Effects of stack array orientation on fuel cell efficiency for auxiliary power unit applications

The commercial fuel cell products currently appearing on the market are self-contained fuel cell engines. These engines can be used for many applications that are presently dominated by internal combustion engines or batteries. Vehicle mounted fuel cell auxiliary power units have been attracting attention lately. Additionally, there is a market based incentive to use multiple small fuel cell arrays in place of a single large fuel cell for some applications. Typically, fuel cells are designed to operate as stand-alone units. This paper investigates the ability of small commercial stacks to operate in common array arrangements. Although an individual Nexa is able to produce 1500 W, Dual Nexas do not maintain that capability while in array configurations. With an overall load share ratio of 1.02:1 the series array reliably produced 2900 W of power, while with an overall load share ratio of 1.09:1 the parallel array reliably produced only 2800 W of power. This study shows that array orientation affects both system stack net efficiency and individual stack net efficiency. The information gained from this study may be helpful for fuel cell design and integration.     

Numerical study of a light-duty diesel engine with a dual-loop EGR system under frequent engine operating conditions using the doe method

Exhaust gas recirculation (EGR) is an emission control technology that allows for a significant reduction in NOx emissions from light- and heavy-duty diesel engines. The primary effects of EGR are a lower flame temperature and a lower oxygen concentration of the working fluid in the combustion chamber. A high pressure loop (HPL) EGR is characterized by a fast response, especially at lower speeds, but is only applicable if the turbine upstream pressure is sufficiently higher than the boost pressure. On the contrary, for the low pressure loop (LPL) EGR, a positive differential pressure between the turbine outlet and the compressor inlet is generally available. However, a LPL EGR is characterized by a slow response, especially at low and moderate speeds. In this study, of the future types of EGR systems, the dual-loop EGR system (which has the combined features of the high-pressure loop EGR and the low-pressure loop EGR) was developed and was optimized under five selected operating conditions using a commercial engine simulation program (GT-POWER) and the DOE method. Finally, significant improvements in the engine exhaust emissions and performance were obtained by controlling several major variables.     

Design of active suspension and electronic stability program for rollover prevention

This paper presents a method for the design of a controller for rollover prevention using active suspension and an electronic stability program (ESP). Active suspension is designed with linear quadratic static output feedback control methodology to attenuate the effect of lateral acceleration on the roll angle and suspension stroke via control of the suspension stroke and tire deflection of the vehicle. However, this approach has a drawback in the loss of maneuverability because the active suspension for rollover prevention produces in vehicles an extreme over-steer characteristic. To overcome this drawback of the active suspension based method, ESP is designed. Through simulations, the proposed method is shown to be effective in preventing rollover.     

Processing and fiber content effects on the machinability of compression moulded random direction short GFRP composites

The random direction short Glass Fiber Reinforced Plastics (GFRP) have been prepared by two compression moulding processes, namely the Preform and Sheet Moulding Compound (SMC) processes. Cutting force analysis and surface characterization are conducted on the random direction short GFRPs with varying fiber contents (25∼40%). Edge trimming experiments are preformed using carbide inserts with varing the depth of cut and cutting speed. Machining characteristics of the Preform and SMC processed random direction short GFRPs are evaluated in terms of cutting forces, surface quality, and tool wear. It is found that composite primary processing and fiber contents are major contributing factors influencing the cutting force magnitudes and surface textures. The SMC composites show better surface finish over the Preform composites due to less delamination and fiber pullouts. Moreover, matrix damage and fiber protrusions at the machined edge are reduced by increasing fiber content in the random direction short GFRP composites.     

Development of an on-line model to predict the in-cylinder residual gas fraction by using the measured intake/exhaust and cylinder pressures

The in-cylinder RGF (residual gas fraction) of internal combustion engines for new combustion concepts, such as CAI (controlled auto ignition) or HCCI (homogenous charged compression ignition), is a major parameter that affects the combustion characteristics. Thus, measurement or prediction of the cycle-by-cycle RGF and investigation into the relation between the RGF and the combustion phenomena are critical issues. However, on-line prediction of the cycle-by-cycle RGF during engine testing is not always practical due to the requirement of expensive, fast response exhaust-gas analyzers and/or theoretical models that are just too slow for application. In this study, an on-line model that can predict the RGF of each engine cycle and cylinder during the experiment in the test cell has been developed. This enhanced model can predict the in-cylinder charge conditions of each engine cycle during the test in three seconds by using the measured dynamic pressures of the intake, exhaust, and cylinder as the boundary conditions. A Fortran77 code was generated to solve the 1-D MOC (method of characteristics). This code was linked to Labview DAQ as a form of DLL (dynamic link library) to obtain three boundary pressures for each cycle. The model was verified at various speeds and valve timings under the CAI mode by comparing the results with those of the commercial code, GT-Power.     

Analysis of neck fractures from frontal collisions at low speeds

Neck fracture is a major cause of death in traffic accidents. This pattern of injury normally occurs in a frontal collision or overturn of a vehicle. This study investigates the case of a neck fracture from a low-speed collision. In the examined case, the passenger in the front seat of the car fractured his neck and died. He did not have his seatbelt on when the vehicle slipped on a frozen road surface on a downward slope of a hill and impacted into the shoulder of the road at low speed. In this type of collision, an occupant’s body will be impacted by the windshield or other interior trim of the car. However, in this case, rather unusually, neither body tissue nor fiber remained although the collision involved a broken windshield. Thus, the reason for the passenger death was unidentified. This study applied the computer simulation package Madymo for analyzing the accident. The result of the simulation was that the passenger, who did not wear a seatbelt, moved forward due to inertia. The upper part of the passenger then rotated and lifted when the knee contacted with the dashboard. By evaluating the structural deformation of the vehicle at the front, we deduced that the collision velocity was 30 km/h. Through a computational experiment that was undertaken using Madymo 7.0, NIC was estimated to be 240 m²/s². This result far exceeded the threshold for neck injuries. In particular, in comparison with whiplash injuries, when the passenger’s head directly impacts the roof following a rear-end collision, the bending moment through hyperextension of the neck is greatly increased. In this study, we concluded that the manner of death was the hyperextension of the neck, as the passenger’s head contacted the roof from underneath.     

Low cost design of parallel parking assist system based on an ultrasonic sensor

This paper presents a low cost design and implementation of a parallel parking assist system (PPAS) based on ultrasonic sensors. Generally, a PPAS requires several types of sensors, such as an ultrasonic sensor, camera sensor, radar sensor and laser sensor for parking space detection. However, our proposed PPAS only requires two ultrasonic sensors on the front and lateral sides for parking space detection. Moreover, a steering angle sensor and wheel speed sensor installed in the vehicle are used to obtain vehicle position information for localization in ultrasonic range data. The hardware architecture of the PPAS based on an electronic control unit (ECU) module, sensor modules and a human machine interface (HMI) module was proposed. Moreover, the software architecture of the PPAS is based on system initialization, scheduling, recognition and a control algorithm. In particular, a novel sensor algorithm was proposed to minimize the vehicle corner error of the ultrasonic sensor. A prototype of the PPAS based on the proposed architecture was constructed. The experimental results demonstrate that the implemented prototype is robust and successfully performs parking space detection and automatic steering control. Finally, the low cost design and implementation of the PPAS was possible due to the cheap ultrasonic sensors, simple hardware design and low computational complexity of the proposed algorithm.     

Analysis of an automotive ground system based on its steady-state model

As more electrical equipment is installed and larger currents are required in vehicles, the automotive ground system becomes more important to guarantee the stable operation of the equipment and efficient power consumption. In this paper, an automotive ground system is analyzed in a steady-state condition, and a simulation model for estimating its ground voltage distribution is described. The automotive ground system is divided into an engine compartment ground and a body ground, and it is modeled as an equivalent resistor network, which is suitable for simulation. By using the developed model, ground voltages are simulated and measurements are taken with a real car. A comparison of the simulation and measurement results shows good agreement, and the validity of the model is confirmed. Then, the factors that dominate the ground voltage level are discussed.     

Estimation of the adhesion force for a disc brake in a skid control condition

The performance of brakes has become important due to increased train speeds. The brake system of a train must possess a large brake force to stop the train safely within a limited stopping distance. However, an excessive brake force deteriorates the ride comfort and causes the train to skid. Therefore, it is necessary to control the brake force within the adhesion force limit. This paper presents an analytical method to estimate the relationship between the brake and adhesion forces of a disc brake system. This method has been applied to the actual disc braking control system of the Korea High-Speed Train (HSR350x), and the adhesion force is estimated in an actual skid condition.     

Model-based control of an electropneumatic brake system for commercial vehicles

A properly functioning brake system is critical for ensuring the safe operation of any vehicle on roadways. Commercial vehicles such as trucks, tractors-trailers and buses are equipped with an air brake system that uses compressed air as the energy transmitting medium. This paper presents a model-based control scheme for an electropneumatic brake system for use in commercial vehicles. A mathematical model for an electropneumatic brake system was developed and corroborated with experimental data. A control scheme was developed based on this model and was used to regulate the pressure of air inside the brake chamber according to a desired pressure trajectory. This control scheme was implemented on an experimental test bench, and its performance was studied for various values of the controller parameter. The control scheme was tested for various desired pressure trajectories reflecting actual brake operation.