Investigation of soot formation in Diesel-GTL fuel blends under quiescent conditions

In this study, a visual investigation of sprays and flames is performed, and soot formation in Diesel-GTL fuel blends is studied in a specially designed quiescent constant-volume chamber under various ambient gas temperatures and O₂ concentrations. Similar to the case of soot formation during diesel fuel combustion, the sooting zone during the mixing-controlled combustion of Diesel-GTL blends is located in the leading portion of the jet boundaries. Auto-ignition delay and soot concentration decrease with an increase of GTL content in the fuel blend. Soot also decreases with lower O₂ concentration, higher injection pressure, and lower ambient gas temperature. The lack of soot formation at lower O₂ concentrations and lower temperatures suggests that Diesel-GTL fuel blends can be successfully utilized in low-temperature diesel combustion technologies that are currently being developed. Furthermore, this mixing controlled combustion method with Diesel-GTL blends can be used to modulate various engine operation parameters, and therefore to simultaneously reduce the formation of soot and NOx within a wide range of diesel engine loads.     

Performance analysis according to the combination of energy storage system for fuel cell hybrid vehicle

The need for the unmanned ground combat vehicle (UGCV), which is used for the surveillance, reconnaissance and targeting during extremely dangerous condition on the battlefield, has steadily increased, and the transition from manned ground combat vehicles to unmanned ground combat vehicles is expected to reduce the loss of lives during battle. The UGCV needs many types of capabilities to achieve satisfactory performance. This paper focuses on the modeling and control of the power system of the UGCV, and proposes the fuel cell hybrid system (FCHS) for the power system of the UGCV. The fuel cell hybrid system has many advantages in stealth drive and the system efficiency. In addition, the FCHS is much quieter than the engine generator and generates much less heat. The benefits of the FCHS are advantageous for use in Army operations, which require ‘silent watch’ capability and the ability to operate without showing up on an enemy’s radar screen. The FCHS has a fuel cell and uses an energy storage system (ESS) as a power source. The ESS (e.g., batteries or ultracapacitors) helps the fuel cell supply power to the electric drive system and also recovers energy during deceleration. The ESS makes it possible to improve the efficiency and dynamic characteristic of the power system. In this paper, the FCHS is composed of different combinations of component models. The component sizes are chosen to satisfy performance requirements. In order to determine the power distribution between the fuel cell and the ESS, a power management strategy based on the required power and the SOC (state of charge) of the ESS is proposed. Batteries and ultracapacitor, components of the ESS, have different characteristics. Accordingly, varying the combination of ESS components can change the performance of the power system. The performance of the FCHS with respect to different combinations of ESS is analyzed using simulated results.     

Development of evolutionary cone type LSD for SUV/RV utilizing the axiomatic approach and the ultrasonic nano crystal surface modification technology

Surface topology, cone angle and the forces acting on the cone of the clutch type limited slip differential (LSD) are major design parameters for the bias ratio and the noise condition. Therefore much research has been dedicated to these developments but the results have been used to submit patents. A new cone type limited slip differential for sport utility vehicles and recreational vehicles, which has a very simple structure and easy compliance with the vehicle performance, has been developed by the axiomatic approach and the ultrasonic nano crystal surface modification (UNSM) technology. The design criteria and optimal value of the design parameters are determined by the axiomatic approach utilizing CAE tools. Test methodologies in a test rig and in a vehicle were also developed. Test results showed good performance of bias ratio and noise level but durability is still under testing. This study is an extension of F2006P266, FISITA 2006.     

Design of Integrated Chassis Control logics for AFS and ESP

The performance of most electronic chassis control systems in the past has been optimized individually. Recently, a great research effort has been dedicated to the integration of chassis control systems in an effort to improve the vehicle performance. This involves orchestration of individual control modules so that they can jointly contribute to the enhancement of their control effect. In this research, two integrated control logics for AFS (Active Front Steering) and ESP (Electronic Stability Program) have been developed. Of the two logics, one uses a supervisor that rules over the individual modules. The other logic uses a CL (Characteristic Locus) method, which is a frequency-domain multivariable control technique. The two logics have been tested under various driving conditions to investigate their control effects. The results indicate that the proposed integrated control logics can yield vehicle performance that is superior to that of the individual control modules without any integration scheme.     

Theoretical studies of active power/angle sub-matrix in power flow Jacobian for power system analysis

Properties of the active power/angle sub-matrix in the power flow Jacobian for power system analysis are studied. The sub-matrix is a dominant and irreducible matrix under very general conditions of power systems, so that it is invertible. Also the necessary conditions for its singularity are given. These theoretical results can be used to clarify the ambiguous understanding of the sub-matrix in current literature, and also provide the theoretical foundations for the applications based on reduced power flow Jacobian. Numerical simulation on the IEEE 118-bus power system is used to illustrate our results.     

Numerical experiments on an ill-posed inverse problem for a given velocity around a hydrofoil by iterative and noniterative regularizations

For a given velocity distribution around a hydrofoil, the inverse problem of the hydrofoil is studied. The inverse problem is formulated by representing the hydrofoil in terms of vortices within the framework of linear potential theory. From the mathematical formulation, it is known that the inverse problem turns out to be ill-posed in the usual topology. In this paper, iterative and noniterative regularizations are applied to solve the problem and to find their suitability for the two-dimensional inverse hydrofoil problem. Numerical experiments demonstrate that the regularization methods are accurate and suitable for the inverse mathematical formulation for a given velocity distribution around a hydrofoil. Received: June 6, 2000 / Accepted: December 8, 2000     

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.