Study on Transonic Tone in an Axisymmetric Supersonic Nozzle

This paper describes experimental and numerical works to investigate noise phenomenon in supersonic flow dis- charged from a convergent-divergent nozzle. The noise phenomenon of flow is generated by an emission of ＇transonic tones＇. The results obtained show that the frequency of a transonic tone, that differs from the frequency of a screech tone due to the shock-cell structures in a jet and originates in the shock wave in the nozzle, increases in proportion to the nozzle pressure ratio. The high-order transonic tone has the directivity in the direction of the flow. As for the transonic tone＇s frequency, the separated zone was calculated by using a simple flow model con- sidering the propagating perturbation. The results of the model corresponded to the results of this experiment well.     

Numerical analysis of Chevron nozzle effects on performance of the supersonic ejector-diffuser system

The supersonic nozzle is the most important device of an ejector-diffuser system.The best operation condition and optimal structure of supersonic nozzle are hardly known due to the complicated turbulent mixing,compressibility effects and even flow unsteadiness which are generated around the nozzle extent.In the present study,the primary stream nozzle was redesigned using convergent nozzle to activate the shear actions between the primary and secondary streams,by means of longitudinal vortices generated between the Chevron lobes.Exactly same geometrical model of ejector-diffuser system was created to validate the results of experimental data.The operation characteristics of the ejector system were compared between Chevron nozzle and conventional convergent nozzle for the primary stream.A CFD method has been applied to simulate the supersonic flows and shock waves inside the ejector.It is observed that the flow structure and shock system were changed and primary numerical analysis results show that the Chevron nozzle achieve a positive effect on the supersonic ejector-diffuser system performance.The ejector with Chevron nozzle can entrain more secondary stream with less primary stream mass flow rate.     

Effect of plate position and size for self-induced flow oscillation of underexpanded supersonic jet impinging on perpendicular plate

When the underexpanded supersonic jet impinges on the obstacle, it is well known that the self-induced flow oscillation occurs at the specific condition of the pressure ratio in the flowfield, the position of an obstacle and so on. This oscillation is related with the noise problems of aeronautical and other industrial engineering so that the characteristic and the mechanism of self-induced flow oscillation have to be cleared to control the various noise problems. But, it seems that the characteristics of t...     

柴油机可变喷嘴增压器控制逻辑设计与参数标定

为了满足排放法规、提高发动机的效率和加快动态充气的响应,针对配置可变喷嘴涡轮增压器（VNT）的轻型卡车柴油机,设计了增压压力控制逻辑。控制器根据发动机转速和喷油量查询增压压力脉谱（MAP）,确定目标增压压力。采用开环预控制和闭环PID控制相结合的控制结构对增压压力进行控制,并通过排放试验标定了增压压力基本MAP、预控制MAP和PID参数因子MAP。发动机试验台上的实际控制试验结果表明,发动机实际的增压压力能够有效跟踪设定值,控制误差不超过8％。     

基于PIC单片机的变喷嘴涡轮增压器电控系统设计

开发了一种以PIC单片机为核心的柴油机可变喷嘴涡轮增压器电子控制系统，介绍了该系统的工作原理，电控系统的硬件结构，控制算法和软件设计，并用实验进行了验证。     

柴油机喷嘴喷雾响声产生机理的研究

通过对两个不同密封座面直径的喷嘴分别在手压式喷油器校验器上和喷油泵试验台上所做的对比试验进行分析后 ,解释了喷油器在手压式喷油器校验器上检验时发出响声产生的机理。通过数据的频谱分析发现 ,不同的供油系统参数可以使喷油器产生不同频率的响声     

车用发动机VVT系统双积分自调节PID控制的研究

针对车用发动机VVT系统工况变化复杂、非线性和滞后性等特点,设计了双积分的PID控制策略,同时加入了积分预控的功能,并对微分部分作了自调节处理。通过试验验证了本VVT控制策略的可行性与实用性。     

柴油-液化石油气双燃料发动机放热规律的研究

利用CB366燃烧分析仪测录了柴油—液化石油气双燃料发动机和原柴油机在不同工况下的示功图,进行了放热规律的计算和对比分析,得出了有关双燃料发动机燃烧特性的结论     

CA6102汽油／LPG双燃料发动机动力性能的研究

为了解决解放CA6102发动机改装双燃料后动力性下降的问题,作者对LPG供气系统,点火系统,进气系统和燃烧系统进行了改进和优化,在不影响发动机经济性和排放的情况下,以实现发动机燃用LPG理动力性能下降不超过5％的目的。     

双燃料发动机(天然气/柴油)性能与排放的研究

以4102型柴油机为基础机，开发天然气／柴油双燃料发动机，试验研究引燃油量、喷油提前角对发动机排放和经济性影响，以及双燃料发动机与原柴油机性能和排放的比较。     

基于喷孔布置及喷射参数协调控制的双直喷发动机燃烧及碳烟排放特性研究北大核心CSCD

通过建立三维计算流体力学(computational fluid dynamic,CFD)柴油/天然气双直喷模型耦合多组分混合物简化化学动力学机理及现象学碳烟模型,模拟研究了天然气射流中心轴线与水平方向夹角α、天然气喷射持续期(natural gas injection duration,NID)的协调作用对柴油微引高压直喷天然气发动机燃烧过程及碳烟生成、氧化过程的影响。结果表明:缩短NID可提高扩散火焰的传播速度,增加燃烧区域的化学反应速率,且最高燃烧压力、峰值放热率、最大压力升高率(maximum pressure rise rate,MPRR)、指示热效率(indicated thermal efficiency,ITE)升高;随NID缩短,A_(4)、C_(2)H_(2)消耗反应速率增加,OH生成峰值增加,碳烟生成降低而氧化增强。增大α促进了大尺度涡旋结构的生成,降低了进入挤气区域的燃料比例,同时利于ITE的改善;较短的NID下,增大α后最高燃烧压力、峰值放热率提升明显;α增大至20°可显著降低A_(4)、C_(2)H_(2)生成峰值,抑制碳烟成核及表面生长反应,降低碳烟生成。综合考虑最高燃烧压力、ITE、MPRR及碳烟排放,确定两个优化方案分别为:α=15°&NID=16.5°及α=20°&NID=21.5°。     

汽油车燃油蒸发排放控制装置的研究

本文介绍了一套燃油蒸发排放控制系统 (EECS) ,此系统主要包括炭罐、清洗阀、油气分离器、翻车阀等。试验结果表明BJ2 0 2 0汽车安装该系统后 ,燃油蒸发排放仅为 0 31克 测量循环 ,远远低于GB1 4761 3-93中对轻型汽车的限值 ,并且该系统对发动机的功率和经济性没有影响。     

车用柴油机瞬变工况排放测试方法与控制措施初探

介绍了车用柴油机瞬态工况排放问题的由来,初步探讨了我国现阶段瞬态循环排放的研究方法。随着排放法规日益严格,瞬态排放要求已提到议事日程,限于我国现阶段瞬态循环排放测试实施有困难,通过稳态排放试验和瞬态工作过程模拟相结合的方法来研究瞬态排放性能,在一定程度上可弥补直接进行瞬态测试的困难。文中还讨论了控制和降低车用柴油机瞬态工况排放的一些措施及其效果。     

氧传感器参考电平自适应空燃比闭环控制方法研究

为了解决开关式氧传感器空燃比闭环控制点的漂移问题，建立了开关式氧传感器闭环控制的数学模型，并分析了氧传感器信号参考电平对空燃比闭环控制的影响，据此，提出了氧传感器参考电平自适应空燃比闭环控制方法，在发动机上试验了氧传感器参考电平对空燃比的影响规律，并进行了氧传感器参考电平的优化试验，结果表明，氧传感器参考电平自适应控制方法可以有效避免空燃比闭控制点随发动机工况变化的漂移问题，有效地降低了汽油机的排放。