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Cooling Airflow System Modeling in CFD Using Assumption of Stationary Flow

2011-11-29
Today CFD is an important tool for engineers in the automotive industry who model and simulate fluid flow. For the complex field of Underhood Thermal Management, CFD has become a very important tool to engineer the cooling airflow process in the engine bay of vehicles. Presenter Peter Gullberg, Chalmers University of Technology
Technical Paper

Flow Visualization Study of an HVAC Module Operated in Water

2001-05-14
2001-01-1702
Centrifugal blowers serve as the primary source of airflow and aero-acoustic noise in automotive HVAC modules. Flow field measurements inside blowers indicate very complex flow patterns. A detailed flow visualization study was conducted on an actual HVAC fan module operated in water under dynamically similar conditions as those in air with the purpose of studying the complex flow patterns in order to improve the aerodynamic performance of the fan/scroll casing and diffuser components. Fan-scroll/diffuser interaction was also studied as function of fan speed. Conventional and special (shear thickening) dye injection flow visualization techniques were used to study the complex 3-dimensional vortical and unsteady flow patterns that occur in typical HVAC fans. A major advantage of the flow visualization technique using shear-thickening dye is its usefulness in high the Reynolds number flows that are typically encountered inside HVAC modules.
Technical Paper

Experimental Study of the Combustion Process in a Heavy–Duty DI Diesel Engine for Different Injection Scenarios

2003-05-19
2003-01-1783
The effects of injection pressure and duration on exhaust gas emissions, sooting flame temperature, and soot distribution for a heavy–duty single cylinder DI diesel engine were investigated experimentally. The experimental analysis included use of two–color pyrometry as well as “conventional” measuring techniques. Optical access into the engine was obtained through an endoscope mounted in the cylinder head. The sooting flame temperature and soot distribution were evaluated from the flame images using the AVL VisioScope™ system. The results show that the NOx/soot trade–off curves could be improved by increasing injection pressure. An additional reduction could also be obtained if, for the same level of injection pressure, the injection duration was prolonged.
Technical Paper

Turbulent Flame Speed Closure Model: Further Development and Implementation for 3-D Simulation of Combustion in SI Engine

1998-10-19
982613
A Turbulent Flame Speed Closure Model is modified and implemented into the FIRE code for use in 3D computations of combustion in an SI-engine. The modifications are done to account for mixture inhomogeneity, and mixture compression through the dependency of local equivalence ratio, pressure and temperature on the chemical time scale and a global reaction time scale. The model is also subjected to further evaluation against experimental data, covering different mixture and turbulence conditions. The combustion process in a 4-valve pentroof combustion chamber is simulated and heat release rates and spatial flame distribution are evaluated against experimental data. The computations show good agreement with the experiments. The model has proven to be a robust and time effective simulation tool with good predictive ability.
Technical Paper

Oxidation of Hydrocarbons Released from Piston Crevices of S.I. Engines

1995-10-01
952539
This work presents a numerical method for predictions of HC oxidation in the cold turbulent wall jet emerging from the piston top land crevice in an S.I. engine, using a complex chemical reaction model. The method has been applied to an engine model geometry with the aim to predict the HC oxidation rate under engine - relevant conditions. According to the simulation a large amount of HC survives oxidation due to the long ignition delay of the wall jet emitted from the crevice. This ignition delay, in turn depends mainly on chemical composition and temperature of the gas mixture in the crevice and also on the temperature distribution in the cylinder boundary layer.
Technical Paper

Comparison of Cylinder Pressure Based Knock Detection Methods

1997-10-01
972932
Eight different cylinder pressure trace based knock detection methods are compared using two reference cycles of different time-frequency content, reflecting single blast and developing blast, and a test population of 300 knocking cycles. It is shown that the choice of the pass window used for the pressure data has no significant effect on the results of the different methods, except for the KI20. In contrast to other authors, no sudden step in the knock characteristics is expected; first, because the data investigated contain only knocking cycles, and second, because a smooth transition between normal combustion and knock is expected, according to recent knock theory. It is not only the correlation coefficient, but also the Kendall coefficient of concordance, that is used to investigate the differences between the knock classification methods.
Technical Paper

Injection Orifice Shape: Effects on Combustion and Emission Formation in Diesel Engines

1997-10-01
972964
A series of experimental studies of diesel spray combustion was carried out using non-circular and back-step orifices. The experiments were performed in a single-cylinder engine and in a constant volume combustion chamber. In the engine tests, elliptic orifices with an aspect ratio of approximately 2:1 were compared with circular orifices. The elliptic orifices had sharp inlets and the circular orifices had rounded inlets. Elliptic orifices aligned with either the minor axis or the major axis in the direction of the nozzle tip were tested. The orifice shapes had minor effects on the heat release, ignition delay, and emissions of smoke, CO and HC. However, substantial differences were observed for emissions of NOx: for the vertical elliptic orifices, emissions up to 37.6 percent lower than with circular orifices were observed. In the combustion bomb tests, rectangular and back-step orifices were compared with circular orifices, all with sharp inlets.
Technical Paper

Knock in Spark-Ignition Engines: End-Gas Temperature Measurements Using Rotational CARS and Detailed Kinetic Calculations of the Autoignition Process

1997-05-01
971669
Cycle-resolved end-gas temperatures were measured using dual-broadband rotational CARS in a single-cylinder spark-ignition engine. Simultaneous cylinder pressure measurements were used as an indicator for knock and as input data to numerical calculations. The chemical processes in the end-gas have been analysed with a detailed kinetic mechanism for mixtures of iso-octane and n-heptane at different Research Octane Numbers (RON'S). The end-gas is modelled as a homogeneous reactor that is compressed or expanded by the piston movement and the flame propagation in the cylinder. The calculated temperatures are in agreement with the temperatures evaluated from CARS measurements. It is found that calculations with different RON'S of the fuel lead to different levels of radical concentrations in the end-gas. The apperance of the first stage of the autoignition process is marginally influenced by the RON, while the ignition delay of the second stage is increased with increasing RON.
Technical Paper

Using Multi-Rate Filter Banks to Detect Internal Combustion Engine Knock

1997-05-01
971670
The wavelet transform is used in the analysis of the cylinder pressure trace and the ionic current trace of a knocking, single-cylinder, spark ignition engine. Using the wavelet transform offers a significant reduction of mathematical operations when compared with traditional filtering techniques based on the Fourier transform. It is shown that conventional knock analysis in terms of average energy in the time domain (AETD), corresponding to the signal's energy content, and maximum amplitude in the time domain (MATD), corresponding to the maximum amplitude of the bandpass filtered signal, can be applied to both the reconstructed filtered cylinder pressure and the wavelet coefficients. The use of the filter coefficients makes possible a significant additional reduction in calculation effort in comparison with filters based on the windowed Fourier transform.
Technical Paper

A Model of Turbocharged Engines as Dynamic Drivetrain Members

1993-11-01
933050
An engine model for use in computer simulation of transient behavior in drivetrain and vehicle systems is presented. Two elements, important for deviation (e.g. turbo-lag) from steady state characteristics, are the inertia of the supercharging unit (turbo shaft) and the fuel injection control system. No extensive combustion calculations are carried out within the model. Instead it uses condensed results from existing combustion models and measurements. The model is semi-empirical. Some of the engine specific properties needed for simulation are (e.g. for a turbocharged diesel): engine data in steady state operation, mappings of compressor and turbine performance, inertia of the engine components condensed to the crankshaft, turbo shaft inertia, displacement, compression ratio and the essentials of the fuel injection control strategy. Input parameters to the computer program based on the model are accelerator pedal position and external torque acting on the flywheel.
Technical Paper

Impact of Conventional and Electrified Powertrains on Fuel Economy in Various Driving Cycles

2017-03-28
2017-01-0903
Many technological developments in automobile powertrains have been implemented in order to increase efficiency and comply with emission regulations. Although most of these technologies show promising results in official fuel economy tests, their benefits in real driving conditions and real driving emissions can vary significantly, since driving profiles of many drivers are different than the official driving cycles. Therefore, it is important to assess these technologies under different driving conditions and this paper aims to offer an overall perspective, with a numerical study in simulations. The simulations are carried out on a compact passenger car model with eight powertrain configurations including: a naturally aspirated spark ignition engine, a start-stop system, a downsized engine with a turbocharger, a Miller cycle engine, cylinder deactivation, turbocharged downsized Miller engine, a parallel hybrid electric vehicle powertrain and an electric vehicle powertrain.
Technical Paper

Heavy Duty Diesel Engine Modeling with Layered Artificial Neural Network Structures

2018-04-03
2018-01-0870
In order to meet emissions and power requirements, modern engine design has evolved in complexity and control. The cost and time restraints of calibration and testing of various control strategies have made virtual testing environments increasingly popular. Using Hardware-in-the-Loop (HiL), Volvo Penta has built a virtual test rig named VIRTEC for efficient engine testing, using a model simulating a fully instrumented engine. This paper presents an innovative Artificial Neural Network (ANN) based model for engine simulations in HiL environment. The engine model, herein called Artificial Neural Network Engine (ANN-E), was built for D8-600 hp Volvo Penta engine, and directly implemented in the VIRTEC system. ANN-E uses a combination of feedforward and recursive ANNs, processing 7 actuator signals from the engine management system (EMS) to provide 30 output signals.
Technical Paper

Numerical Analysis of NOx Formation Trends in Biodiesel Combustion using Dynamic ϕ-T Parametric Maps

2011-08-30
2011-01-1929
The use of biodiesel in conventional diesel engines results in increased NOx emissions; this presents a barrier to the widespread use of biodiesel. The origins of this phenomenon were investigated using the CFD KIVA3V code, which was modified to account for the physical properties of biodiesel and to incorporate semi-detailed mechanisms for its combustion and the formation of emissions. Parametric φ-T maps and 3D engine simulations were used to assess the impact of using oxygen-containing fuels on the rate of NO formation. It was found that using oxygen-containing fuels allows more O₂ molecules to present in the engine cylinder during the combustion of biodiesel, and this may be the cause of the observed increase in NO emissions.
Technical Paper

Cooling Airflow System Modeling in CFD Using Assumption of Stationary Flow

2011-09-13
2011-01-2182
Today CFD is an important tool for engineers in the automotive industry who model and simulate fluid flow. For the complex field of Underhood Thermal Management, CFD has become a very important tool to engineer the cooling airflow process in the engine bay of vehicles. To model the cooling airflow process accurately in CFD, it is of utmost importance to model all components in the cooling airflow path accurately. These components are the heat exchangers, fan and engine bay blockage effect. This paper presents CFD simulations together with correlating measurements of a cooling airflow system placed in a test rig. The system contains a heavy duty truck louvered fin radiator core, fan shroud, fan ring and fan. Behind the cooling module and fan, a 1D engine silhouette is placed to mimic the blockage done by a truck engine. Furthermore, a simple hood is mounted over the module to mimic the guiding of air done by the hood shape in an engine bay.
Technical Paper

Modeling, Identification, and Separation of Crankshaft Dynamics in a Light-Duty Diesel Engine

2009-06-15
2009-01-1798
Mathematical models of a torque sensor equipped crankshaft in a light-duty diesel engine are identified, validated, and compared. The models are based on in-cylinder pressure and crankshaft torque data collected from a 5-cylinder common-rail diesel engine running at multiple operating points. The work is motivated by the need of a crankshaft model in a closed-loop combustion control system based on crankshaft torque measurements. In such a system a crankshaft model is used in order to separate the measured crankshaft torque into cylinder individual torque contributions. A method for this is described and used for IMEP estimation. Not surprisingly, the results indicate that higher order models are able to estimate crankshaft torque more accurately than lower order models, even if the differences are small. For IMEP estimation using the cylinder separation method however, these differences have large effects on accuracy.
Technical Paper

A Novel Concept for Combined Hydrogen Production and Power Generation

2009-06-15
2009-01-1946
A novel concept of combined hydrogen production and power generation system based on the combustion of aluminum in water is explored. The energy conversion system proposed is potentially able to provide four different energy sources, such us pressurized hydrogen, high temperature steam, heat, and work at the crankshaft on demand, as well as to fully comply with the environment sustainability requirements. Once aluminum oxide layer is removed, the pure aluminum can react with water producing alumina and hydrogen while releasing a significant amount of energy. Thus, the hydrogen can be stored for further use and the steam can be employed for energy generation or work production in a supplementary power system. The process is proved to be self-sustained and to provide a remarkable amount of energy available as work or hydrogen.
Technical Paper

An Investigation and Correction Method of Stationary Fan CFD MRF Simulations

2009-10-01
2009-01-3067
A common fan model to use in automotive under hood simulations is the Multiple Reference Frame (MRF) model and within the industry, for this specific application, this model is well known to under predict performance. In a former paper, referenced 2009-01-0178, a simple “speed correction” of the MRF model was proposed by the authors'. The correction was shown to apply across different operating speeds for a specific fan. In this paper the generality and limitation of this correction across fans of different type, design and dimensions are investigated. Investigated in this paper is as well the sensitivity of the MRF model to specific methodology of use. In this paper it is shown that the speed correction of 14% proposed in the former paper applies widely, hence, although the MRF model is erroneous the error is consistent.
Technical Paper

A Correction Method for Stationary Fan CFD MRF Models

2009-04-20
2009-01-0178
A common fan model to use in automotive under hood simulations is the Multiple Reference Frame (MRF) model and within the industry, for this specific application, this model is well known to under predict performance. In this paper we have examined the possibilities of correcting this deficiency with a simple “speed correction”. This is done by testing and simulating a production fan in the Volvo Fan Test Rig for two operating speeds, 1200 rpm and 2400 rpm. Pressure rise, fan power and static efficiency are presented as functions of volumetric flow rate. The simulations verify that using the MRF model the common behavior of under predicting pressure rise and performance of the fan occur. In addition, this work shows that; although the MRF is not predicting fan performance correctly it constitutes a reliable fan modeling strategy.
Technical Paper

Combustion and Emissions in a Light-Duty Diesel Engine Using Diesel-Water Emulsion and Diesel-Ethanol Blends

2009-11-02
2009-01-2695
The purpose of the investigation presented here was to compare the effects of fuel composition on combustion parameters, emissions and fuel consumption in engine tests and simulations with five fuels: a Diesel-water emulsion, a Diesel-ethanol blend, a Diesel-ethanol blend with EHN (cetane number improver), a Fischer-Tropsch Diesel and an ultra-low sulfur content Diesel. The engine used in the experiments was a light duty, single cylinder, direct injection, common rail Diesel engine equipped with a cylinder head and piston from a Volvo NED5 engine. In tests with each fuel the engine was operated at two load points (3 bar IMEP and 10 bar IMEP), and a pilot-main fuel injection strategy was applied under both load conditions. Data were also obtained from 3-D CFD simulations, using the KIVA code, to compare to the experimental results and to further analyze the effects of water and ethanol on combustion.
Technical Paper

Axial Fan Performance Predictions in CFD, Comparison of MRF and Sliding Mesh with Experiments

2011-04-12
2011-01-0652
Underhood Thermal Management has become an important topic for the majority of automotive OEM's. To keep combustion engines cool and manage waste heat efficiently is an important part in the design of vehicles with low fuel consumption. To be able to predict cooling performance and underhood airflow with good precision within a virtual design process, it is of utmost importance to model and simulate the cooling fan efficiently and accurately, and this has turned out to be challenging. Simulating the cooling fan in a vehicle installation involves capturing complex fluid dynamic interaction between rotating blades and stationary objects in the vicinity of the fan. This interaction is a function of fan rotation rate, fan blade profile, upstream and downstream installation components. The flow is usually highly turbulent and small geometry details, like the distance between the blade tip and the fan shroud, have strong impact on the fan performance characteristics.
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