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Technical Paper

Analysis of Flow Induced Noise in a Passenger Car Exhaust System - An Experimental and Numerical Approach

2011-05-17
2011-01-1528
A muffler or silencer is an integral part of the exhaust system and is a device used to prevent sound from reaching the openings of the exhaust duct and radiating as far field noise. Different acoustical design and analysis techniques are used to predict the acoustical performance of exhaust systems. Flow noise from exhaust tail pipe is one of the major noise sources in a vehicle. Flow noise is generated mainly during fast acceleration operating condition due to complex flow behavior. In this paper, we have studied the detailed flow field and tried to establish an analyses procedure for flow noise prediction. The flow analysis is carried out in commercial CFD solver Star CCM+. The transient engine boundary conditions are obtained from the experimental testing. The flow noise generated from the muffler was calculated by acoustic analogy of Lighthill using the above boundary conditions.
Journal Article

Two-Dimensional In-Cylinder Soot Volume Fractions in Diesel Low Temperature Combustion Mode

2011-04-12
2011-01-1390
Soot Volume Fraction (SVF) measurements were performed in an IFP Energies nouvelles optical single cylinder Diesel engine operated in Low Temperature Combustion (LTC) conditions. The engine was equipped with a sapphire liner, a dedicated flat bowl piston and a six-hole common-rail high pressure injector. The piston design included four quartz windows allowing optical access into the bowl. The aim of this work was to study soot formation and oxidation during the LTC Diesel combustion process and to build a database providing soot formation and oxidation data under a set of engine conditions to help developing and testing Computational Fluid Dynamics (CFD) models. Two complementary optical diagnostic techniques were combined: Planar Laser Induced Incandescence (PLII) and Laser Extinction Method (LEM).
Technical Paper

CFD Analysis of Oil/Gas Flow in Piston Ring-Pack

2011-04-12
2011-01-1406
The oil consumption and blow-by are complex phenomena that need to be minimized to meet the ever changing modern emission standards. Oil flows from the sump to the combustion chamber and the blow-by gases flow from the combustion chamber to the crank case. There are several piston rings on the piston, which form a ring-pack. The ring pack has to be efficiently designed to minimize the oil consumption and blow-by. Since it is difficult and extremely costly to conduct experiments on every series of engines to check for the blow-by and oil consumption, a CFD analysis can be performed on the ring pack to study the blow-by and oil-consumption characteristics. In the CFD analysis described here, the region considered is between the compression chamber and the skirt, between the piston (including the rings) and the cylinder liner. The 3D CFD analysis was conducted for the engine running conditions of 5000 rpm and load of 13.5 kPa, for a 2.4L gasoline engine.
Journal Article

Direct Aeroacoustic Simulation of Flow Impingement Noise in an Exhaust Opening

2011-05-17
2011-01-1517
Unusual noises during vehicle acceleration often reflect poorly on customer perception of product quality and must be removed in the product development process. Flow simulation can be a valuable tool in identifying root causes of exhaust noises created due to tailpipe openings surrounded by fascia structure. This paper describes a case study where an unsteady Computational Fluid Dynamics (CFD) simulation of the combined flow and acoustic radiation from an exhaust opening through fascia components provided valuable insight into the cause of an annoying flow noise. Simulation results from a coupled thermal/acoustic analysis of detailed tailpipe opening geometry were first validated with off-axis microphone spectra under wide open throttle acceleration. After studying the visualizations of unsteady flow velocity and pressure from the CFD, a problem that had proved difficult to solve by traditional “cut and try” methods was corrected rapidly.
Technical Paper

Microkinetic Modelling for Propane Oxidation in Channel Flows of a Silver-Based Automotive Catalytic Converter

2011-08-30
2011-01-2094
Computational Fluid Dynamics (CFD) is used to simulate chemical reactions and transport phenomena occurring in a single channel of a honeycomb-type automotive catalytic converter under lean burn combustion. Microkinetic analysis is adopted to develop a detailed elementary reaction mechanism for propane oxidation on a silver catalyst. Activation energies are calculated based on the theory of the Unity Bond Index-Quadratic Exponential Potential (UBI-QEP) method. The order-of-magnitude of the pre-exponential factors is obtained from Transition State Theory (TST). Sensitivity analysis is applied to identify the important elementary steps and refine the pre-exponential factors of these reactions. These pre-exponential factors depend on inlet temperatures and propane concentration; therefore optimised pre-exponential factors are written in polynomial forms. The results of numerical simulations are validated by comparison with experimental data.
Technical Paper

Visualization of the Cavitating Flow inside the Nozzle Hole Using by Enlarged Acrylic Nozzle

2011-08-30
2011-01-2062
In this study, it is purpose to make clear the effect of cavitation phenomenon on the spray atomization. In this report, the cavitation phenomenon inside the nozzle hole was visualized and the pressure measurements along the wall of the nozzle hole were carried out by use of 25-times enlarged acrylic nozzle. For the representatives of regular gasoline, single and two-component fuels were used as a test fuel. In addition, various cavitating flow patterns same as experimental conditions were simulated by use of Barotropic model incorporated in commercial code of Star-CD scheme, and compared with experimental results.
Technical Paper

An Ultimate Engine: designed by Computational Fluid Dynamics

2011-08-30
2011-01-2027
A single lightweight engine capable of operating over a wide range of Mach numbers from startup to the hypersonic regime is proposed for automobiles and airplanes. Traditional piston engines, turbojet engines, and scram jet engines operate only under a narrower range of conditions. A compression system of colliding super multijets is proposed instead of a traditional turbofan. This ultimate engine system can be extended with a special piston system to achieve an improved fuel consumption rate, while maintaining a low noise level.
Technical Paper

Aerodynamic Effects of Roof Deflector and Cab Side Extenders for Truck-Trailer Combinations

2011-09-13
2011-01-2284
Today there are a large variety of drag-reducing devices for heavy trucks that are commonly used, for example, roof deflectors, cab side extenders and chassis fairings. These devices are often proven to be efficient, reducing the total aerodynamic resistance for the vehicle. However, the drag-reducing devices are usually identical for a specific pulling vehicle, independent of the layout of the vehicle combination. In this study, three vehicle combinations were analyzed. The total length of the vehicles varied between 10.10 m and 25.25 m. The combinations consisted of a rigid truck in combination with one or two cargo units. The size of the gap between the cargo units differed between the vehicle combinations. There were also three configurations of each vehicle combination with different combinations of roof deflector and cab side extenders, yielding a total number of nine configurations.
Technical Paper

Interior Noise Prediction and Analysis of Heavy Commercial Vehicle Cab

2011-09-13
2011-01-2241
The basic theory of statistical energy analysis (SEA) is introduced, a commercial heavy duty truck cab is divided into 35 subsystems applying SEA method, and a three dimensional SEA model of the commercial heavy duty truck cab is created. Three basic parameters including modal density, damping loss factor and coupling loss factor are calculated with analytical and experimental methods. The modal density of the regular wall plate of the cab is calculated with traditional formula. The damping loss factors of the regular and complicated plates are obtained using analytical method and steady energy stream method. Meanwhile, the coupling loss factors of structure-structure, structure-sound cavity, and cavity-cavity are also calculated. Four kinds of excitations are in the SEA model, including sound radiation excitation of engine, engine mount vibration excitation, road excitation and wind excitation.
Technical Paper

Detailed Chemistry CFD Engine Combustion Solution with Ignition Progress Variable Library Approach

2009-06-15
2009-01-1898
This paper explains the principle and advantages of the Ignition Progress Variable Library (IPV-Library) approach and its use in predicting engine related premixed, non-premixed and compression ignited combustion events. The implementation of IPV-Library model in the engine-focused CFD code VECTIS is described. To demonstrate the application of the model in predicting various types of combustion, computational results from a 2-stroke HCCI engine, a premixed spark ignition engine and an HSDI diesel engine are presented, together with some comparisons with engine test data.
Technical Paper

Diesel Combustion Model with Auto-ignition Process of Non-homogeneous Mixture

2009-06-15
2009-01-1897
Diesel combustion model for CFD simulation is established taking account of an auto-ignition process of non-homogeneous mixture. Authors revealed in their previous paper that the non-homogeneity of fuel-air mixture affected more on auto-ignition process such as its ignition delay or combustion duration than the turbulent mixing rate. Based on these results, novel diesel combustion model is proposed in this study. The transport calculation for local variation of fuel-air PDF is introduced and the chemical reaction rate is provided by the local non-homogeneity. Furthermore, this model is applied the RANS based CFD simulation of the spray combustion in a Diesel engine condition. The results show that the combustion process is well described for several engine operations.
Journal Article

Applications of CFD Modeling in GDI Engine Piston Optimization

2009-06-15
2009-01-1936
This paper describes a CFD modeling based approach to address design challenges in GDI (gasoline direct injection) engine combustion system development. A Ford in-house developed CFD code MESIM (Multi-dimensional Engine Simulation) was applied to the study. Gasoline fuel is multi-component in nature and behaves very differently from the single component fuel representation under various operating conditions. A multi-component fuel model has been developed and is incorporated in MESIM code. To apply the model in engine simulations, a multi-component fuel recipe that represents the vaporization characteristics of gasoline is also developed using a numerical model that simulates the ASTM D86 fuel distillation experimental procedure. The effect of the multi-component model on the fuel air mixture preparations under different engine conditions is investigated. The modeling approach is applied to guide the GDI engine piston designs.
Technical Paper

Analysis of Air/Cavitation Interaction Inside a Rotary Vane Pump for Application on Heavy Duty Engine

2009-06-15
2009-01-1943
This paper deals with a CFD three-dimensional multiphase simulation of rotary vane pump. The paper presents a suitable methodology for the investigation of the cavitation effects and/or incondensable gases. All the 3D simulations were performed by using Fluent v12 (Beta version). A moving mesh methodology was defined to reproduce the change-in-time shape of the internal pump volumes. In particular, the pump analysis was focused on the generation, and evolution of the cavitation phenomena inside the machine to identify the locations where this phenomena could occur. Moreover, the influence of incondensable gas dissolved inside the operator fluid on both pump performance and cavitation evolution was evaluated. Significant results were obtained about the analysis of incondensable gas influence on the cavitation evolution showing that, today, CFD analysis can provide detailed information on such harmful phenomena which can not be achieved by experiments.
Technical Paper

A Multi-dimensional Flamelet Model Framework Applied to Split-injection DI Diesel Engines

2009-06-15
2009-01-1917
A general model framework for investigating various injection strategies in compression ignition engines with both mixture and thermal inhomogeneities is presented using an extended representative interactive flamelet model. The equations describing evolution of chemistry are written for a scalar phase space of either one or two dimensions and an approach for modeling multiple injections is given. The combustion model is solved interactively with the turbulent flow field by coupling with a Reynolds-Averaged Navier-Stokes (RANS) solver. The model is applied in the simulation of a split-injection diesel engine and results are compared to experimental data obtained from a single cylinder research engine.
Technical Paper

Hydrogen Low-pressure Gaseous Direct Injection

2009-06-15
2009-01-1924
A low-pressure hydrogen direct-injection solution is presented that allows some typical benefits of direct injection, such as high specific power and backfire prevention, plus low residual storage pressure, that improves vehicle range and is a typical advantage of external mixture formation. Since the injection must end early enough to allow good charge homogeneity and, in any case, before in-cylinder pressure rise constraints hydrogen admission, especially at heavy loads hydrogen flow to the cylinder is higher than present electro-injectors allow. The injection is realised in two steps: hydrogen flow rate is simply controlled by a conventional CNG electro-injector that feeds a small intermediate chamber. From this chamber hydrogen next enters the cylinder in a short crank angle period by means of a mechanically-actuated valve that opens at the intake valve closure to avoid backfire.
Technical Paper

High Density-Low Temperature Combustion in Diesel Engine Based on Technologies of Variable Boost Pressure and Intake Valve Timing

2009-06-15
2009-01-1911
A concept of high density-low temperature combustion (HD-LTC) is put forward in this paper, showing potential of its high thermal efficiency and very low engine-out emissions by engine experimental and CFD modeling study. A single cylinder test engine has been built-up equipped with mechanisms of variable boost pressure and intake valve closing timing (IVCT). By delaying IVCT and raising boost pressure to certain values according to engine loads, the in-cylinder charge density is regulated much higher than in conventional engines. It is found that the high charge density can play the role of rising of heat capacity as exhaust gas recirculation (EGR) does. Thereby low temperature combustion is realized with less EGR (about 18~19% oxygen concentration) to achieve very low NOx and soot emissions, which is extremely important at high and full loads.
Journal Article

Spray Pattern Optimization for the Duratec 3.5L EcoBoost Engine

2009-06-15
2009-01-1916
A systematic methodology has been employed to develop the Duratec 3.5L EcoBoost combustion system, with focus on the optimization of the combustion system including injector spray pattern, intake port design, piston geometry, cylinder head geometry. The development methodology was led by CFD (Computational Fluid Dynamics) modeling together with a testing program that uses optical, single-cylinder, and multi-cylinder engines. The current study shows the effect of several spray patterns on air-fuel mixing, in-cylinder flow development, surface wetting, and turbulence intensity. A few sets of injector spray patterns are studied; some that have a wide total cone angle, some that have a narrow cone angle and a couple of optimized injector spray patterns. The effect of the spray pattern at part load, full load and cold start operation was investigated and the methodology for choosing an optimized injector is presented.
Technical Paper

Advances in Variable Density Wall Functions for Turbulent Flow CFD-Simulations, Emphasis on Heat Transfer

2009-06-15
2009-01-1975
A new variable density / physical property wall function formalism has been developed. The new formalism is designed to extend the validity range of wall functions to cover both the low- and high-Reynolds-number domains so that the restrictions on the non-dimensional near-wall mesh resolution can be avoided. The new formalism also accounts for the temperature gradient induced variations of density, viscosity, heat conductivity and specific heat capacity. The new wall function formalism is constructed in conjunction with a modified low-Reynolds-number turbulence model in order to avoid the conflicting requirements of low- and high-Reynolds-number models on the near wall mesh resolution. The new formulation is validated with test simulations of strongly heated air flows in circular tube against measurements and Direct Numerical Simulation (DNS) results.
Journal Article

Applying an Interactively Coupled CFD-Multi-Zone Approach to Study the Effects of Piston Bowl Geometry Variations on PCCI Combustion

2009-06-15
2009-01-1955
Recently, a consistent mixing model for the two-way coupling of a CFD code and a zero-dimensional multi-zone code was developed. This work allowed for building an interactively coupled CFD-multi-zone approach that can be used to model HCCI combustion. In this study, the interactively coupled CFD-multi-zone approach is applied to PCCI combustion in a 1.9l FIAT GM Diesel engine. The physical domain in the CFD code is subdivided into multiple zones based on one phase variable (fuel mixture fraction). The fuel mixture fraction is the dominant quantity for the description of nonpremixed combustion. Each zone in the CFD code is represented by a corresponding zone in the zero-dimensional multi-zone code. The zero-dimensional multi-zone code solves the chemistry for each zone, and the heat release is fed back into the CFD code. The thermodynamic state of each zone, and thereby the phase variable, changes in time due to mixing and source terms (e.g., vaporization of fuel, wall heat transfer).
Technical Paper

Scattering Matrix Evaluation with CFD in Low Mach Number Flow Ducts

2009-05-19
2009-01-2040
We present an efficient methodology to perform calculations of acoustic propagation and scattering by components in ducts with flows. In this paper a methodology with a linearized Navier-Stokes equations solver in frequency domain is evaluated on a two-dimensional geometry of an in-duct area expansion. The Navier-Stokes equations are linearized around a time-independent mean flow that is obtained from an incompressible Reynolds Averaged Navier-Stokes solver which uses a k-ε turbulence model and adaptive mesh refinement. A plane wave decomposition method based on acoustic pressure and velocity is used to extract the up and downstream propagating waves. The reflection of the acoustic waves by the induct area expansion is calculated and compared to both measurements and analytical models. Frequencies in the plane wave range up to the cut-on frequency of the first higher order propagating acoustical mode are considered.
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