柴油机分流气体对冲排气消声单元气流速度分析研究

发布时间：2018-03-06 08:38

本文选题：柴油机　切入点：消声器　出处：《内蒙古农业大学》2017年博士论文　论文类型：学位论文

【摘要】：安装排气消声器是控制柴油机排气噪声的有效手段。传统柴油机的排气消声器由于其消声量与排气背压的矛盾导致其综合性能较差。因此,研发一种既消声性能好又排气背压低的新型消声器具有重要意义。研究发现,气流速度是一个决定消声器综合性能好坏的关键性因素。为此,课题组提出了一种分流气体对冲降速的消声原理,并基于该原理试制了消声单元。针对分流气体对冲消声单元,本文利用理论计算、数值模拟和试验分析的方法对其内部气流速度的变化规律进行了分析。首先设计了消声器试验系统,在此基础上,验证了气流速度对抗性消声器性能影响的重要性;分析了分流气体对冲消声单元气流对冲过程的速度变化规律以及对冲降速与内流场的关系;研究了消声单元结构参数对气流速度影响规律,并采用正交试验法确定了消声单元的较优结构参数组合;最后对分流气体对冲消声单元的性能进行了综合研究。得出以下主要结论:(1)建立了气流对冲过程气体微团纵向速度变化的数学模型。利用Matlab软件对气体微团在对冲过程中的速度变化进行了分析,结果显示,两股气流以一定速度对冲后,在对冲面附近纵向速度迅速降低到零。(2)对消声单元气流对冲过程的速度变化规律进行了分析。结果发现,两股气流对冲后,主流由纵向流动转变为横向流动,同时在对冲面附近形成了几处速度较低的涡流,整体速度大小得到了一定的衰减;在对冲区域中心处,纵向气流速度降到了最低,平均降幅为65%。在两个对冲区域连线的中间位置,横向气流受到二次对冲的作用,速度几乎降到了零。(3)对气流对冲与压力场的关系进行了试验研究。试验表明,两股气流对冲造成了一定的压力损失,占整个消声单元压力损失的50%左右,对冲过程中流体的平均阻力系数为0.91。(4)采用正交试验法分析了消声单元四种结构参数(内腔直径、对冲孔形状、对冲孔中心距、尾管过渡圆弧)对平均气流速度的影响规律,得到了其对消声单元气流速度的影响主次顺序,从主到次依次为内腔直径、对冲孔形状、尾管过渡圆弧半径、对冲孔中心距。(5)对分流气体对冲消声单元的性能进行了综合研究,并与CG25型单缸柴油机原装排气消声器进行了对比。结果显示,在中低频段分流气体对冲消声单元的平均传递损失提高了 30.8%,平均插入损失提高了 30%;当入口速度为30m/s时,分流气体对冲消声单元的压力损失降低了 16.8%;在相同入口速度条件下,分流气体对冲消声单元的湍动能分布范围小于原装消声器,而二者的湍动能最大值基本相等,在一定程度上反映了分流气体对冲消声单元的再生噪声小于原装消声器。
[Abstract]:The installation of exhaust muffler is an effective means to control the exhaust noise of diesel engine. The comprehensive performance of the exhaust muffler of traditional diesel engine is poor due to the contradiction between its muffling quantity and exhaust back pressure. It is of great significance to develop a new type of muffler with good muffler performance and low exhaust pressure. It is found that airflow velocity is a key factor to determine the overall performance of muffler. In this paper, we put forward a kind of sound suppression principle of shunt gas hedging and reducing speed, and based on this principle, we have trial-produced the silencing unit. In this paper, we use theoretical calculation to counter the noise reduction unit of shunt gas. Numerical simulation and experimental analysis are used to analyze the variation of the internal airflow velocity. Firstly, the muffler test system is designed, and the importance of the influence of the airflow velocity on the performance of the resistant muffler is verified. In this paper, the law of velocity variation and the relationship between the velocity reduction and the flow field in the process of the gas flow hedging are analyzed, and the influence of the structural parameters of the silencing unit on the velocity of the airflow is studied. The optimum structural parameter combination of the noise attenuation unit is determined by orthogonal test. The main conclusions are as follows: 1) the mathematical model of longitudinal velocity variation of gas microclusters in the process of gas flow hedging is established. The variation of velocity during punching is analyzed. The results show that the longitudinal velocity of the two streams is reduced rapidly to zero near the hedge surface after the two streams are hedged at a certain speed.) the law of the velocity variation of the silencing unit is analyzed. The results show that after the two air currents are hedged, the velocity changes are analyzed. The main stream changes from longitudinal flow to transverse flow, and at the same time, several low velocity eddies are formed near the hedge surface, and the overall velocity decreases to a certain extent, while at the center of the hedge area, the longitudinal flow velocity decreases to the lowest. In the middle of the line between the two hedges, the transverse flow is subjected to a secondary hedge, and the velocity drops to almost zero. 3) the relationship between the flow hedging and the pressure field is studied experimentally. The pressure loss is about 50% of the pressure loss of the whole silencing unit. The average resistance coefficient of the fluid in the hedging process is 0.91.4.The four structural parameters (the diameter of the inner cavity) of the silencing unit are analyzed by orthogonal test. For the shape of punching hole, the center distance of punching hole and the transition arc of tail tube), the influence law of the average airflow velocity is obtained, and the primary and secondary order of the influence on the airflow velocity of the silencing unit is obtained. The order from the main to the secondary is the diameter of the inner cavity, and the shape of the punching hole. In this paper, a comprehensive study on the performance of the shunt gas counteracting unit is carried out with the radius of the tailpipe transition arc and the center distance of the punching hole. The performance of the unit is compared with the original exhaust muffler of the CG25 type single-cylinder diesel engine. The results show that, The average transmission loss and average insertion loss of the counteracting unit in the low and medium frequency range are increased by 30.8 and 30, respectively; when the inlet velocity is 30 m / s, the average insertion loss is increased by 30 m / s. Under the same inlet velocity, the distribution range of turbulent kinetic energy of the shunt gas hedge silencing unit is smaller than that of the original muffler, and the maximum turbulent kinetic energy of the two units is basically equal. To some extent, it reflects that the regenerative noise of the shunt gas counteracting unit is less than that of the original muffler.
【学位授予单位】：内蒙古农业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：S218.5

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