Experimental investigation of nozzle cavitating flow characteristics for diesel and biodiesel fuels

This study was performed to clarify criteria for cavitation inception and the relationship between flow conditions and cavitation flow patterns of diesel and biodiesel fuels. The goal was to analyze the effects of injection conditions and fuel properties on cavitating flow and disintegration phenomena of flow after fuel injection. To accomplish this goal, it was utilized a test nozzle with a cylindrical cross-sectional orifice and a flow visualization system composed of a fuel supply system and an image acquisition system. In order to analyze the rate of flow and injection pressure of the fuel, a flow rate meter and pressure gauge were installed at the entrance of the nozzle. A long distance microscope device equipped with a digital camera and a high resolution ICCD camera were used to acquire flow images of diesel and biodiesel, respectively. The effects of nozzle geometry on the cavitating flow were also investigated. Lastly, a detailed comparison of the nozzle cavitation characteristics of both fuel types was conducted under a variety of fuel injection parameters. The results of this analysis revealed that nozzle cavitation flow could be divided into four regimes: turbulent flow, beginning of cavitation, growth of cavitation, and hydraulic flip. The velocity coefficient of diesel fuel was greatly altered following an increase in flow rate, although for biodiesel, the variation of the velocity coefficient relative to the rate of flow was mostly constant. The cavitation number decreased gradually with an increase in the Reynolds number and Weber number, and the discharge coefficient was nearly equal to one, regardless of cavitation number. Lastly, it could not observe cavitation growth in the tapered nozzle despite an increase in fuel injection pressure.     

Visualization of periodic flows over a sunroof opening by using a phase-marked PIV measurement

Flows over cavity openings are known to be highly structured and periodic due to the strong sound pressures emitted by the cavities. This article is concerned with the measurement of flow fields over the sunroof opening of an SUV. Since the PIV system used in the present work is not capable of taking phase-locked velocity fields during the measurement stage, phase-marked PIV measurements are performed and the phase-locked velocity fields are retrieved during a post-processing stage. The new PIV measurement method is shown to yield fairly accurate results with a proper choice of a phase-bandwidth. By using the phase-marked PIV measurement method, the evolution of large-scale structures in shear flow over the sunroof opening as phase changes is revealed. The detached shear layer is shown to fluctuate and then form a discrete large vortex convecting and impinging on the rear roof edge of the SUV. The average convection velocity of the vortex is calculated to be 0.45 of the nominal free stream flow velocity. Flow fields are compared for four different cases of deflector protrusion and a case without a deflector. Installation of a deflector can significantly change the flow field. For a deflector that reduces the buffeting noise by more than 10 dB, it is shown that turbulent fluctuations are initiated by the deflector but do not grow in amplitude as they convect downstream. As the deflector protrusion is increased, the amount of flow under the deflector increases in general. The flow exiting from the channel formed by the deflector and an A-frame is shown to increase the thickness of the shear layer near the leading edge of the sunroof opening.     

Hybrid three-dimensional mesh generation from quad-dominant surface meshes

A hybrid mesh generation algorithm using a modified plastering method for three-dimensional objects with variable thickness is presented. The method starts with a quad-dominant surface mesh and generates layered elements with variable thickness by using adaptive offsetting, resulting in hex-tet dominant mesh generation. Hexahedral and prismatic meshes are generated by the inward offsetting of the initial boundary mesh. In order to generate a conforming mesh, pyramid elements are constructed on top of hexahedral elements, and tetrahedral elements are generated for the remaining domain by using an advancing front method. This method is applied to several different geometries, and the effectiveness of the proposed algorithm is demonstrated.     

Prediction of interior noise by excitation force of the powertrain based on hybrid transfer path analysis

In the early design stage of a vehicle, simulation of interior noise is useful for assessment and enhancement of the noise, vibration and harshness (NVH) performance. Traditional transfer path analysis (TPA) technology cannot simulate interior noise since it uses an experimental method. In order to solve this problem, hybrid TPA is employed in this paper. Hybrid TPA uses simulated excitation force as the input force, which excites the flexible body of a car at the mount points, while traditional TPA uses the measured force. This simulated force is obtained by numerical analysis of the finite element (FE) model of a powertrain. Interior noise is predicted by multiplying the simulated force by the vibro-acoustic transfer function (VATF) of the vehicle. The VATF is the acoustic response in the compartment of a car to the input force at the mount point of the powertrain in the flexible car body. The trend of the predicted interior noise based on the hybrid TPA corresponds very well to the measured interior noise, with some difference due to not only experimental error and simulation error, but also the effect of the airborne path.     

Experimental study of the physical and chemical characteristics of biodiesel blended fuel using ultrasonic energy irradiation

The purpose of this study is to understand the physical and chemical characteristics of biodiesel blended fuel reformed by ultrasonic energy irradiation. To do this, a mixture of commercial diesel fuel and biodiesel was compared and analyzed according to whether or not ultrasonic energy irradiation was performed and the duration of irradiation. The results of the experiments indicate that when ultrasonic energy irradiation was performed on biodiesel blended fuel, its viscosity decreased by 3–7%. In the case of BD20, when ultrasonic energy irradiation was performed, its Sauter mean diameter (SMD) dropped by 12% on average. As the irradiation duration increased, the volume ratio of olefins increased up to a maximum of 2.7%, and the higher heating value increased to a maximum of 5.8%. On the contrary, the ratio of aromatics decreased by a maximum of 2.7%, and BI decreased by a maximum of 7%.     

串列双圆柱尾迹流的数值分析

为避免流体流动引起共振,采用有限体积法,对串列双圆柱尾迹流进行了数值分析,探讨了斯特劳哈尔数(Strouhal数)随圆柱间距比和雷诺数变化的规律.研究表明:在不同流场形态下,斯特劳哈尔数随圆柱间距比的变化规律不同;斯特劳哈尔数随雷诺数的增大而增大,但增大幅度与流场形态有关.     

Probe vehicle lane identification for queue length estimation at intersections

Vehicles instrumented with Global Positioning Systems, also known as GPS probe vehicles, have become increasingly popular for collecting traffic flow data. Previous studies have explored the probe vehicle data for estimating speeds and travel time; however, there is very limited research on predicting queue dynamics from such data. In this research, a methodology was developed for identifying the lane position of the GPS-instrumented vehicles when they are standing in the queue at signalized intersections with multiple lanes, particularly in the case of unequal queue. Various supervised and unsupervised clustering methods were tested on data generated from a microsimulation model. Among the tested methods, the Optimal Bayes Rule that utilizes probability density functions estimated using bivariate statistical mixture models was found to be effective in identifying the lanes. The methodology for lane identification was tested for queue length estimation. This research confirms that the lane identification is an important step required prior to the queue length estimation. The accuracies of the models for lane identification and queue length estimation were evaluated at varying levels of demand and probe vehicle market penetrations. In general, as the market penetration increases, the accuracy improves as expected. The result shows that 40% market penetration rate is adequate to reach about 90% accuracy.     

Relationships between characteristics of motorcycles and hydrocarbon emissions in Taiwan: A note

Taiwan’s inspection and maintenance (I/M) programs identifies high-emission motorcycles but, although these help reduce air pollution, they have been criticized for being cost-ineffective. This study examines the relationship between characteristics of motorcycles and hydrocarbon emissions in the Central Air Quality Basin of Taiwan. It is shown that engine size and type, age and manufacturer of a motorcycle significantly affect HC emissions. Larger-size engines emit smaller amounts of HCs; whereas older motorcycles emitted greater amounts. In addition, two-stroke-engine machines produced significantly higher HC emission levels than four-strokes. Variations in HC emissions testing are a result of various I/M testing locations and efficiency may be improved by modifying these.     

平板表面裂纹开口位移与其深度关系的确定

无限大三维弹性体内超奇异积分方程的解析解表明,位移间断与裂纹深度具有简单的比例系数关系.文章利用有限元法,对带有表面半椭圆型裂纹的平板结构进行计算,得到表面裂纹开口位移和名义应变的比值△u/ε,与表面裂纹深度D,之间同样具有简单的比例系数关系.该比例系数相关于边界条件.据此,文中提出一种裂纹深度估算的方法,并给出实验验证.     

Design and optimisation of wheel–rail profiles for adhesion improvement

This paper describes a study for the optimisation of the wheel profile in the wheel–rail system to increase the overall level of adhesion available at the contact interface, in particular to investigate how the wheel and rail profile combination may be designed to ensure the improved delivery of tractive/braking forces even in poor contact conditions. The research focuses on the geometric combination of both wheel and rail profiles to establish how the contact interface may be optimised to increase the adhesion level, but also to investigate how the change in the property of the contact mechanics at the wheel–rail interface may also lead to changes in the vehicle dynamic behaviour.