超燃发动机流场组分浓度的在线测量

为了正确评价超燃发动机试验状态,采用自发拉曼散射技术在线测量了超燃发动机流场的主要组分。基于发动机试验条件和发动机与光学诊断技术的接口,建立了用于发动机流场组分测量的自发拉曼散射实验系统;测量了多车次发动机试验过程中流场主要组分的拉曼光谱;最后,通过光谱计算获得了流场主要组分浓度信息并重点分析了来流氧气含量及其变化情况。实验显示:发动机试验中,部分车次试验补氧后的来流中氧气的最大含量达到了30%,最小含量为18%,说明发动机试验过程中,对补氧量的控制精确和稳定性还有待提高。结果表明:采用自发拉曼散射技术可以较好地完成来流主要组分浓度测量工作,测量结果可用于发动机试验数据的分析及来流补氧控制方式和控制精度的改进。     

Thermal flow analysis of vehicle engine cooling system

This paper deals with theoretical model developed for analyzing the heat transfer of automotive cooling systems. The model has a modular structure which links various cooling system submodels. From the model, heat transfer rate of automotive cooling systems can be predicted, providing useful information at the early stages of the design and development. The aim of the study is to develop a simulation program for automotive cooling system analysis and a performance analysis program for analyzing heat exchanger. Heat release rate from combustion gas to coolant through the cylinder wall in engine cylinder was analyzed by using an engine cycle simulation program. In this paper, details of each submodel are described together with the overall structure of the vehicle model.     

A study on in-cylinder flow field of a 125cc motorcycle engine at low engine speeds

The in-cylinder flow characteristics of a four-stroke, four-valve, pent-roof small engine of motorcycle at engine speeds from 2000 rpm to 4000 rpm were studied using computational fluid dynamics (CFD). The aim of this study was to investigate the in-cylinder flow characteristics of small engines, including tumble, swirl, turbulent kinetic energy (TKE), angular momentum, in-cylinder air mass, turbulent velocity, turbulent length scale, and air flow pattern (in both intake and compression strokes) under motoring conditions. The engine geometry was created using SolidWorks, then was exported and analyzed using CONVERGE, a commercial CFD method. Grid independence analysis was carried out for this small engine and the turbulence model was observed using the renormalized group (RNG) k-ɛ model. The pressure boundary conditions were used to define the fluid pressure at the intake and exhaust of the port. The results showed that the increase in the engine speed caused the swirl flow in the small engine to be irregularly shaped. The swirl flow had a tendency to be stable and almost constant in the beginning of the compression stroke and increased at the end of compression stroke. However, the increase of in engine speed had no significant effect on the increase in tumble ratio, especially during the intake stroke. There was an increase in tumble ratio due to the increase in engine speed at the end of compression stroke, but only a marginal increase. The increase in engine speed had no significant effect on the increase in angular momentum, TKE, or turbulent velocity from the early intake stroke until the middle of the intake stroke. However, the angular momentum increased due to the increase in engine speed from the middle of the intake stroke to the end of compression stroke, and the angular momentum achieved the biggest increase when the engine speed rose from 3000 to 4000 rpm by 10 % at the end of the intake stroke. The increase in engine speed caused an increase of TKE and turbulent velocity from the middle of intake stroke until the end of compression stroke. Moreover, the biggest increase of TKE and turbulent velocity occurred when the engine speed rose from 3000 to 4000 rpm at the middle of intake stroke around 50 % and 25 %, respectively. Turbulent length scales appeared to be insensitive to increasing engine speed, especially in the intake stroke until 490 °CA. From that point, the value of the turbulent length scale increased as engine speed increased. The biggest increase in the turbulent length scales occurred when the intake valve was almost closed (around 20 %) and the engine speed was within two specific ranges (2000 to 3000 rpm and 3000 to 4000 rpm). Regarding the effect of engine speed, there were no significant effects upon the accumulated air mass in the small engine. The increase in engine speed caused an increase of turbulence in the combustion chamber during the late stages of the compression stroke. The increase in turbulence enhanced the mixing of air and fuel and made the mixture more homogeneous. Moreover, the increase in turbulence directly increased the flame propagation speed. Further research is recommended using a new design with several types of intake ports as well as combinations of different intake ports and some type of piston face, so that changes in air flow characteristics in small engines can be analyzed. Finally, this study is expected to help decrease the number of experiments necessary to obtain optimized systems in small engines.

     

发动机进气歧管流场的数值分析

以某发动机进气歧管为研究对象建立三维模型,运用CFD前处理软件Gambit划分网格,建立进气歧管流场模型,在计算流体动力学软件Fluent中分析各缸进气均匀性,进气歧管的进气阻力,进气歧管的内部流场特性。结果清晰显示各歧管的近壁流速、内部流速、表面总压分布情况,并根据分析结果对进气歧管进行了结构优化,改进后的发动机进气歧管在各缸进口减小总压损失、进气阻力、管二流量等方面取得较明显的效果,管四流量得到提高,各进气管不均匀度得到优化。     

气门升程调节对发动机缸内流场的影响

发动机功率由进气量、气缸内的气流运动以及燃烧质量决定,可变升程也可以通过改善这几个方面来达到提高发动机性能的目的。所以主要研究了不同工况下的升程调节对发动机缸内流场的影响,通过采用Fluent建立进气道-气门-气缸三维瞬态CFD模型,对发动机转速为2 000 r/min时两种气门升程模式下的两种调节情况进行了速度场的模拟计算。最后对计算结果进行对比分析,得出了气门升程模式2优于气门升程模式1的结论。     

Effect of engine variables on the turbulent flow of a spark ignition engine

The turbulent flow in a spark ignition engine plays an important role in determining its combustion characteristics and thermal efficiency. In order to analyse the combustion process, the turbulent flow and its turbulence intensity must be studied. To study the turbulent flow as varying various factors in a combustion chamber of a spark ignition engine, the L-head with or without squish area are selected. The turbulent as varying flow on the piston speed, inlet flow velocity, and squish velocity are measured by using hot wire anemometer. To examine the characteristics of turbulent flow, the ensemble averaged mean velocity, turbulence intensity, turbulence intensity decrease ratio, production rate of turbulence intensity, production coefficient of turbulence intensity are analysied.     

Measurement of lubricant flow in a gasoline engine

A residence time of approximately 60 s for lubricant in the piston ring pack of a gasoline engine, running at 1500 rpm, 50% throttle, has been measured by adding a hydrocarbon marker to the oil in the sump and monitoring its build up in oil extracted from the top ring groove. Comparison of the rate of increase of oxidised products in the sump with the level of oxidation in the ring pack allows a rate of flow of oil entering the ring pack from the sump to be calculated as approximately 0.4 cm³ min⁻¹ cylinder⁻¹, with at least 88% returning to the sump and the remainder lost into the combustion chamber. The volume of oil in the ring pack was determined as approximately 0.4 cm³ cylinder⁻¹, approximately one quarter of the free volume available between the top of the oil control ring and the top piston ring.     

Analysis of engine temperature and energy flow in diesel engine using engine thermal management

Recently, precise analysis of energy flow in engines has become necessary to improve fuel economy. An integrated engine thermal management model, which is introduced in this paper, is suitable for that process. The model consists of six sub-models for thermal mass, coolant, lubricant, heat transfer, friction, and exhaust. The sub-models are coupled to each other and they exchange heat and signals. Combustion energy flow analysis and temperature estimation of the engine components and working fluids were simulated under various conditions. Simulation results were compared with experimental data and they showed good agreement. Then, a variable-speed water pump (VSWP) to control coolant flow was applied in place of a conventional water pump. Engine warm-up time decreased with proper coolant flow control, and fuel economy could be improved by 2.5%.     

Performance measurement analysis of various cone flow meters with various beta edge types and flow field parameters

The beta edge, as one part of the cone element in cone flow meters, has several types. Cone flow meters with different beta edges have different applications and measurement performance. The sharp angle, corner cut and arc are the most common forms of beta edges used in cone flow meters. Their structures are analyzed without changing other parameters. Through theoretical analysis of their hydromechanics, a conclusion can be drawn that the discharge coefficient linearity error and permanent pressure loss in cone flow meters can be predicted based on the consistency in the recirculation quantity and the dissipation function value. The research objects are cone flow meters with different beta edge forms whose inner tube diameter is 100 mm and whose β values are 0.45, 0.55 and 0.65. The cone wake flow field characteristics were obtained and analyzed using the CFD method. Different beta edges cause different changes to the recirculation quantity and the dissipation in the cone wake flow region. Based on the theoretical prediction, the corner cut beta edge has the best discharge coefficient linearity error and relatively small permanent pressure loss. The accuracy of this prediction was experimentally verified. The experimental results demonstrate that the sharp-angle beta edge achieves the best performance in mechanical processing consistency, while the arc beta edge is the worst.     

吸收光谱法冲压发动机隔离段来流质量的流量测量

为实现冲压发动机地面直连试验中来流质量流量的测量校核,研制了吸收光谱法测量系统并开展了台架验证试验。首先,介绍了基于隔离段温度、流速测量计算质量流量的原理,针对台架试验环境适应性、长期工作稳定性问题,介绍了测量系统和光机设计方案,然后介绍了波长标定、温度与流速反演关键算法。在Ma6.5,6.0kg/s流量状态两个独立车次台架试验吸收光谱法计算质量流量的最大偏差为5%,验证了所提出方法的可行性。该方法为吸气式发动机来流状态的精细测量提供了新的方案和技术手段,未来可望用于来流捕获的实时反馈控制。     

Utilization of flow field simulations for cathode design in electrochemical machining of aerospace engine blisk channels

Electrochemical machining (ECM) cathode flow field design is crucial to machining aerospace engine blisk channels. In order to reduce the cathode design cycle and cost in machining, 3D cathodes and flow field simulation model were developed to facilitate analysis the flow fields in reversed flow patterns. The electrolyte flow line was determined by the distributions of electrolyte pressure, the diameter of the back orifice, and the areas of the back orifices in locations A, B, and C. The simulation results were utilized to analyze the influence of the electrolyte flow line. To verify the accuracy of the simulation, the experiments were carried out. The simulation results were consistent with the experiment data. It indicates that electrolyte flow field simulation is an effective method to optimize cathode design. Utilizing this methodology can improve the ECM cathode design efficiency and reduce cathode revision time.     

测量耙对尾喷管内流流场性能参数的影响

由于测量技术及传感器技术的限制,现有气动试验获得压力值的手段均为设置测量耙,尽管该方法使用历史悠久、测量准确,但依然难以满足航空发动机性能评价对于测量精度的要求。利用CFD技术研究喷管带/不带测耙时内流性能参数C_(f9)和C_(fg9)的变化说明测量耙对流场性能的影响,结果如下:固定几何的测耙对流场测量参数、计算参数的影响随着压比的增大而减小,其中推力修正系数相对误差最大不超过3.0%;带测耙流场云图类似于圆柱扰流,其损失区域明显可见;通过内流流场计算推力系数时应该采用P_(s9)/P_(t9),因为此时喷管出口欠膨胀。     

惯性振动筛运动主参数设计

对传统分级振动筛的运动及平衡分析,指出其致命弱点。给出盒式惯性传动机构作为振动发生器代替传统的振动方式,对惯性传动分级振动筛的工作原理及其主要运动参数的设计进行了分析计算。     

喷嘴几何参数对射流流场性能影响的计算研究

在边界条件和初始条件相同的情况下,分别改变圆锥带圆柱出口型喷嘴的圆锥段收缩角、喷嘴出口圆柱段长径比、喷嘴出口直径,用Fluent软件对圆喷嘴射流的速度衰减特性进行数值模拟和分析.模拟发现:在圆锥段收缩角为13°左右、喷嘴出口圆柱段的长径比为3左右时,射流核心段上的速度最大;随着喷嘴出口直径的减小,射流核心段上的速度不断增大,射流的切割性能也越来越好.数值模拟结果与实验结果完全一致.     

The mathematical model and the way to choose elastic suspension parameters of a supersmall mechanical sensor of inertial information

The mathematical models for calculating and analyzing the frequency of self-excited oscillations of the distributed system “elastic suspension-sensitive element” for the supersmall micromechanical gyroscope have been generated and investigated. Algorithmic and software support are developed. Geometrical parameters of the elastic suspension, which secure the resonance tuning of the sensor, are selected automatically by determining the frequency of self-excited oscillations.     

某型发动机燃油流量调节规律研究

发动机良好的燃油流量调节规律是发动机稳定工作的保证,为了更好的改善某型发动机燃油调节规律,本研究通过对燃油流量通道的建立,并对燃油通道执行机构电磁活门和回油活门占空比的分析,来研究燃油流量的调节规律。通过研究得出,燃油系统回油活门输出的位移信号与回油活门占空比成线性的关系,此结论可作为进一步改善此型发动机燃油流量调节规律的研究基础。     

大涵道比涡扇发动机测量参数精度分配

在航空发动机性能试飞中,测量参数传感器型号及精度的选择对于试验结果有着重要的影响。通过对测量参数进行随机误差合成的计算方法和对输出结果参数进行随机误差计算的两种计算机能方法,对某大涵道比涡扇发动机稳态净推力进行误差分析,计算结果表明两种方法均可用于净推力的随机误差分析。基于该结论,在给定净推力精度要求情况下,以等影响原则对各测量参数进行误差分析,计算出该发动机在设计状态下的精度分配结果。虽然计算模型有一定的假设,但该结果可以作为论证测试方案以及改装时的参考,具有一定的工程实用性。     

Effect of engine control parameters on combustion and particle number emission characteristics from a SIDI engine fueled with gasoline-ethanol blends

Journal of Mechanical Science and Technology - In this study, the impact of engine control parameters on combustion behaviors and particle number emissions was investigated with a spark ignition...     

发动机悬置系统参数的优化设计

发动机悬置系统的动态特性对整车的行驶平顺性有一定的影响，通过调整发动机悬置系统的悬置结构参数，可降低汽车行驶时的振动响应，对发动机悬置系统优化设计进行了分析，并针对某车振动较大的问题，对其发动机悬置系统进行了动态计算与优化设计，通过改进设计，使原车的整车振动状况得到了改善。     

Sensitivity analysis for estimation of inertial parameters of multibody mechanical systems

As an important issue, we first address in this paper the problem of a regression matrix with non-homogeneous physical units in the parameter estimation of multibody systems. This matrix contains the most important information about the motion of the system. Attention must be paid to this before implementing any parameter estimation algorithm due to the unit inconsistency in matrix multiplication required in such algorithms. A procedure to treat this problem in a proper way will be proposed. An experiment on a six degrees of freedom (DOF) robotic device, whose reference link follows a desired trajectory, is performed. The data collected from the experiment are then used for sensitivity analysis of inertial parameters based on the unit-homogenized regression matrix of the system. In this way, we characterize the influence of each selected inertial parameter on the dynamics of the system using unit-consistent mathematical manipulations.