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Technical Paper

A Four Stroke Camless Engine, Operated in Homogeneous Charge Compression Ignition Mode with Commercial Gasoline

2001-09-24
2001-01-3610
A single cylinder, naturally aspirated, four-stroke and camless (Otto) engine was operated in homogeneous charge compression ignition (HCCI) mode with commercial gasoline. The valve timing could be adjusted during engine operation, which made it possible to optimize the HCCI engine operation for different speed and load points in the part-load regime of a 5-cylinder 2.4 liter engine. Several tests were made with differing combinations of speed and load conditions, while varying the valve timing and the inlet manifold air pressure. Starting with conventional SI combustion, the negative valve overlap was increased until HCCI combustion was obtained. Then the influences of the equivalence ratio and the exhaust valve opening were investigated. With the engine operating on HCCI combustion, unthrottled and without preheating, the exhaust valve opening, the exhaust valve closing and the intake valve closing were optimized next.
Technical Paper

A Simple Model of Unsteady Turbulent Flame Propagation

1997-10-01
972993
A model of premixed turbulent combustion is modified for multi-dimensional computations of SI engines. This approach is based on the use of turbulent flame speed in order to suggest a closed balance equation for the mean combustion progress variable. The model includes a single unknown input parameter to be tuned. This model is tested against two sets of experimental data obtained by Bradley et al [17, 18 and 19] and Karpov and Severin [15] in fan-stirred bombs. The model quantitatively predicts the development of the turbulent flame speed, the effects of the initial pressure, temperature, and mixture composition on the turbulent flame speed, and the effects of r.m.s. turbulent velocity and burning mixture composition on the rate of the pressure rise. These results were computed with the same value of the aforementioned unknown input parameter of the model.
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

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.
Journal Article

An Evaluation of Different Combustion Strategies for SI Engines in a Multi-Mode Combustion Engine

2008-04-14
2008-01-0426
Future pressures to reduce the fuel consumption of passenger cars may require the exploitation of alternative combustion strategies for gasoline engines to replace, or use in combination with the conventional stoichiometric spark ignition (SSI) strategy. Possible options include homogeneous lean charge spark ignition (HLCSI), stratified charge spark ignition (SCSI) and homogeneous charge compression ignition (HCCI), all of which are intended to reduce pumping and thermal losses. In the work presented here four different combustion strategies were evaluated using the same engine: SSI, HLCSI, SCSI and HCCI. HLCSI was achieved by early injection and operating the engine lean, close to its stability limits. SCSI was achieved using the spray-guided technique with a centrally placed multi-hole injector and spark-plug. HCCI was achieved using a negative valve overlap to trap hot residuals and thus generate auto-ignition temperatures at the end of the compression stroke.
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

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

CFD Modelling of Gasoline Sprays

2005-09-11
2005-24-086
A comprehensive model for sprays emerging from high pressure swirl injectors for GDI engine application has been developed. The primary and secondary atomization mechanism as well as the evaporation process both in standard and superheated conditions are taken into account. The spray modelling after the injection is based on the Liquid Instability Sheet Atomization (LISA) approach, modified to correctly predict the liquid sheet thickness at the breakup length. The effect of different values of the superheat degree on evaporation and impact on the spray distribution and fuel-air mixing is analyzed. Comparisons with experimental data show good agreements under atmospheric conditions and with different superheated degrees, while some discrepancies occur under higher ambient pressures.
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

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

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.
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

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.
Journal Article

Effects of High Injection Pressure, EGR and Charge Air Pressure on Combustion and Emissions in an HD Single Cylinder Diesel Engine

2009-11-02
2009-01-2815
When increasing EGR from low levels to a level that corresponds to low temperature combustion, soot emissions initially increase due to lower soot oxidation before decreasing to almost zero due to very low soot formation. At the EGR level where soot emissions start to increase, the NOx emissions are low, but not sufficiently low to comply with future emission standards and at the EGR level where low temperature combustion occurs CO and HC emissions are too high. The purpose of this study was to investigate the possibilities for shifting the so-called soot bump (where soot levels are increased) to higher EGR levels, or to reduce the magnitude of the soot bump using very high injection pressures (up to 240 MPa) while reducing the NOx emissions using EGR. The possibility of reducing the CO and HC emissions at high EGR levels due to the increased mixing caused by higher injection pressure was also investigated and the flame was visualized using an endoscope at chosen EGR values.
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

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.
Journal Article

Estimation of Cylinder-Wise Combustion Features from Engine Speed and Cylinder Pressure

2008-04-14
2008-01-0290
Advanced engine control and diagnosis strategies for internal combustion engines need accurate feedback information from the combustion engine. The feedback information can be utilized to control combustion features which allow the improvement of engine's efficiency through real-time control and diagnosis of the combustion process. This article describes a new method for combustion phase and IMEP estimation using one in-cylinder pressure and engine speed. In order to take torsional deflections of the crankshaft into account a gray-box model of the crankshaft is identified by subspace identification. The modeling accuracy is compared to a stiff physical crankshaft model. For combustion feature estimation, the identified MISO (multiple input single output) system is inverted. Experiments for a four-cylinder spark-ignition engine show the superior performance of the new method for combustion feature estimation compared to a stiff model approach.
Technical Paper

Experimental Investigation of the Effect of Needle Opening (NOP) Pressure on Combustion and Emissions Formation in a Heavy Duty DI Diesel Engine

2004-10-25
2004-01-2921
This paper presents an investigation of the effects of varying needle opening pressure (NOP) (375 to 1750 bar), engine speed (1000 rpm to 1800 rpm), and exhaust gas recirculation (EGR) (0% to 20 %) on the combustion process, exhaust emissions, and fuel consumption at low (25 %) and medium (50 %) loads in a single cylinder heavy duty DI diesel research engine with a displacement of 2.02 l. The engine was equipped with an advanced two-actuator E3 Electronic Unit Injector (EUI) from Delphi Diesel, with a maximum injection pressure of 2000 bar. In previous versions of the EUI system, the peak injection pressure was a function of the injection duration, cam lift, and cam rate. The advanced EUI system allows electronic control of the needle opening and closing. This facilitates the generation of high injection pressures, independently of load and speed.
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

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.
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