烧过程的数值研究。该平台的构建,解决了原ICFD-CN软件不能预测乙醇柴油多组分燃料雾化燃烧过程的局限,对于由理化性质差异较大组成的混合燃料的燃烧过程仿真,具有重要的参考价值。(5)分析乙醇柴油燃料特性对喷射和雾化过程的影响规律。测量柴油机燃用十四烷和N5E10时高压油管嘴泵端压力,分析并获得燃料特性对高压油管内燃油压力波特性的影响规律。仿真围绕乙醇柴油燃料特性对连续射流初次雾化、液滴二次雾化、二次雾化特征参数对液滴半径敏感性、缸内燃油蒸发速率、气相流场和喷雾演变的影响,得出燃用乙醇柴油时会增加燃油射流产生的平衡区涡团脉动,同时探明缸内N5E10燃油雾化效果优于十四烷的根本原因。(6)利用台架试验,开展乙醇柴油发动机的燃烧和排放特性对助溶剂感受性研究。获得燃用乙醇柴油／柴油时气缸压力、放热率、预混合和扩散燃烧持续期和热量分配、燃烧重心、常规排放以及颗粒物粒径分布特性等方面变化规律。与柴油相比,乙醇柴油预混合燃烧期缩短,预混合燃烧阶段放热量比例降低,扩散燃烧期缩短,燃烧重心更加向上止点靠近。乙醇柴油的NOx和不透光烟度降低,且N5E10效果更好。乙醇柴油的排放颗粒物分布向小粒径方向移动,助溶剂种类对乙醇柴油燃烧颗粒粒径分布有影响；与N5E10相比,B10E10燃烧颗粒小粒径的质量分数进一步增加。(7)利用构建的仿真平台,数值分析乙醇柴油燃料特性对燃烧过程的影响规律。获得燃料特性对燃油质量蒸发速率、混合气分布、燃料浓度场、温度场、滞燃期和滞燃期形成可燃混合气数量、燃料燃烧速率以及燃烧过程中关键组分浓度的影响规律。十四烷中掺醇,燃烧稳定性得到改善,温度分布更加均匀,局部高温区减小,高温区形状由狭长型过渡为块状分布。燃用十四烷和N5E10时滞燃期以及滞燃期内形成的可燃混合气数量与燃烧始点判断方式有关。与十四烷相比,着火时刻N5E10缸内燃料瞬时燃烧速率略降低,预混合阶段质量燃烧速率与负荷有关,扩散阶段燃料燃烧速率提高。更多还原

【Abstract】 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.更多还原