Search Results

This study focuses on fluctuations in the aerodynamic load acting on a hatchback car model under steady-state conditions, which can lead to degeneration of vehicle motion performance due to excitation of vehicle vibrations. Large eddy simulations were first conducted on a vehicle model based on a production hatchback car with and without additional aerodynamic devices that had received good subjective assessments by drivers. The numerical results showed that the magnitudes of the lateral load fluctuations were larger without the devices at Strouhal numbers less than approximately 0.1, where surface pressure fluctuations indicated a negative correlation between the two sides of the rear end, which could give rise to yawing and rolling vibrations. Based on the numerical results, wind-tunnel tests were performed with a 28%-scale hatchback car model.

The backward flow of the hot burned gas surrounding a diesel flame was found to be one of the factors dominating the set-off length (also called the lift-off length), that is, the distance from a nozzle exit into which a diffusion flame cannot intrude. In the combustion chamber of an actual diesel engine, the entrainment of the surrounding gas into a spray jet from a multi-hole nozzle is restricted by the walls and adjacent spray jets, which induces the backward flow of the surrounding gas. A new momentum theory to calculate the backward flow velocity was established by extending Wakuri's momentum theory. Shadowgraph imaging in an optical engine successfully visualized the backward flow of the hot burned gas.

The interaction of fuel sprays and in-cylinder flow in direct-injection engines is expected to alter kinetic energy and integral length scales at least during some portions of the engine cycle. High-speed particle image velocimetry was implemented in an optical four-valve, pent-roof spark-ignition direct-injection single-cylinder engine to quantify this effect. Non-firing motored engine tests were performed at 1300 RPM with and without fuel injection. Two fuel injection timings were investigated: injection in early intake stroke represents quasi-homogenous engine condition; and injection in mid compression stroke mimics the stratified combustion strategy. Two-dimensional crank angle resolved velocity fields were measured to examine the kinetic energy and integral length scale through critical portions of the engine cycle. Reynolds decomposition was applied on the obtained engine flow fields to extract the fluctuations as an indicator for the turbulent flow.

This paper presents typical flow structures around a 60%-scale wind-tunnel model of a Formula One (F1) car, using planar particle image velocimetry (PIV). The customized PIV system is permanently installed in a wind tunnel to help aerodynamicists in the development loop. The PIV results enhance the understanding of the mean velocity field in the two-dimensional plane in some important areas of the car, such as the front-wheel wake and the underfloor flow. These real phenomena obtained in the wind tunnel also help maintain the accuracy of simulations using computational fluid dynamics (CFD) by allowing regular checking of the correlation with the real-world counterpart. This paper first surveys recent literature on unique flow structures around the rotating exposed wheel, mostly that on the isolated wheel, and then gives the background to F1 aerodynamics in the late 2000s.

With the goal of improving drivability, this research aimed to clarify the mechanism of vehicle longitudinal acceleration, focusing on tip-in acceleration. Conventional typical analysis methods include experimental modal and model-based analysis. However, since the former requires the measurement of impulses and other input forces while the vehicle is stopped, measurement under actual driving conditions is difficult. The latter requires characteristic values such as the stiffness and damping coefficients to be identified in advance, which cannot be achieved either easily or precisely. Therefore, this paper proposes a new experiment-based analysis method. This method enables the acquisition of engine torque and transmission torque/force by measuring only the acceleration values of some components under driving conditions.

The effects of an increasing boost pressure, a high EGR rate and a high injection pressure on exhaust emissions from an HSDI (High Speed Direct Injection) diesel engine were examined. The mechanisms were then investigated with both in-cylinder observations and 3DCFD coupled with ϕT-map analysis. Under a high-load condition, increasing the charging efficiency combined with a high injection pressure and a high EGR rate is an effective way to reduce NOx and soot simultaneously, which realized an ultra low NOx of 16ppm at 1.7MPa of IMEP (Indicated Mean Effective Pressure). The flame temperature with low NOx and low soot emissions is decreased by 260K from that with conventional emissions. Also, the distribution of the fuel-air mixture plot on a ϕT-map is moved away from the NOx and soot formation peninsula, compared to the conventional emissions case.

Closed-form stress intensity factor solutions at the critical locations of spot welds in four types of commonly used specimens are obtained based on elasticity theories and fracture mechanics. The loading conditions for spot welds in the central parts of four types of specimens are first examined. The resultant loads on the weld nugget and the self-balanced resultant loads on the lateral surface of the central parts of the specimens are then decomposed into various types of symmetric and anti-symmetric parts. Closed-form structural stress and stress intensity factor solutions for spot welds under various types of loading conditions are then adopted from a recent work of Lin and Pan to derive new closed-form stress intensity factor solutions at the critical locations of spot welds in the four types of specimens.

A new clean diesel combustion concept has been proposed and its excellent performance with respect to gas emissions and fuel economy were demonstrated using a single cylinder diesel engine. It features the following three items: (1) low-penetrating and highly dispersed spray using a specially designed injector with very small and numerous orifices, (2) a lower compression ratio, and (3) drastically restricted in-cylinder flow by means of very low swirl ports and a lip-less shallow dish type piston cavity. Item (1) creates a more homogeneous air-fuel mixture with early fuel injection timings, while preventing wall wetting, i.e., impingement of the spray onto the wall. In other words, this spray is suitable for premixed charge compression ignition (PCCI) operation, and can decrease both nitrogen oxides (NOx) and soot considerably when the utilization range of PCCI is maximized.

In diesel engines with a straight intake port and a lipless cavity to restrict in-cylinder flow, an injector with numerous small-diameter orifices with a narrow angle can be used to create a highly homogeneous air-fuel mixture that, during PCCI combustion, dramatically reduces the NOX and soot without the addition of expensive new devices. To further improve this new combustion concept, this research focused on cooling losses, which are generally thought to account for 16 to 35% of the total energy of the fuel, and approaches to reducing fuel consumption were explored. First, to clarify the proportions of convective heat transfer and radiation in the cooling losses, a Rapid Compression Machine (RCM) was used to measure the local heat flux and radiation to the combustion chamber wall. The results showed that though larger amounts of injected fuel increased the proportion of heat losses from radiation, the primary factor in cooling losses is convective heat transfer.

This paper proposes a novel method of verifying comprehensive driver model used for the evaluation of driving safety systems, which is achieved by coupling the traffic simulation and the driving simulator (DS). The method consists of three-step procedure. In the first step, an actual driver operates a DS vehicle in the traffic flow controlled by the traffic simulation. Then in the next step, the actual driver is replaced by a driver model and the surrounding vehicle maneuvers are replayed using the recorded data from the first step. Then, the maneuver by the driver model is compared directly with the actual driver's maneuver along the simulation time steps.

Dynamic wind-tunnel tests of a simplified passenger car model were conducted using a two-degree-of-freedom model shaker. Time-resolved aerodynamic loads were derived from a built-in six-component balance and other sensors while the model underwent sinusoidal heaving and pitching motions at frequencies up to 8 Hz. The experimental results showed that frequency-dependent gains and phase differences between the model height/angle and the aerodynamic loads are in close agreement with those predicted by large-eddy simulation (LES) using an arbitrary Lagrangian-Eulerian (ALE) method. Based on these findings, transient aerodynamic loads associated with lateral motions were also estimated by LES analysis. Based on the above results, a full-unsteady aerodynamic load model was then derived in the form of a linear transfer function. The force and moment fluctuations associated with the vertical and lateral motions are well described by the full-unsteady aerodynamic load model.

A method of real time oil concentration measurment has been developed utilizing the effect of ultraviolet light absorption by lubricating oil in the liquid refrigerant line of an automotive air conditioning system. The light wavelengths from 200nm to 370nm are selected based on the ultraviolet light absorption sensitivity of the oils and refrigerants (CFC12,HFC134a). The effects of temperature,pressure and contaminantion on the absorbance of light are investigated in order to determine how these parameters affect the concentration measurement. The density changes of refrigerants are then compensated in the calculation for the oil concentration. The uncertainties of the overall concentration measurement are less than ±0.1 weight percent at 1 weight percent concentration. A transient oil circulation of the automotive air conditioner is measured by using this method.

Over the last few decades, in-cylinder visualization using optically accessible engines has been an important tool in the detailed analysis of the in-cylinder phenomena of internal combustion engines. However, most current optically accessible engines are recognized as being limited in terms of their speed and load, because of the fragility of certain components such as the elongated pistons and transparent windows. To overcome these speed and load limits, we developed a new generation of optically accessible engines which extends the operating range up to speeds of 6000 rpm for the SI engine version, and up to in-cylinder pressures of 20 MPa for the CI engine version. The main reason for the speed limitation is the vibration caused by the inertia force arising from the heavy elongated piston, which increases with the square of the engine speed.

The hole diameter of injection nozzles in diesel engines has become smaller and the nozzle coking could potentially cause injection characteristics and emissions to deteriorate. In this research, engine tests with zinc-added fuels, deposit analyses, laboratory tests and numerical calculations were carried out to clarify the deposit formation mechanisms. In the initial phase of deposit formation, lower zinc carboxylate formed close to the nozzle hole outlet by reactions between zinc in the fuel and lower carboxylic acid in the combustion gas. In the subsequent growth phase, the main component changed to zinc carbonate close to nozzle hole inlet by reactions with CO₂ in the combustion gas. Metal components and combustion gases are essential elements in the composition of these deposits. One way of removing these deposits is to utilize cavitations inside the nozzle holes.

In the case of engine bearings, pressure in a cylinder is necessary for the analysis of lubrication. In this study, a cycle simulation of gasoline engines has been developed to predict the pressure in the cylinder under the wide range of engine operation. In the cycle simulation, intake and exhaust processes are included and combustion process is calculated with flame propagation based on burning velocity. Here, the equation of ignition delay and the equation of burning velocity were determined with experimental results of a gasoline engine over wide A/F ratio. The pressure in the cylinder over the engine cycle is introduced into an elastohydrodynamic lubrication analysis of a con-rod bearing to calculate the load on the bearing in addition to the inertia force. Orbital movement, minimum film thickness, and power loss in the bearing were estimated over the wide range of engine operation.

When performing vibration analysis of complex vehicle structures, it is often important to be able to evaluate the effects of design changes in one or more substructures (e.g., for design optimization). It may also be convenient to allow different components to be modeled independently by different groups or organizations. For both cases, it is inevitable that some substructures will have non-matching finite element meshes at the interface where they are physically connected. Thus, a key challenge is to be able to handle the dynamic assembly of components with non-matching meshes and the subsequent global vibration analysis in a systematic and efficient manner. To tackle this problem, the enhancement of component mode synthesis methods for handling finite element models partitioned into non-matching substructures is considered in this paper. Some existing methods are reviewed, and new methods are developed.

Near-term energy policy for ground transportation is likely to have a strong focus on both gains in efficiency as well as the use of alternate fuels; as both can reduce crude oil dependence and carbon loading on the environment. Stratified-charge spark-ignition direct-injection (SIDI) engines are capable of achieving significant gains in efficiency. In addition, these engines are likely to be run on alternative fuels. Specifically, lower alcohols such as ethanol and iso-butanol, which can be produced from renewable sources. SIDI engines, particularly the spray-guided variant, tend to be very sensitive to mixture preparation since fuel injection and ignition occur within a short time of each other. This close spacing is necessary to form a flammable mixture near the spark plug while maintaining an overall lean state in the combustion chamber. As a result, the physical properties of the fuel have a large effect on this process.

Direct injection of natural gas under high pressure conditions has emerged as a promising option for improving engine fuel economy and emissions. However, since the gaseous injection technology is new, limited experience exists as to the optimum configuration of the injection system and associated combustion chamber design. The present study uses KIVA-3 based, multidimensional modeling to improve the understanding and assist the optimization of the gaseous injection process. Compared to standard k-ε models, a Renormalization Group Theory (RNG) based k-ε model [1] has been found to be in better agreement with experiments in predicting gaseous penetration histories for both free and confined jet configurations. Hence, this validated RNG model is adopted here to perform computations in realistic engine geometries.

A study of diesel fuel as a lubricant for diesel engines was conducted with the aim of dramatically reducing engine friction and eliminating the need to change the lubricating oil. A prototype single-cylinder engine modified for diesel fuel lubrication was made, and it was confirmed that firing operation is possible. Piston friction during the firing operation was reduced by modifying the shape of the cylinder liner surface to improve the retention of the lubricating oil. The study produced valid findings concerning engine lubrication, not only with diesel fuel, but also with ultra-low viscosity oil.

In recent years, problems such as global warming, the depletion of natural resources, and air pollution caused by emissions are emerging on a global scale. These problems call for efforts directed toward the development of fuel-efficient engines and exhaust gas reduction measures. As a solution to these issues, performance improvements should be achieved on the oil that lubricates the sliding sections of engines. This report points to features required of future engine oil-such as contribution to fuel consumption, minimized adverse effects on the exhaust gas aftertreatment system, and improved reliability achieved by sludge reduction-and discusses the significance of these features. For engine oil to contribution of engine oil to lower fuel consumption, we examined the effects of reduced oil viscosity on friction using gasoline and diesel engines.