Fatigue analysis for a multi-lap spot welded joint of high strength steel using quasi static tensile-shear test

The welding quality of spot weldment is an important factor that significantly affects the strength, stiffness, safety, and other performance characteristics of vehicles. Therefore, quality control and fatigue life evaluation of spot weldment are necessary processes. This paper presents a method for determining the fatigue life of multi-lap spot weldment of a high strength steel sheet. In this method, the fatigue life is estimated using the lethargy coefficient, which is the total defect coefficient according to rupture stress and time obtained by the quasi static tensile-shear test. The DC potential drop method was used to check initiation and propagation of cracks in addition to the test. Also, in this study, we modified the lethargy coefficient by using the welding current. Furthermore, we define a specific lapping constant, which is a characteristic constant of 2 or 3 lap weldments. The fatigue life obtained by the fatigue estimate equation, which contains a specific lapping constant was compared and verified with an experimental value. Finally we analyzed the relation of lap number, welding current and fatigue life. This method can save processing time and cost for predicting the life cycle of a structure.     

Effects of the fuel injection ratio on the emission and combustion performances of the partially premixed charge compression ignition combustion engine applied with the split injection method

Currently, due to the severity of world-wide air pollution by substances emitted from vehicles, emission control is being enforced more strictly, and it is expected that the regulation requirements for emission will become even more severe. A new concept combustion technology that can reduce the Nitrogen oxides (NOx) and PM in relation to combustion is urgently required. As a core combustion technology among new combustion technologies for the next generation engine, the homogenous charge compression ignition (HCCI) is expanding its application range by adopting a multiple combustion mode, a catalyst, direct fuel injection and partially premixed charge compression ignition combustion using the split injection method. This paper used a split injection method in order to apply the partially premixed charge compression ignition combustion method without significantly altering engine specifications of the multiple combustion mode and practicality by referring to the results of studies on the HCCI engine. Furthermore, the effects of the ratio of the fuel injection amount on split injection are investigated. From the test results, the adequate combination of the ratio of the fuel injection amount for the split injection method has some benefit on exhaust and fuel economy performance in a naturally aspirated single cylinder diesel engine.     

Development of the brake system design program for a vehicle

It is quite challenging to estimate the braking performance of a vehicle because the brake system is comprised of many parts, including a booster, master cylinder, and caliper. Calculation of characteristics such as braking force through vehicle tests requires much time and money. Therefore, the development of a method to estimate the braking performance of a vehicle using qualitative methods is beneficial. In this study, a program that can analyze the braking capabilities of a vehicle such as pressure, efficiency, and pedal travel is presented. The increase in disc temperature during braking as well as the properties of various boosters can be calculated using the proposed program. Dynamic characteristics of a vehicle equipped with a Load Sensing Proportional Valve (LSPV) were computed more precisely by obtaining the change in valve pressure according to the displacement of a suspension system. Since all input and output files are composed in the Microsoft Excel format, both design data management and database construction can easily completed.     

Experimental investigation of abrasive flow machining effects on injector nozzle geometries,engine performance,and emissions in a di diesel engine

The effects of the Abrasive Flow Machining (AFM) process on a direct injection (DI) Diesel engine fuel injector nozzle are studied. Geometry characterization techniques were developed to measure the microscopic variations inside the nozzle before and after the process. This paper also provides empirically-based correlations of the nozzle geometry changes due to the AFM process. The resulting impact of the process on the engine performance and emissions are also assessed with a DI Diesel engine test setup. This study shows that properly AFM-processed injectors can enhance engine performance and improve emissions due to the improved quality of the nozzle characteristics. However, an extended process can also cause enlargement of the nozzle hole as a side effect, which can adversely affect emissions. Emission measurements show the trade-off for the minimum levels as the process proceeds. Since the enlargement of the hole during the AFM process is not avoidable and must be minimized, strict control over the process is required. This control can be enforced by either limiting the AFM processing period, or by properly preparing the initial hole diameter so as to accommodate the inevitable changes in the nozzle geometry.     

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.     

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.