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A novel mechanical method of achieving a rapid switch between stoichiometric and lean conditions for SI engines is explored. Two and three throttle configurations, a switch strategy which employs a standard intake manifold and an assembly of pipes and throttle(s), are investigated numerically by using a one-dimensional engine simulation program based on the method of characteristics. The results indicate that it is possible to achieve rapid AFR switch without a torque jump, i.e. unperceptible to the driver.

To investigate the ignition process in a diesel spray, the ignition in a transient fuel spray is analyzed numerically by a simple quasi-steady spray model coupled with the Shell kinetics model at various operating conditions and validity of this model is assessed by a comparison with existing experimental data. The calculated results indicate that the competition between the heat absorption of fuel and the hot air entrainment determines the equivalence ratio of mixtures favorable for the ignition to occur in the shortest time.

The paper presents a computer simulation of flow and heat transfer phenomena in the intake port of a spark ignition engine with port fuel injection. Engine cold starting conditions are studied including the effects of in-cylinder mixture back flow into the port. One dimensional air flow and wall fuel film flow models and a two dimensional fuel droplet flow model have been developed using a combination of finite difference approaches. As a result, predictions are obtained that provide detailed picture of the air-fuel mixture properties along the intake port. The model may be of special importance for exhaust gas ignition system simulation as it will provide data concerning mixture formation under conditions of excessive fuel injection during engine start-up. The calculations performed are shown to be phenomenologically correct.

The purpose of this study is to investigate the turbulent mixing in a diesel spray by large eddy simulation (LES). As the first step for the numerical simulation of diesel spray by LES, the LES of transient circular gas jets and particle laden jets were conducted. The simulation of transient circular jets in cylindrical coordinates has numerical instability near the central axis. To reduce the instability of calculation, azimuthal velocity around the central axis is calculated by the linear interpolation and filter width around the axis is modified to the radial or axial grid scale level. A transient circular gas jet was calculated by the modified code and the computational results were compared with experimental results with a Reynolds number of about 13000. The computational results of mean velocity and turbulent intensity agreed with experimental results for z/D>10. Predicted tip penetration of the jet also agreed to experimental data.

This paper describes a heat transfer model currently being developed for a next generation controlled atmosphere brazing furnace for production of automotive aluminum heat exchangers. This furnace will be numerically controlled to improve product yield. Part of the control loop decision will be based on predicted heat exchanger temperatures for set operating conditions. The numerical program is a transient heat transfer model simulating the radiant heat transfer between the furnace and the heat exchanger and the conduction heat transfer within the heat exchanger. The program solves the three-dimensional conduction equation for a solid using an implicit finite difference method. The boundary conditions to the solid is the radiant heat exchange. The program determines the radiant heat exchange based on the assumption of gray diffuse surfaces.

Unsteady laminar flame propagation confined in a closed cylindrical combustion bomb is studied by numerical computation for an axisymmetric two-dimensional laminar flame. Computation includes complete two-dimensional unsteady Navier-Stokes equations of change for a chemically reacting propane-air mixture. Implicit Continuous fluid Eulerian, Arbitrary Lagrangian Eulerian finite difference technique, simplified reaction kinetics models, and artificial flame stretching transformation and inverse transformation were adopted in the calculation. Physically realistic flame behavior can be demonstrated even with rather coarse computing cell size, simplified reaction kinetics models, and personal computer level low power computing machines.

The aerodynamic characteristics of automobiles have received substantial interest recently. Detailed knowledge of vehicle aerodynamics is essential to improve fuel efficiency and enhance stability at high-speed cruising. In this study, a numerical simulation has been carried out for three-dimensional turbulent flows around a commercial bus body. Also, the effect of a rear-spoiler attached at the rear end of the bus body was investigated. The Navier-Stokes equation is solved with the SIMPLE method in a general curvilinear coordinates system. RNG k- ε turbulence model with the MARS scheme was used for evaluating aerodynamic forces, velocity and pressure distribution. The results show that complex wake structure in the immediate rear of the bus body has been confirmed. The rear-spoiler modifies the near wake structure and decreases aerodynamic drag and improvement in lift force was achieved.

The three equilibrium equations governing the large deflections of thin plates are presented. A finite-difference overrelaxation technique is developed for the approximate solution of this system of nonlinear partial differential equations on a digital computer. To insure stability and speed up convergence of the numerical solution, nonlinear terms in the equations are treated as constants, which are evaluated periodically as the iteration proceeds. This method gives stable solutions for practically all ranges of the over-relaxation factor; therefore, the overrelaxation factor can be chosen to give convergence in the minimum number of iterations. Results obtained by using this technique on a simple plate bending problem and the corresponding results obtained by Levy and Wang are presented for comparison.

With many advantages of GDI technology, one major disadvantage is high HC emissions. The primary goal of this study is to determine the optimum values of engine parameters that would result in maximum power output from a GDI engine, with complete combustion, minimum hydrocarbon (HC) emissions, and minimum specific fuel consumption. A two-dimensional engine geometry with a piston-bowl was selected for faster engine CFD simulations. The first part involves a study of the affect of engine parameters on performance and HC emissions. The parameters considered were, equivalence ratio (mass of injected fuel), injection timing, ignition timing, engine RPM, spray cone angle, and velocity of fuel injection. The second part of the study involves determining the optimum values of fuel mass injected, injection timing, and ignition timing in order to maximize power output while limiting the amount of fuel left unburned after the end of the expansion process.

In this paper, a novel 3-D dynamic/crash mathematical model is developed and solved numerically to investigate the influence of Vehicle Dynamics Control Systems (VDCS) on vehicle collision mitigation in offset crash scenarios. In this model, the VDCS are co-simulated with a four-wheel vehicle dynamic model and integrated with a nonlinear front-end structure model. In addition, the vehicle body is represented by a lumped mass and four spring/damper units are used to represent the vehicle suspension system. The numerical simulations demonstrate that the vehicle dynamic responses and influence of VDCS on vehicle collisions are captured and analyzed accurately. Furthermore, the mathematical model is shown to be flexible, useful and can be used in optimization studies. The model is validated by comparing the numerical results with other published results and good correlations are achieved.

Spray impingement is an important phenomenon that introduces turbulence into the spray that promotes fuel vaporization, air entrainment and flame propagation. However, liquid impingement on the surface leads to wall-wetting and film deposition. The film region is a fuel-rich zone and it has potentials to produce higher emission. Film deposition in a non-reacting spray was studied previously but not in a reacting spray. In the current study, the film deposition of a reacting diesel spray was studied through computational fluid dynamic (CFD) simulations under a variety of ambient temperatures, gas compositions and impinging distances. Characteristics of film mass, distribution of thickness, soot formation and temperature distributions were investigated. Simulation results showed that under the same impinging distance, higher ambient temperature reduced film mass but showed the same liquid film pattern.

Automotive refueling is gaining greater importance because fuel vapors released during refueling are believed to increase ozone levels in urban areas. As a step towards On-Board Refueling Vapor Recovery (ORVR) designs, vapor generation and transport during refueling needs to be understood to develop recovery techniques. The objective of the present study is to understand the fluid flow inside the automotive gas tank filler pipe using commercially available Computational Fluid Dynamics (CFD) software. This effort is expected to yield detailed flow field information, including air entrainment. The phenomena of well-back, the process of fuel flooding the filler pipe and flowing backwards at the filler pipe mouth, and the pressure transients inside the tank leading to premature nozzle shut-off were examined. The current work includes unsteady CFD simulation with gasoline and air as the working fluids.

The flow through diesel fuel injector nozzles is important because of the effects on the spray and the atomization process. Modeling this nozzle flow is complicated by the presence of cavitation inside the nozzles. This investigation uses a two-dimensional, two-phase, transient model of cavitating nozzle flow to observe the individual effects of several nozzle parameters. The injection pressure is varied, as well as several geometric parameters. Results are presented for a range of rounded inlets, from r/D of 1/40 to 1/4. Similarly, results for a range of L/D from 2 to 8 are presented. Finally, the angle of the corner is varied from 50° to 150°. An axisymmetric injector tip is also simulated in order to observe the effects of upstream geometry on the nozzle flow. The injector tip calculations show that the upstream geometry has a small influence on the nozzle flow. The results demonstrate the model's ability to predict cavitating nozzle flow in several different geometries.

A numerical study is presented for high-lift airfoils suitable for racecar applications. The study includes the effect of ground clearance (distance between the airfoil and the ground), angle of attack and Reynolds number based on airfoil chord length. The finite volume code CFL3D, developed by NASA Langley Research Center, is used in the study. Four airfoils are used to represent different airfoil families. The study shows that Reynolds number has a very small effect on the downforce and the drag. Medium and large ground clearance are studied. For medium ground clearance the downforce and the drag increase, as airfoil gets closer to the ground. A considerable increase in the downforce can be gained by even small changes in the ground clearance. As the angle of attack increases both the drag and the downforce increase as expected. For large ground clearance the airfoil performance is close to the freestream case.

The pulsating flow in a duct with a junction was studied numerically using a Random-Choice Method and the experiments were carried out to check if this numerical simulation is valid or not. As a result, good agreement was found between the experiment and numerical calculation. Concerning the location of the shock wave the agreement was excellent. The Random-Choice Method may be applied to real reciprocating engines by coupling it to a multi-dimensional in-cylinder simulation.

A numerical scheme known as the Random-Choice Method was applied to analyze the pulsating flow in a pipe with and without a nozzle. Good quantative agreement between shock locations obtained experimentally and numerically was found. Furthermore, the pressure histories of flow upstream of the nozzle show good quantitative agreement.

Radiator thermal cycle test is a test method to check out the robustness of a radiator. During the test, the radiator is going through transient cycles that include high and low temperature spikes. These spikes could lead to component failure and transient temperature map is the key to predict high thermal strain and failure locations. In this investigation, an accurate and efficient way of building a numerical model to simulate the transient thermal performance of the radiator is introduced. A good correlation with physical test result is observed on temperature values at various locations.

A numerical study on sunroof noise reduction is carried out. One of the strategies to suppress the noise is to break down the strong vortices impinging upon the trailing edge of the sunroof into smaller eddies. In the current study, a serrated sunroof trailing edge with sinusoidal profiles of wavelengths is investigated for the buffeting noise reduction. A number of combinations of wavelengths and amplitudes of sinusoidal profiles is employed to examine the effects of trailing edge serrations on the noise reduction. A generic vehicle model is used in the study and a straight trailing edge is considered as a baseline. The results indicate that the trailing edge serration has a significant impact on the sound pressure level (SPL) in the vehicle cabin and it can reduce the SPL by up to 10~15 dB for the buffeting frequency.

Over the past years, the so-called Flame Speed Closure (FSC) model was shown to be a very promising tool for multi-dimensional simulations of premixed turbulent combustion in internal combustion and gas turbine engines. The laboratory tests and industrial applications of the model have been mainly limited to moderately turbulent flames. In the paper, three alternative versions of the FSC model, which yield different results at weak turbulence but similar results at moderate one, are discussed and numerically tested against recent experimental data reported by the Leeds [27,34] and Rouen [28] groups for expanding, statistically spherical, premixed, weakly turbulent flames. The computed and measured data on the mean combustion progress variable profiles, mean flame brush thickness development, and observed flame speeds are compared in order to assess and rank the submodels discussed.

A numerical analysis method is developed for predicting the pressure fluctuations on the front side window surface, aiming at the elucidation of the external aerodynamic flow structure about the front pillar of a road vehicle. The simulated results are assessed by comparison with the acoustic theory and reveal fairly well the dependence of the predicted surface pressure fluctuations upon the vehicle cruising speed with the sixth power law. The features of three dimensional vortical flow are clarified from the analysis of the simulated results, indicating the strong relationship between the vortical formation and the external pressure fluctuations on the front side window surface. The external pressure fluctuations seem to be strongly related to the vortex breakdown during its interaction with the front side window and the roof-side window junction.