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Technical Paper

Comparison of Long-Chain Alcohol Blends, HVO and Diesel on Spray Characteristics, Ignition and Soot Formation

2019-01-15
2019-01-0018
Spray characteristics of fossil Diesel fuel, hydrotreated vegetable oil (HVO) and two oxygenated fuel blends were studied to elucidate the combustion process. The fuels were studied in an optically accessible high-pressure/high-temperature chamber under non-combusting (623 K, 4.69 MPa) and combusting (823 K, 6.04 MPa) conditions. The fuel blends contained the long-chain alcohol 2-ethylhexanol (EH), HVO and either 20 vol.% Diesel or 7 vol.% rapeseed methyl ester (RME) and were designed to have a Diesel-like cetane number (CN). Injection pressures were set to 120 MPa and 180 MPa and the gas density was held constant at 26 kg/m3. Under non-combusting conditions, shadow imaging revealed the penetration length of the liquid and vapor phase of the spray. Under combusting conditions, the lift-off length and soot volume fraction were measured by simultaneously recording time-resolved two-dimensional laser extinction, flame luminosity and OH* chemiluminescence images.
Technical Paper

Spray Characterization of Gasoline Direct Injection Sprays Under Fuel Injection Pressures up to 150 MPa with Different Nozzle Geometries

2019-01-15
2019-01-0063
Maximum fuel injection pressures for GDI engines is expected to increase due to positive effects on emissions and engine-efficiency. Current GDI injectors have maximum operating pressures of 35 MPa, but higher injection pressures have yielded promising reductions in particle number (PN) and improved combustion stability. However, the mechanisms responsible for these effects are poorly understood, and there have been few studies on fuel sprays formed at high injection pressures. This paper summarizes experimental studies on the properties of sprays formed at high injection pressures. The results of these experiments can be used as inputs for CFD simulations and studies on combustion behavior, emissions formation, and combustion system design. The experiments were conducted using an injection rate meter and optical methods in a constant volume spray chamber. Injection rate measurements were performed to determine the injectors’ flow characteristics.
Technical Paper

OH Radical and Soot Concentration Structures in Diesel Sprays under Low Sooting and Non-Sooting Conditions

2018-09-10
2018-01-1690
In an optically accessible high-pressure/high-temperature (HP/HT) chamber, OH radicals, soot concentration, and OH* chemiluminescence images were captured simultaneously at a constant ambient temperature of 823 K and a gas density of 20 kg/m3, with injection pressures of 800-2000 bar using an injector with nozzle orifice having a diameter of 0.1 mm. Swedish market sold MK1 diesel fuel was used in this study. The optical diagnostic methods used were the two-dimensional laser extinction for the soot concentration measurement, planar laser induced fluorescence for the OH radical measurement, OH* chemiluminescence imaging, and the natural flame luminosity imaging. The objective of this study is to explore the diesel spray structures under the low sooting and non-sooting conditions. In this study, it was found that the OH radical zone in the jet’s upstream region expanded to the jet center and the soot concentration decreased when the fuel injection pressure increased.
Technical Paper

Investigation of Interior Noise from Generic Side- View Mirror Using Incompressible and Compressible Solvers of DES and LES

2018-04-03
2018-01-0735
Exterior turbulent flow is an important source of automobile cabin interior noise. The turbulent flow impacts the windows of the cabins to excite the structural vibration that emits the interior noise. Meanwhile, the exterior noise generated from the turbulent flow can also cause the window vibration and generate the interior noise. Side-view mirrors mounted upstream of the windows are one of the predominant body parts inducing the turbulent flow. In this paper, we investigate the interior noise caused by a generic side-view mirror. The interior noise propagates in a cuboid cavity with a rectangular glass window. The exterior flow and the exterior noise are computed using advanced CFD methods: compressible large eddy simulation, compressible detached eddy simulation (DES), incompressible DES, and incompressible DES coupled with an acoustic wave model. The last method is used to simulate the hydrodynamic and acoustic pressure separately.
Technical Paper

Simplifications Applied to Simulation of Turbulence Induced by a Side View Mirror of a Full-Scale Truck Using DES

2018-04-03
2018-01-0708
In this paper, the turbulent flow induced by a production side-view mirror assembled on a full-scale production truck is simulated using a compressible k-ω SST detached eddy simulation (DES) approach -- the improved delayed DES (IDDES). The truck configuration consists of a compartment and a trailer. Due to the large size and geometric complexity of the configuration, some simplifications are applied to the simulation. A purpose of this work is to investigate whether the simplifications are suitable to obtain the reasonable properties of the flow near the side-view mirror. Another objective is to study the aerodynamic performances of the mirror. The configuration is simplified regarding two treatments. The first treatment is to retain the key exterior components of the truck body while removing the small gaps and structures. Furthermore, the trailer is shaped in an apex-truncated square pyramid.
Journal Article

Effects of Nozzle Geometry on the Characteristics of an Evaporating Diesel Spray

2016-10-17
2016-01-2197
The effects of nozzle geometry on diesel spray characteristics were studied in a spray chamber under evaporating conditions using three single-hole nozzles, one cylindrical and two convergent, designated N1 (outlet diameter 140 μm, k-factor 0), N2 (outlet diameter 140 μm, k-factor 2) and N3 (outlet diameter 136 μm, k-factor 2). Spray experiments were performed with each nozzle at two constant gas densities (15 and 30 kg/m3) and an ambient temperature (673 K) at which evaporation occurs, with injection pressures ranging from 800 to 1600 bar. A light absorption and scattering method using visible and UV light was implemented, and shadow images of liquid and vapor phase fuel were recorded with high-speed video cameras. The cylindrical nozzle N1 yielded larger local vapor cone angles than the convergent nozzles N2 and N3 at both gas densities, and the difference became larger as the injection pressure increased.
Technical Paper

Surface Flow Visualization on a Full-Scale Passenger Car with Quantitative Tuft Image Processing

2016-04-05
2016-01-1582
Flow visualization techniques are widely used in aerodynamics to investigate the surface trace pattern. In this experimental investigation, the surface flow pattern over the rear end of a full-scale passenger car is studied using tufts. The movement of the tufts is recorded with a DSLR still camera, which continuously takes pictures. A novel and efficient tuft image processing algorithm has been developed to extract the tuft orientations in each image. This allows the extraction of the mean tuft angle and other such statistics. From the extracted tuft angles, streamline plots are created to identify points of interest, such as saddle points as well as separation and reattachment lines. Furthermore, the information about the tuft orientation in each time step allows studying steady and unsteady flow phenomena. Hence, the tuft image processing algorithm provides more detailed information about the surface flow than the traditional tuft method.
Technical Paper

A 1D Method for Transient Simulations of Cooling Systems with Non-Uniform Temperature and Flow Boundaries Extracted from a 3D CFD Solution

2015-04-14
2015-01-0337
The current work investigates a method in 1D modeling of cooling systems including discretized cooling package with non-uniform boundary conditions. In a stacked cooling package the heat transfer through each heat exchanger depends on the mass flows and temperature fields. These are a result of complex three-dimensional phenomena, which take place in the under-hood and are highly non-uniform. A typical approach in 1D simulations is to assume these to be uniform, which reduces the authenticity of the simulation and calls for additional calibrations, normally done with input from test measurements. The presented work employs 3D CFD simulations of complete vehicle in STAR-CCM+ to perform a comprehensive study of mass-flow and thermal distribution over the inlet of the cooling package of a Volvo FM commercial vehicle in several steady-state operating points.
Journal Article

Structures of Flow Separation on a Passenger Car

2015-04-14
2015-01-1529
The phenomenon of three-dimensional flow separation is and has been in the focus of many researchers. An improved understanding of the physics and the driving forces is desired to be able to improve numerical simulations and to minimize aerodynamic drag over bluff bodies. To investigate the sources of separation one wants to understand what happens at the surface when the flow starts to detach and the upwelling of the streamlines becomes strong. This observation of a flow leaving the surface could be captured by investigating the limiting streamlines and surface parameters as pressure, vorticity or the shear stress. In this paper, numerical methods are used to investigate the surface pressure and flow patterns on a sedan passenger vehicle. Observed limiting streamlines are compared to the pressure distribution and their correlation is shown. For this investigation the region behind the antenna and behind the wheel arch, are pointed out and studied in detail.
Technical Paper

Effect of Rear-End Extensions on the Aerodynamic Forces of an SUV

2014-04-01
2014-01-0602
Under a global impulse for less man-made emissions, the automotive manufacturers search for innovative methods to reduce the fuel consumption and hence the CO2-emissions. Aerodynamics has great potential to aid the emission reduction since aerodynamic drag is an important parameter in the overall driving resistance force. As vehicles are considered bluff bodies, the main drag source is pressure drag, caused by the difference between front and rear pressure. Therefore increasing the base pressure is a key parameter to reduce the aerodynamic drag. From previous research on small-scale and full-scale vehicles, rear-end extensions are known to have a positive effect on the base pressure, enhancing pressure recovery and reducing the wake area. This paper investigates the effect of several parameters of these extensions on the forces, on the surface pressures of an SUV in the Volvo Cars Aerodynamic Wind Tunnel and compares them with numerical results.
Technical Paper

Analysis of Transient Compressible Gas Jets Using High Speed Schlieren Imaging

2013-04-08
2013-01-0871
Transient compressible gas jets, as encountered in direct injection gas fuel engines, have been examined using Schlieren visualization. Helium has been injected into air in a pressure chamber to create the jets examined. The structure of the jets is studied from the mean and coefficient of variation of the penetration length, jet width and jet angle. The quantities are calculated by digital image processing of Schlieren images captured with a high-speed camera. Injection pressure and chamber pressure have been varied to determine whether they have an effect on the response variables. Design of experiments methods have been used to develop the scheme employed in performing the experiments. The mean normalized penetration length of the jets is found to scale with injection to chamber pressure ratio and is in agreement with a momentum conserving relation given in the literature. The dispersion of the penetration length has been found to be in agreement with a normal distribution.
Journal Article

Investigation of the Influence of Tyre Geometry on the Aerodynamics of Passenger Cars

2013-04-08
2013-01-0955
It is well known that wheels are responsible for a significant amount of the total aerodynamic drag of passenger vehicles. Tyres, and mostly rims, have been the subject of research in the automotive industry for the past years, but their effect and interaction with each other and with the car exterior is still not completely understood. This paper focuses on the use of CFD to study the effects of tyre geometry (tyre profile and tyre tread) on road vehicle aerodynamics. Whenever possible, results of the numerical computations are compared with experiments. More than sixty configurations were simulated. These simulations combined different tyre profiles, treads, rim designs and spoke orientation on two car types: a sedan and a sports wagon. Two tyre geometries were obtained directly from the tyre manufacturer, while a third geometry was obtained from our database and represents a generic tyre which covers different profiles of a given tyre size.
Technical Paper

Modelling of Gasoline and Ethanol Hollow-Cone Sprays Using OpenFOAM

2011-08-30
2011-01-1896
Over the past few years, an open-source code called OpenFOAM has been becoming a promising CFD tool for multi-dimensional numerical simulations of internal combustion engines. The primary goal of the present study is to assess the feasibility of the code for computations of hollow-cone sprays discharged by an outward-opening pintle-type injector by simulating the experiments performed recently by Hemdal et al., (SAE 2009-01-1496) with gasoline and ethanol sprays under the following conditions: air temperature Tair = 295 or 350 K, air pressure pair = 6 bar, fuel temperature Tfuel = 243, or 295, or 320 K, and fuel injection pressure pinj = 50, or 125, or 200 bar. To simulate the experiments, a pintle injector model and the physical properties of gasoline were implemented in OpenFOAM. The flow field calculated using the pintle injector model is more realistic than that yielded by the default unit injector model normally used in OpenFOAM.
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

Reducing Pressure Fluctuations at High Loads by Means of Charge Stratification in HCCI Combustion with Negative Valve Overlap

2009-06-15
2009-01-1785
Future demands for improvements in the fuel economy of gasoline passenger car engines will require the development and implementation of advanced combustion strategies, to replace, or combine with the conventional spark ignition strategy. One possible strategy is homogeneous charge compression ignition (HCCI) achieved using negative valve overlap (NVO). However, several issues need to be addressed before this combustion strategy can be fully implemented in a production vehicle, one being to increase the upper load limit. One constraint at high loads is the combustion becoming too rapid, leading to excessive pressure-rise rates and large pressure fluctuations (ringing), causing noise. In this work, efforts were made to reduce these pressure fluctuations by using a late injection during the later part of the compression. A more appropriate acronym than HCCI for such combustion is SCCI (Stratified Charge Compression Ignition).
Technical Paper

A Study on Head Injury Risk in Car-to-Pedestrian Collisions Using FE-Model

2009-06-09
2009-01-2263
Head injury is quite frequently occurred in car-to-pedestrian collisions, which often places an enormous burden to victims and society. To address head protection and understand the head injury mechanisms, in-depth accident investigation and accident reconstructions were conducted. A total of 6 passenger-cars to adult-pedestrian accidents were sampled from the in-depth accident investigation in Changsha China. Accidents were firstly reconstructed by using Multi-bodies (MBS) pedestrian and car models. The head impact conditions such as head impact velocity; position and orientation were calculated from MBS reconstructions, which were then employed to set the initial conditions in the simulation of a head model striking a windshield using Finite Element (FE) head and windshield models. The intracranial pressure and stress distribution of the FE head model were calculated and correlated with the injury outcomes.
Technical Paper

An Experimental Investigation of Spray-Wall Interaction of Diesel Sprays

2009-04-20
2009-01-0842
Wall wetting can occur irrespective of combustion concept in diesel engines, e.g. during the compression stroke. This action has been related to engine-out emissions in different ways, and an experimental investigation of impinging diesel sprays is thus made for a standard diesel fuel and a two-component model fuel (IDEA). The experiment was performed at conditions corresponding to those found during the compression stroke in a heavy duty diesel engine. The spray characteristics of two fuels were measured using two different optical methods: a Phase Doppler Particle Analyzer (PDPA) and high-speed imaging. A temperature controlled wall equipped with rapid, coaxial thermocouples was used to record the change in surface temperature from the heat transfer of the impinging sprays.
Technical Paper

The Role of Aerodynamics in the 1955 Le Mans Crash

2008-12-02
2008-01-2996
In the 1955 Le Mans race the worst crash in motor racing history occurred and this accident would change the face of motor racing for decades. After the crash numerous investigations on the disaster were performed, and fifty years after some interesting books were launched on the subject. However, a number of key questions remain unsolved; and one open area is the influence of aerodynamics on the scenario, since the Mercedes-Benz 300 SLR involved in the crash was equipped with an air-brake and its influence on the accident is basically unknown. This work may be considered as a first attempt to establish CFD as a tool to aid in resolving aerodynamic aspects in motor sport accidents and in the present paper, CFD has been used to investigate the aerodynamics and estimate the drag and lift coefficients of the Mercedes-Benz 300 SLR used in the Le Mans race of 1955.
Technical Paper

Soot Evolution in Multiple Injection Diesel Flames

2008-10-06
2008-01-2470
In order to meet future emission regulations, various new combustion concepts are being developed, several of which incorporate advanced diesel injection strategies, e.g. multiple injections, offering attractive potential benefits. In this study the effects of split injections on soot evolution in diesel flames were investigated in a series of flame experiments performed using a high pressure, high temperature (HP/HT) spray chamber and laser-induced incandescence apparatus to measure soot volume fractions. The focus was on split injections with varied dwell times preceded by a short pilot. The results, which were analyzed and compared to results from engine tests, show that net soot production can be decreased by applying an appropriate split injection strategy.
Technical Paper

Ion Current Sensing in an Optical HCCI Engine with Negative Valve Overlap

2007-01-23
2007-01-0009
Ion current sensors have high potential utility for obtaining feedback signals directly from the combustion chamber in internal combustion engines. This paper describes experiments performed in a single-cylinder optical engine operated in HCCI mode with negative valve overlap to explore this potential. A high-speed CCD camera was used to visualize the combustion progress in the cylinder, and the photographs obtained were compared with the ion current signals. The optical data indicate that the ions responsible for the chemiluminescence from the HCCI combustion have to be in contact with the sensing electrode for an ion current to start flowing through the measurement circuit. This also means that there will be an offset between the time at which 50% of the fuel mass has burned and 50% of the ion current peak value is reached, which is readily explained by the results presented in the paper.
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