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Technical Paper

Large-Eddy Simulation of the Flow Around a Ground Vehicle Body

2001-03-05
2001-01-0702
Large Eddy Simulation of the the flow around bus-like ground vehicle body is presented. Both the time-averaged and instantaneous aspects of this flow are studied. Time-averaged velocity profiles are computed and compared with the experiments [1] and show good agreement. The separation length and the base pressure coefficient are presented. The predicted pumping process in the near wake occurs with a Strouhal number St = 0.073, compared with St = 0.069 in the experiment. Unsteady results at two points are presented and compared with the experiments. The coherent structures are studied and show good agreement with the experiments.
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

A Study of the Influence of Nozzle Orifice Geometries on Fuel Evaporation using Laser-Induced Exciplex Fluorescence

2003-05-19
2003-01-1836
Projected stringent emissions legislation will make tough demands on engine development. For diesel engines, in which combustion and emissions formation are governed by the spray formation and mixing processes, fuel injection plays a major role in the future development of cleaner engines. It is therefore important to study the fundamental features of the fuel injection process. In an engine the fuel is injected at high pressure into a pressurized and hot environment of air, which causes droplet formation and fuel evaporation. The injected fuel then forms a gaseous phase surrounding the liquid phase. The amount of evaporated fuel in relation to the total amount of injected fuel is of importance for engine performance, i.e. ignition delay and mixing rate. In this paper, the fraction of evaporated fuel was determined for sprays, using different orifice diameters ranging from 0.100 mm up to 0.227 mm, with the aid of a high-pressure spray chamber.
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

High Pressure Ethanol Injection under Diesel-Like Conditions

2017-03-28
2017-01-0857
Laws concerning to emissions from heavy duty (HD) internal combustion engines are becoming increasingly stringent. New engine technologies are therefore needed to satisfy these new legal requirements and reduce fossil fuel dependency. One way to achieve both objectives is to partially replace fossil fuels with alternatives that are more sustainable with respect to emissions of greenhouse gas, particulates and NOx. As a first step towards the development of a direct injected dual fuel engine using diesel fuel and renewable alcohols such as methanol or ethanol, we have studied ethanol (E100) sprays generated with a standard high pressure diesel fuel injection system in a high pressure/temperature spray chamber with optical access. The experiments were performed at a gas density of ∼27kg/m3 at ∼550 °C and ∼60 bar, representing typical operating conditions for a HD engine at low loads.
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

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

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

Effects of Varying Engine Settings on Combustion Parameters, Emissions, Soot and Temperature Distributions in Low Temperature Combustion of Fischer-Tropsch and Swedish Diesel Fuels

2009-11-02
2009-01-2787
It has been previously shown that engine-out soot emissions can be reduced by using Fischer-Tropsch (FT) fuels, due to their lack of aromatics, compared to conventional Diesel fuels. In this investigation the engine-out emissions and fuel consumption parameters of an FT fuel derived from natural gas were compared to those of Swedish low sulfur diesel (MK1) when used in Low Temperature Combustion mode in a single cylinder heavy-duty diesel engine. The effects of varying Needle Opening Pressure (NOP), Charge Air Pressure (CAP) and Exhaust Gas Recirculation (EGR) according to an experimental design on the measured variables were also assessed. CAP and EGR were found to be the most significant factors for the combustion and emission parameters of both fuels. Increases in CAP resulted in lower soot emissions due to enhanced charge mixing, however NOx emissions rose as CAP increased.
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

Injection Strategy Optimization for a Light Duty DI Diesel Engine in Medium Load Conditions with High EGR rates

2009-04-20
2009-01-1441
Further restrictions on NOx emissions and the extension of current driving cycles for passenger car emission regulations to higher load operation in the near future (such as the US06 supplement to the FTP-75 driving cycle) requires attention to low emission combustion concepts in medium to high load regimes. One possibility to reduce NOx emissions is to increase the EGR rate. The combustion temperature-reducing effects of high EGR rates can significantly reduce NO formation, to the point where engine-out NOx emissions approach zero levels. However, engine-out soot emissions typically increase at high EGR levels, due to the reduced soot oxidation rates at reduced combustion temperatures and oxygen concentrations.
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.
Technical Paper

Experimental and Numerical Investigations of the Base Wake on an SUV

2013-04-08
2013-01-0464
With the increase in fuel prices and the increasingly strict environmental legislations regarding CO₂ emissions, reduction of the total energy consumption of our society becomes more important. Passenger vehicles are partly responsible for this consumption due to their strong presence in the daily life of most people. Therefore reducing the impact of cars on the environment can assist in decreasing the overall energy consumption. Even though several fields have an impact on a passenger car's performance, this paper will focus on the aerodynamic part and more specifically, the wake behind a vehicle. By definition a car is a bluff body on which the air resistance is for the most part driven by pressure drag. This is caused by the wake these bodies create. Therefore analyzing the wake characteristics behind a vehicle is crucial if one would like to reduce drag.
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

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

Effect of Ultra-High Injection Pressure on Diesel Ignition and Flame under High-Boost Conditions

2008-06-23
2008-01-1603
In this work, we conducted three-dimensional numerical simulations to investigate the effect of ultra-high injection pressure on diesel ignition and flame under high-boost and medium-load conditions. Three injection cases employed in experiments with a multi-cylinder Volvo D12 engine were applied for validation. The simulations were performed using the KIVA-3V code, with a Kelvin-Helmholz/Rayleigh-Taylor (KH/RT) spray breakup model and a diesel surrogate mechanism involving 83 species and 445 reactions. A range of higher injection pressure levels were projected and the injection rates estimated for the current study. Three different rate shapes of injection were projected and investigated as well. All the projected injection events start at top dead center (TDC). Computations demonstrate that high-pressure injection strongly affects engine ignition and combustion.
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

Investigations of the Rear-End Flow Structures on a Sedan Car

2016-04-05
2016-01-1606
The aerodynamic drag, fuel consumption and hence CO2 emissions, of a road vehicle depend strongly on its flow structures and the pressure drag generated. The rear end flow which is an area of complex three-dimensional flow structures, contributes to the wake development and the overall aerodynamic performance of the vehicle. This paper seeks to provide improved insight into this flow region to better inform future drag reduction strategies. Using experimental and numerical techniques, two vehicle shapes have been studied; a 30% scale model of a Volvo S60 representing a 2003MY vehicle and a full scale 2010MY S60. First the surface topology of the rear end (rear window and trunk deck) of both configurations is analysed, using paint to visualise the skin friction pattern. By means of critical points, the pattern is characterized and changes are identified studying the location and type of the occurring singularities.
Technical Paper

Wake and Unsteady Surface-Pressure Measurements on an SUV with Rear-End Extensions

2015-04-14
2015-01-1545
Previous research on both small-scale and full-scale vehicles shows that base extensions are an effective method to increase the base pressure, enhancing pressure recovery and reducing the wake size. These extensions decrease drag at zero yaw, but show an even larger improvement at small yaw angles. In this paper, rear extensions are investigated on an SUV in the Volvo Cars Aerodynamic Wind Tunnel with focus on the wake flow and on the unsteady behavior of the surface pressures near the base perimeter. To increase the effect of the extensions on the wake flow, the investigated configurations have a closed upper- and lower grille (closed-cooling) and the underbody has been smoothed with additional panels. This paper aims to analyze differences in flow characteristics on the wake of an SUV at 0° and 2.5° yaw, caused by different sets of extensions attached to the base perimeter. Extensions with several lengths are investigated with and without a kick.
Technical Paper

Development of a Computationally Efficient Progress Variable Approach for a Direct Injection Stochastic Reactor Model

2017-03-28
2017-01-0512
A novel 0-D Probability Density Function (PDF) based approach for the modelling of Diesel combustion using tabulated chemistry is presented. The Direct Injection Stochastic Reactor Model (DI-SRM) by Pasternak et al. has been extended with a progress variable based framework allowing the use of a pre-calculated auto-ignition table. Auto-ignition is tabulated through adiabatic constant pressure reactor calculations. The tabulated chemistry based implementation has been assessed against the previously presented DI-SRM version by Pasternak et al. where chemical reactions are solved online. The chemical mechanism used in this work for both, online chemistry run and table generation, is an extended version of the scheme presented by Nawdial et al. The main fuel species are n-decane, α-methylnaphthalene and methyl-decanoate giving a size of 463 species and 7600 reactions.
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