【作者】 张斌；

【导师】 白书战；

【作者基本信息】 山东大学 ， 车辆工程（专业学位）， 2021， 硕士

【摘要】 随着工业的发展和健康意识的增强,环境污染问题成为了现代人类的日常关注点,其中,人们对大气污染尤为关注,而大气污染以PM、氮氧化物和臭氧为主。柴油发动机因扭矩大、经济性能好被广泛应用于中大型载重车辆和工程机械,但柴油机带来的氮氧化物污染加重的问题,成为降低污染物研究的重点。当前高校和科研院所的研究人员以及发动机和后处理系统厂家的工程技术人员对于NOx后处理技术系统的理论研究和试验探索,取得了极大的进展。其中我国广泛采用的是SCR(选择性催化还原)技术,但对于SCR系统低温状态下引起的尿素热管理问题研究较少,因此本文对SCR尿素系统、冷却液以及不同尿素加热系统的解冻特性进行了试验研究,试验了在不同工况下尿素箱内尿素的解冻速率,对SCR系统在高原和高纬度地区的寒冷季节正常使用有很重要意义。首先分析了 SCR尿素系统各加热方式的优缺点和使用场景,电加热方式适合解冻所需热量不高的尿素供给系统,尿素箱内的尿素容量较多,采用电加热普通车辆的蓄电池难以持续供电,发动机冷却液加热尿素箱更适合,确定了适合实验室使用并贴近实车的加热方式。然后设计解冻试验方案,确定尿素溶解速率的测量逻辑。其次根据测量SCR系统尿素箱内尿素低温解冻速率的目的,首先分析了试验台架需要满足的需求,然后设计了模拟发动机冷却液加热系统的加热方式,建立了尿素测量系统热损失数学模型,尿素箱内换热数学模型,冷却液管路热损失数学模型,估算了热源的加热功率。为了实现模拟发动机冷却液对尿素的加热,设计了冷却液加热与循环系统,还设计了溶解尿素量测量系统、环境因素监测系统、振动模拟系统、尿素供给组件解冻系统。为了降低试验台的操作难度,利用Lab View软件编写了试验台操作界面。最后简单介绍试验台的集成与各部分功能的实现,通过模拟不同环境温度下的尿素系统的解冻并测量其解冻速率,发现增加冷却液流量能加速尿素箱内尿素的解冻,但随着环境温度的降低,其效果越来越小,需要发动机在该工况下提高转速,加快冷却液升温,才能更快的缩短尿素箱内尿素的解冻时间。更多还原

【Abstract】 With the development of industry and the enhancement of health awareness,environmental pollution has become a daily concern of modern humans.Among them,people are particularly concerned about air pollution,and air pollution is dominated by PM,nitrogen oxides and ozone.Diesel engines are widely used in medium and large heavy-duty vehicles and construction machinery due to their large torque and good economic performance.However,the problem of increased nitrogen oxide pollution caused by diesel engines has become the focus of research on reducing pollutants.At present,researchers from universities and scientific research institutes and engineers from engine and aftertreatment system manufacturers have made great progress in theoretical research and experimental exploration of NOx aftertreatment technology systems.Among them,SCR(Selective Catalytic Reduction)technology is widely used in my country,but there are few researches on urea thermal management problems caused by SCR system under low temperature.Therefore,this article analyzes the thawing characteristics of SCR urea system,coolant and different urea heating systems.The experimental study was conducted to test the thawing rate of urea in the urea tank under different working conditions,which is of great significance for the normal use of the SCR system in the cold season in plateau and high latitude regions.Firstly,the advantages and disadvantages and usage scenarios of the heating methods of the SCR urea system are analyzed.The electric heating method is suitable for the urea supply system that does not require high heat for thawing.The urea capacity in the urea tank is large,and it is difficult to continuously supply power by the battery of the electric heating ordinary vehicle.,The engine coolant heating urea tank is more suitable,and the heating method suitable for laboratory use and close to the actual vehicle is determined.Then design a thawing test program to determine the measurement logic of the urea dissolution rate.Secondly,according to the purpose of measuring the low-temperature thawing rate of urea in the urea tank of the SCR system,firstly,the requirements that the test bench need to meet are analyzed,and then the heating method that simulates the engine coolant heating system is designed,and the heat loss mathematical model of the urea measurement system is established.The mathematical model of heat transfer in the box and the mathematical model of heat loss in the coolant pipe estimate the heating power of the heat source.In order to simulate the heating of urea by engine coolant,a coolant heating and circulation system is designed,as well as a measurement system for the amount of dissolved urea,an environmental factor monitoring system,a vibration simulation system,and a thawing system for urea supply components.To reduce the difficulty of operating the test bench,the operation interface of the test bench was written using Lab View software.Finally,the integration of the test bench and the realization of each part of the function are briefly introduced.By simulating the thawing of the urea system under different ambient temperatures and measuring the thawing rate,it is found that increasing the coolant flow can accelerate the thawing of the urea in the urea tank,but with the ambient temperature The reduction of urea,its effect is getting smaller and smaller.It is necessary for the engine to increase the speed under this working condition and accelerate the heating of the coolant,in order to shorten the thawing time of the urea in the urea tank more quickly.更多还原