Investigation on the flow and heat transfer characteristics of diesel engine EGR coolers

An important goal in diesel engine research is the development of a means to reduce the emissions of nitrogen oxides (NOx). The use of a cooled exhaust gas recirculation (EGR) system is one of the most effective techniques currently available for reducing nitrogen oxides. Since PM (Particulate Matter) fouling reduces the efficiency of an EGR cooler, a tradeoff exists between the amount of NOx and PM emissions, especially at high engine loads. In the present study, we performed engine dynamometer experiments and numerical analyses to investigate how the internal shape of an EGR cooler affects the heat exchanger efficiency. Heat exchanger efficiencies were examined for plain and spiral EGR coolers. The temperature and pressure distributions inside these EGR coolers were obtained in three dimensions using the numerical package program FLUENT.     

Scavenging a sub-chamber type CNG fueled engine

The sub-chamber type gasoline engine was suggested to be a type of clean engine, but the presence of residual gas in the sub-chamber was a serious fault. In this experimental study, the CNG direct injection method was applied to scavenge residual gas from the sub-chamber. The CVC (constant volume chamber) is divided into the sub-chamber and main-chamber and used as the main experimental apparatus. Because each combustion chamber of the CVC has an injector, the injector can be used freely, at the same time or individually. Therefore, the scavenging efficiency can be improved by changing injection times for the sub-chamber. The experimental results demonstrated that when all the fuel was injected into the sub-chamber, the combustion duration was shortened by 30% compared to that of injection into the main-chamber. Although residual gas was observed in the CVC, when the frequency of injections into the sub-chamber increased, good combustion characteristics were obtained.     

Experimental investigation and comparison of nanoparticle emission characteristics in light-duty vehicles for two different fuels

In recent years, particle number emissions rather than particulate mass emissions in automotive engines have become the subject with controversial discussions. Recent results from studies of health effects imply that it is possible that particulate mass does not properly correlate with the variety of health effects attributed to engine exhaust. The concern is now focusing on nano-sized particles emitted from I. C. engines. In this study, particulate mass and particle number concentration emitted from light-duty vehicles were investigated for a better understanding of the characteristics of the engine PM from different types of fuels, such as gasoline and diesel fuel. Engine nano-particle mass and size distributions of four test vehicles were measured by a condensation particle counter system, which is recommended by the particle measurement program in Europe (PMP), at the end of a dilution tunnel along a NEDC test mode on a chassis dynamometer. We found that particle number concentrations of diesel passenger vehicles with DPF system are lower than gasoline passenger vehicles, but PM mass has some similar values. However, in diesel vehicles with DPF system, PM mass and particle number concentrations were greatly influenced by PM regeneration. Particle emissions in light-duty vehicles emitted about 90% at the ECE15 cycle in NEDC test mode, regardless of vehicle fuel type. Particle emissions at the early cold condition of engine were highly emitted in the test mode.     

Development of an active front steering (AFS) system with QFT control

This paper investigates an active front steering control strategy based on quantitative feedback theory (QFT). By incorporating feedback from a yaw rate sensor into the active steering system, the control system improves the dynamic response of the vehicle. The steering response of a vehicle generally depends upon uncertain quantities like mass, velocity, and road conditions. Thus, QFT is used to design a controller with robust performance. A multi-degree-of-freedom nonlinear model is co-simulated here by MATLAB Simulink and ADAMS/CAR. The performance of the control system is evaluated under various emergency maneuvers and road conditions. The result shows that the designed robust control system has good control performance and can efficiently improve handing qualities and stability characteristics.     

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.