Search Results

In this study, we determined the detailed reaction mechanism of CO/NO/O2 for automotive three way catalysts. The N2O formation process obtained from measurements of the reaction properties and the formation process of adsorbed NCO species obtained from surface analysis of platinum group metals were added to a previous detailed surface reaction mechanism. The computational accuracy of the developed reaction mechanism was verified by the one-dimensional simulation software BOOST, and it was found to be sufficient for any combination of platinum group metals and gas concentrations.

Automobiles will have to be applied strict regulations such as Euro7 against PM, HC, CO. The generation of these components are related to fuel deposition to the wall surface of the combustion chamber. Therefore, the fuel injection model of engine combustion CFD requires accurate prediction about the deposition and vaporization of fuel on the combustion chamber. In this study, multiphase flow numerical analysis that simulates fuel behavior on the wall surface was conducted first. Then, two model formulae about the contact area and the heat flux of a liquid film was constructed based on the result of multiphase flow numerical analysis method. Finally, the new film heat transfer model was constructed from these model formulae. In addition, it was confirmed that new heat transfer model can predict the liquid film temperature obtained by multiphase flow numerical analysis method accurately.

As a technology to reduce the heat loss of engines, heat insulation coating to the surface of combustion chamber has been received a lot of attention. In order to maximize the thermal efficiency improvements by the technology, it is important to clarify the location where heat insulation coating can reduce heat loss more effectively, considering the impact on abnormal combustion etc. In this study, transient behavior of wall heat flux distribution on the piston was analyzed using 3D Computational Fluid Dynamics (CFD) for three combustion modes (spark ignition combustion (SI), homogenous charge compression Ignition (HCCI) and spark controlled compression ignition (SPCCI)).

It was important for predicting wall heat flux to apply wall heat transfer model by taking into account of the behavior of turbulent kinetic energy and density change in wall boundary layer. Although energy equation base wall heat transfer model satisfied above requirements, local physical amounts such as turbulent kinetic energy in near wall region should be applied. In this study, in order to predict wall heat transfer by zero dimensional analysis, how to express wall heat transfer by using mean physical amounts in engine combustion chamber was considered by experimental and numerical approaches.

Control of self-ignition timing in a HCCI engine is still a major technical issue. Recently, the application of a non-equilibrium plasma using repetitively discharge has been proposed as the promising technology. However, non-equilibrium plasma reaction in higher hydrocarbon fuel mixture is very complicated. Hence, there have been few calculation reports considering a series of reactions from non-equilibrium plasma production to high temperature oxidation process. In this study, 0-dimensional numerical simulation model was developed in which both reactions of plasma chemistry and high temperature oxidation combustion was taken into account simultaneously. In addition, an ODEs solver has been applied for the reduction of calculation time in the simulation. By comparing calculation results with experiment such as self-ignition timing, the validity of the developed numerical model has been evaluated.

In the development of fuel tank systems, it is important to maintain fuel system integrity even if a car accident occurs. When a fuel tank undergoes a sudden change in velocity, the fuel starts to move and deforms the tank walls and baffle plates, and then the deformation changes the flow pattern of fuel. Because interaction of fuel with tank components is the main cause of fuel spillage upon crash, it is important to predict complex fluid-structure interaction responses at an early stage of crash safety development with a multiphysics simulation. Development of the multiphysics simulation technique was conducted stepwise by examining “fluid motion” and “tank deformation.” First, a sled test of a rigid-wall tank with observation window was conducted to evaluate the fluid motion inside the tank. A numerical model was developed based on an ALE (Arbitrary Lagrangian Eulerian) algorithm for the fluid and a Lagrangian algorithm for the structure.

On-road turbulences caused by sources such as atmospheric wind and other vehicles influence the flow field and increases the drag in a vehicle. In this study, we focused on a scenario involving a passing vehicle and investigated its effect on the physical mechanism of the drag increase in order to establish a technique for reducing this drag. Firstly, we conducted on-road measurements of two sedan-type vehicles passed by a truck. Their aerodynamic drag estimated from the base pressure measurements showed different increment when passed by the truck. This result raised the possibility of reducing the drag increase by a modification of the local geometry. Then, we conducted wind tunnel measurements of a simplified one-fifth scale vehicle model in quasi-steady state, in order to understand the flow mechanism of the drag increase systematically.

A road vehicle’s cornering motion is known to be a compound motion composed mainly of forward, sideslip and yaw motions. But little is known about the aerodynamics of cornering because little study has been conducted in this field. By clarifying and understanding a vehicle’s aerodynamic characteristics during cornering, a vehicle’s maneuvering stability during high-speed driving can be aerodynamically improved. Therefore, in this study, the aerodynamic characteristics of a vehicle’s cornering motion, i.e. the compound motion of forward, sideslip and yaw motions, were investigated. We also considered proposing an aerodynamics evaluation method for vehicles in dynamic maneuvering. Firstly, we decomposed cornering motion into yaw and sideslip motions. Then, we assumed that the aerodynamic side force and yaw moment of a cornering motion could be expressed by superposing linear expressions of yaw motion parameters and those of sideslip motion parameters, respectively.

A mixed time-scale subgrid large eddy simulation was used to simulate mixture formation, combustion and soot formation under the influence of turbulence during diesel engine combustion. To account for the effects of engine wall heat transfer on combustion, the KIVA code's standard wall model was replaced to accommodate more realistic boundary conditions. This were carried out by implementing the non-isothermal wall model of Angelberger et al. with modifications and incorporating the log law from Pope's method to account for the wall surface roughness. Soot and NOx emissions predicted with the new model are compared to experimental data acquired under various EGR conditions.

The present study investigated the aerodynamic pitching stability of sedan-type vehicles under the influence of A- and C-pillar geometrical configurations. The numerical method used for the investigation is based on the Large Eddy Simulation (LES) method. Whilst, the Arbitrary Lagrangian-Eulerian (ALE) method was employed to realize the prescribed pitching oscillation of vehicles during dynamic pitching and fluid flow coupled simulations. The trailing vortices that shed from the A-pillar and C-pillar edges produced the opposite tendencies on how they affect the aerodynamic pitching stability of vehicles. In particular, the vortex shed from the A-pillar edge tended to enhance the pitching oscillation of vehicle, while the vortex shed from the C-pillar edge tended to suppress it. Hence, the vehicle with rounded A-pillar and angular C-pillar exhibited a higher aerodynamic damping than the vehicle with the opposite A- and C-pillars configurations.

In the present study, numerical simulation coupling convection and radiation in vehicle was done to analyze the formation of the temperature field under the non-uniform thermal condition. The scaled cabin model of simplified compact car was used and the thermal condition was determined. The fore floor, the top side of the inst. panel, the front window and the ceiling were heat source. The lateral side walls were cooled by the outdoor air and the other surfaces were adiabatic. It is same with the experimental condition presented in Part 5. In order to analyze the individual influence of each heat source, Contribution Ratio of Indoor climate (CRI) index was used. CRI is defined as the ratio of the temperature rise at a point from one individual heat source to the temperature rise under the perfect mixing conditions for the same heat source.

Experimental and computational studies were carried out to characterize the spray development and evaporation processes of multi-hole injector for direct injection spark ignition (DISI) engines. The main injector parameter to be investigated in this study is a diverging angle between neighboring two holes. In the experimental study, the influence of the diverging angle on evaporation process of fuel spray from two-hole injector was investigated using Laser Absorption Scattering (LAS) measurement. Smaller diverging angle causes larger spray tip penetration because the momentum of the spray from one hole emphasizes another, when two spray merge to one. Moreover, spray tip penetration decreases at certain diverging angle due to the negative pressure region between two sprays. Mechanisms behind the above spray behaviors were discussed using the detailed information on the spray and ambient gas flow fields obtained by the three dimensional computational fluid dynamics (CFD).

In the present study, two kinds of simplified vehicle models, which can reproduce flow structures around the two sedan-type vehicles in the previous study, are constructed for the object and the unsteady flow structures are extracted using Large-Eddy Simulation technique. The numerical results are validated in a stationary condition by comparing the results with a wind-tunnel experiment and details of steady and unsteady flow characteristics around the models, especially above the trunk deck, are investigated. In quasi- and non- stationary manner with regard to vehicle pitch motion, unsteady flow characteristics are also investigated and their relations to an aerodynamic stability are discussed.

In the present study, a model experiment is performed in order to clarify the ventilation characteristics of car cabin. This study also provides high precision data for benchmark test. As a first step, the ventilation mode is tested, which is one of the representative air-distribution modes. Part 1 describes the properties of the flow field in the cabin obtained by the experiment. Part 2 describes the ventilation efficiencies such as the age of air by using trace gas method. The properties of flow field are measured using particle image velocimetry (PIV). The mean velocity profiles, the standard deviation distribution, and the turbulence intensity distribution are discussed. The brief comparison between experiments and predictions of computational fluid dynamics (CFD) is also presented. In the comparison between experiment and CFD, the results showed similar flow field.

The present study had two aims: (1) to develop a model which reproduced the dummy lower leg kinematics observed in a high-speed test, and (2) to develop a methodology to assess various theoretical design parameters of a heel foam pad to reduce the risk of the lower extremity injuries. To address the first aim, a MADYMO sled simulation model was developed. The interior parts were represented mainly with finite element (FE) models, with intent to capture deformations and the reaction force directions. Moreover, the occupant responses were estimated from the refined version of the dummy model (i.e., the Hybrid III model; Q dummy model). The model was acceptably correlated to experiments. To address the second aim, the model was simplified for subsequent optimization of the heel foam pad.

An experimental and numerical study was conducted on the spray and mixture properties of a hole-type injector for direct injection (D. I.) gasoline engines. The Laser Absorption Scattering (LAS) technique was adopted to simultaneously measure the spatial concentration distributions and the mass of the liquid and vapor phases in the fuel spray injected into a high-pressure and high-temperature constant volume vessel. The experimental results were compared to the numerical calculation results using three-dimensional CFD and the multi-objective optimization. In the numerical simulation, the design variable of the spray model was optimized by choosing spray tip penetration, and mass of liquid and vapor phases as objective functions.

Continuous improvement of side airbag safety performance is an important step because it is associated with many public domain tests and regulations. Thus, occupant restraint with a side airbag is critical and it is necessary to develop tools that can be utilized to help in design of side airbags. Though many papers on side impact safety have been published, only a few papers are related to MADYMO simulations of side airbags. This paper describes an improved injury prediction and optimization approach using a MADYMO model for side impact. This model consists of 3 parts: dummy, trim and airbag in FEM. In this study, a side impact with a ES-2, EuroSID-2, was simulated in MADYMO as follows: First, component tests were conducted for trim and airbag respectively to establish correlation. Second, these component models were then integrated into a MADYMO model, which has high correlation with a crash simulator that is capable of replicating physical vehicle tests.

Concept of the spray guided direct Injection spark ignition (DISI) was studied to improve the performance of wall-guided DISI. Focusing the effect of multi-hole injector location either centrally-mounted or side-mounted, mixture distribution and ignitability was studied. Computational Fluid Dynamics (CFD) modeling was applied to investigate the history of mixture, ignitable mixture existence around the spark plug in light load condition and homogeneity in full load condition. CFD results showed that side-mounted injection has an advantage over centrally-mounted injection in terms of mixture stability around the spark plug, although the slight disadvantage in homogeneity in full load condition. Side-mounted injection was selected because of robust ignitability potential and further experimental investigation was conducted. Stable combustion window against injection and ignition timing was investigated in experimentally.

Experiment and CFD have been performed to clarify the distribution of wind noise sources and its generation mechanism for a production vehicle. Three noise source identification techniques were applied to measure the wind noise sources from the outside and inside of vehicle. The relation between these noise sources and the interior noise was investigated by modifying the specification of underbody and front-pillar. In addition, CFD was preformed to predict the noise sources and clarify its generation mechanism. The noise sources obtained by simulation show good agreement with experiment in the region of side window and underbody.

Some of the frequencies of transmission gear whine noise reach up to several kHz. High-frequency gear whine noise is mostly transmitted by air (airborne); therefore, it is critical to reduce transmission radiation noise. This paper presents how to solve the problem of high-frequency noise in the range of 2.0 - 4.1kHz by experiment using Inverse Boundary Element Method (IBEM) and by computer simulation using Boundary Element Method (BEM).