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Technical Paper

Comparative Study to Assess the Soot Reduction Potential of Different In-Cylinder Methods and Exhaust Gas Aftertreatment Systems for Direct Injection Diesel Engines

In this study different methods to reduce the soot emissions of Diesel engines were investigated and compared to obtain their soot reduction potential. Apart from investigations on the practically usable engine map area with so called homogeneous charge compression ignition (HCCI) combustion processes a new heterogeneous combustion processes was developed and investigated which offers significantly reduced soot emissions while still applicable in the entire engine map. For the HCCI experiments the emphasis was put on the achievable engine load range when using conventional injector nozzles which still allow a conventional heterogeneous engine operation.
Technical Paper

67 Analysis of Mixture Conditions in a Small Two Stroke Engine Using a Gas Sampling Valve

The quality of mixture formation and the combustion process is of significant importance for reducing the hydrocarbon emissions of small two stroke engines. The scope of this work was to investigate the mixture conditions after the exhaust closes and after the end of combustion depending on various engine operating points. For this experimental investigation a Gas Sampling Valve (GSV) was combined with a flame ionisation detector (FID) and a CO2-analyser. Using this technique, it was possible to measure the hydrocarbon concentration after end of combustion. Furthermore the local residual gas concentration after exhaust closes was determined. To allow for a comparison of the experimental results with calculations with CFD codes, in cylinder pressure measurement and exhaust gas measurements are done additionally.
Technical Paper

An Experimental Study of Homogeneous Charge Compression Ignition (HCCI) with Various Compression Ratios, Intake Air Temperatures and Fuels with Port and Direct Fuel Injection

A promising approach for reducing both NOx- and particulate matter emissions with low fuel consumption is the so called homogeneous charge compression ignition (HCCI) combustion process. Single-cylinder engine tests were carried out to assess the influence of several parameters on the HCCI combustion. The experiments were performed both with port fuel injection (PFI) and with direct injection (DI) under various compression ratios, intake air temperatures and EGR-rates. Special emphasis was put on the fuel composition by using different gasoline and diesel fuels as well as n-heptane. Besides engine out emissions (CO2, CO, NO, O2, HC, soot) and in-cylinder pressure indication for burning process analysis, the combustion itself was visualised using an optical probe.
Technical Paper

A New Approach for Three-Dimensional High-Speed Combustion Diagnostics in Internal Combustion Engines

This paper introduces a new measuring and analyzing method for the investigation of the spatial flame propagation in IC engines. Three optical high-speed measuring devices are connected and synchronized in order to detect the flame radiation from different perspectives via fiberoptical endoscopes. The resulting two-dimensional images provide a starting basis for the subsequent reconstruction of the three-dimensional flame geometry. The reconstruction is carried out by a newly developed software tool. The capability of the new methodology has been proven in a first test series. A one-cylinder SI engine with direct-injection is operated in both homogeneous and spray-guided stratified injection mode. Intake flow conditions and air/fuel ratio are varied in order to investigate the effects on flame spread. The volumetric flame developments are analyzed as well as the location of the combustion center in absolute coordinates.
Technical Paper

Application of Multifiber Optics in Handheld Power Tools with High Speed Two-Stroke Gasoline Engines

When developing effective exhaust emission reduction measures, a better understanding of the complex working cycle in crankcase scavenged two-stroke gasoline engines. However, in a two-stroke gasoline engine detailed measurement and analysis of combustion data requires significantly more effort, when compared to a lower speed four-stroke engine. Particularly demanding are the requirements regarding the high speed (>10,000 rpm) which inevitably goes along with heavy vibrations and high temperatures of the air cooled cylinders. Another major challenge to the measuring equipment is the increased cleaning demand of the optical sensor surface due to the two-stroke gasoline mixture. In addition, the measuring equipment has to be adapted to the small size engines. Therefore, only a fiber optical approach can deliver insight into the cylinder for analyzing the combustion performance.
Technical Paper

Application of Particle Image Velocimetry for Investigation of Spray Characteristics of an Outward Opening Nozzle for Gasoline Direct Injection

The hollow cone spray from a high pressure outward opening nozzle was investigated inside a pressure vessel by means of particle image velocimetry (PIV). The flow velocities of the air outside the spray were measured via PIV in combination with fluorescent seeding particles and optical filters. The high pressure piezo electric injector has an annular nozzle to provide a hollow cone spray with an angle of about 90°. During injection a very strong and stable vortex structure is induced by the fuel spray. Besides the general spray/air interaction, the investigation of double and triple fuel injections was the main focus of this study.
Technical Paper

Investigations on Soot Emission Behavior of A Common-Rail Diesel Engine during Steady and Non-Steady Operating Conditions by Means of Several Measuring Techniques

In this work the influence of various engine load changes with different engine speeds on the soot particle concentrations and properties was investigated because these operating modes are well known for short but high soot emissions. To derive specific information on emission behavior of particle matters tests were carried out with the Two-Color-Method and the so called RAYLIX technique in a four-cylinder CR-Diesel engine. The Two-Color-Method (2CM) gives crank angle resolved information about soot formation and oxidation processes inside the combustion chamber of a single cylinder. The RAYLIX technique is a combination of Rayleigh-scattering, Laser-Induced-Incandescence (LII) and extinction measurements which enable simultaneous measurements of temporally and spatially resolved soot concentration, mean primary particle radii and number densities in the exhaust gas manifold of the same cylinder investigated by the Two-Color-Method.
Technical Paper

A New Flame Jet Concept to Improve the Inflammation of Lean Burn Mixtures in SI Engines

Engines with gasoline direct injection promise an increase in efficiency mainly due to the overall lean mixture and reduced pumping losses at part load. But the near stoichiometric combustion of the stratified mixture with high combustion temperature leads to high NOx emissions. The need for expensive lean NOx catalysts in combination with complex operation strategies may reduce the advantages in efficiency significantly. The Bowl-Prechamber-Ignition (BPI) concept with flame jet ignition was developed to ignite premixed lean mixtures in DISI engines. The mainly homogeneous lean mixture leads to low combustion temperatures and subsequently to low NOx emissions. By additional EGR a further reduction of the combustion temperature is achievable. The BPI concept is realized by a prechamber spark plug and a piston bowl. The main feature of the concept is its dual injection strategy.
Technical Paper

Use of Ceramic Components in Sliding Systems for High-Pressure Gasoline Fuel Injection Pumps

Spray-guided gasoline direct injection demonstrates great potential to reduce both fuel consumption and pollutant emissions. However, conventional materials used in high-pressure pumps wear severely under fuel injection pressures above 20 MPa as the lubricity and viscosity of gasoline are very low. The use of ceramic components promises to overcome these difficulties and to exploit the full benefits of spray-guided GDI-engines. As part of the Collaborative Research Centre “High performance sliding and friction systems based on advanced ceramics” at Karlsruhe Institute of Technology, a single-piston high-pressure gasoline pump operating at up to 50 MPa has been designed. It consists of 2 fuel-lubricated sliding systems (piston/cylinder and cam/sliding shoe) that are built with ceramic parts. The pump is equipped with force, pressure and temperature sensors in order to assess the behaviour of several material pairs.
Technical Paper

Investigations of Mixture Formation and Combustion in Gasoline Direct Injection Engines

The spray propagation and disintegration is investigated in a pressure chamber. With Particle Image Velocimetry the direction and velocity of both, fuel droplets and induced gas flow are detected. By means of shadow photographs the spray cone geometry is visualized. To verify the predictions made of the measurements mentioned above and to rate the quality of the tuning of the parameters in-cylinder gas flow, injection pressure, position of Injector and position of spark plug under real engine conditions, a fast gas sampling valve is used in three different engines. The in-cylinder gas temperature and the soot concentration are measured crank angle resolved by means of the Two-Colour-Method in a 1-cylinder GDI-engine. The soot concentration and temperature show the influence of the injection pressure on emissions like soot and nitric oxide.
Technical Paper

Potential of Reducing the NOX Emissions in a Spray Guided DI Gasoline Engine by Stratified Exhaust Gas Recirculation (EGR)

In this paper, results of experimental and numerical investigations of stratified exhaust gas recirculation in a single-cylinder gasoline engine are presented. The engine was operated in spray guided direct injection mode. The radial exhaust gas stratification was achieved by a spatial and temporal separated intake of exhaust gas and fresh air. The spatial separation of both fluids was realized by specially shaped baffles in the inlet ports, which prevent an early mixing up to the inlet valves. The temporally separation was performed by impulse charge valves, with one for the fresh air and one for the exhaust gas. From various possible strategies for time-dependent intake of fresh air and exhaust gas, four different strategies for the exhaust gas stratification were examined.
Technical Paper

Investigations of Ignition Processes Using High Frequency Ignition

High frequency ignition (HFI) and conventional transistor coil ignition (TCI) were investigated with an optically accessible single-cylinder research engine to gain fundamental understanding of the chemical reactions taking place prior to the onset of combustion. Instead of generating heat in the gap of a conventional spark plug, a high frequency / high voltage electric field is employed in HFI to form chemical radicals. It is generated using a resonant circuit and sharp metallic tips placed in the combustion chamber. The setup is optimized to cause a so-called corona discharge in which highly energized channels (streamers) are created while avoiding a spark discharge. At a certain energy the number of ionized hydrocarbon molecules becomes sufficient to initiate self-sustained combustion. HFI enables engine operation with highly diluted (by air or EGR) gasoline-air mixtures or at high boost levels due to the lower voltage required.
Technical Paper

Influence of the Alcohol Type and Concentration in Alcohol-Blended Fuels on the Combustion and Emission of Small Two-Stroke SI Engines

The combustion processes optimization is one of the most important factors to enhancing thermal efficiency and reducing exhaust emissions of combustion engines [1; 2]. Future emission regulations for small two-stroke SI engines require that the emissions of gases causing the greenhouse effect, such as carbon dioxide, to be reduced. One possible way to reduce exhaust gas emissions from two-stroke small off-road engines (SORE) is to use biogenic fuels. Because of their nearly closed carbon dioxide circuit, the emissions of carbon dioxide decrease compared to the use of fossil fuels. Also biogenic fuels have a significant influence on the combustion process and thus the emissions of different exhaust gas components may be reduced. Besides greenhouse gases, several other exhaust gas components need to be reduced because of their toxicity to the human health. For example, aromatic hydrocarbons cause dangerous health problems, and can be reduced by using alkylate fuel.
Technical Paper

Comparison of the Emission Behaviour and Fuel Consumption of a Small Two-Stroke SI Chainsaw under Test-Bed- and Real In-Use Conditions

The emission behaviour of an internal combustion engine under test-bed conditions shows differences to the emission behaviour under real in-use conditions. Because of this fact, the developers of combustion engines and the legislator are focussing on the measurement and optimization of real in-use emissions. To this day, the research, the adjustment of the carburettor and the legislation of small handheld engines is performed under test bench conditions, especially conditioned fuel pressure and temperature, as well as air temperature. Also the engines are laid out for two operation points: rated speed with full open throttle and idle speed. This test-procedure is used for all kinds of handheld off-road applications and does not consider the load profile of the different power tools. Especially applications with transient load profiles, for example chainsaws, work in more than two operating points in real use.
Technical Paper

Temperature Measurement and NO Determination in SI Engines Using Optical Fiber Sensors

This paper presents a special optical fiber technique which allows to measure temperatures in SI engines using the emission bands or respectively emission lines of the temperature radiation of diatomic molecules. The measurement technique enables the detection of average temperature in a small volume element. These temperatures are used to determine the local NO concentrations using the extended Zeldovich-mechanism. First, theoretical background of both temperature and NO-determination and measurement technique including optical fiber sensors are described. Finally, the temperature and NO dependence versus crank angle are presented and discussed at different combustion chamber locations for different engine operating conditions.
Technical Paper

Investigation of the Bowl-Prechamber-Ignition (BPI) Concept in a Direct Injection Gasoline Engine at Part Load

In this work a new concept for GDI engines is presented. Concerning a stable ignition a main goal of the so called Bowl-Pre-chamber-Ignition (BPI) process is to reduce the influence of varying flow and spray effects. The characteristic signs of the concept are the dual direct injection, a centrally arranged piston bowl and the special pre-chamber spark plug, that partly dips into the bowl at TDC. During that process most fuel is injected early (intake stroke) into the intake manifold or directly into the cylinder to form a homogeneous pre-mixture. Later in the compression stroke, only a small amount of fuel is injected into the piston bowl. So formed locally stratified charge mixture is transported by the piston bowl to the pre-chamber-spark plug, the pre-chamber dips into the bowl and the mixture flows directly to the spark plug electrode. The result is a very stable lean combustion.
Technical Paper

Influence of Mixture Preparation on Combustion and Emissions Inside an SI Engine by Means of Visualization, PIV and IR Thermography During Cold Operating Conditions

The focus of this work was to determine the influence of spray targeting on temperature distributions, combustion progress and unburned hydrocarbon (HC) emissions at cold operating conditions, and to show the capability of model and full engine tests adapted for different measurement techniques. A comprehensive study applying endoscopic visualization, infrared thermography, combustion and emission measurements was carried out in a 4-stroke 4-cylinder 16-valve production engine with intake port injection during different engine operating conditions including injection angle and timing. In addition 2D visualization and PIV measurements were performed in a back-to-back model test section with good optical access to the intake manifold and the combustion chamber. The measurements in both set ups were in good agreement and show that model tests could lead to useful findings for a real engine.
Journal Article

High Pressure Gasoline Direct Injection in Spark Ignition Engines - Efficiency Optimization through Detailed Process Analyses

At part load and wide open throttle operation with stratified charge and lean mixture conditions the Direct Injection Spark Ignition (DISI) engine offers similar efficiency levels compared to compression ignition engines The present paper reports on results of recent studies on the impact of the in-cylinder processes in DISI engines e. g. the injection, the in-cylinder flow, the mixture preparation and the ignition on the combustion, the energy conversion and the exhaust emission behavior. The analyses of the spray behavior, of the in-cylinder flow during compression as well as of the flame propagation have been carried out applying advanced optical measurement techniques. The results enable a targeted optimization of the combustion process with respect to engine efficiency and exhaust emissions. The benefits of an increase in fuel injection pressures up to 100 MPa are discussed.
Journal Article

Investigations on Pre-Ignition in Highly Supercharged SI Engines

This paper presents the results of a study on reasons for the occurrence of pre-ignition in highly supercharged spark ignition engines. During the study, the phenomena to be taken into account were foremost structured into a decision tree according to their physical working principles. Using this decision tree all conceivable single mechanisms to be considered as reasons for pre-ignition could be derived. In order to judge each of them with respect to their ability to promote pre-ignition in a test engine, experimental investigations as well as numerical simulations were carried out. The interdependence between engine operating conditions and pre-ignition frequency was examined experimentally by varying specific parameters. Additionally, optical measurements using an UV sensitive high-speed camera system were performed to obtain information about the spatial distribution of pre-ignition origins and their progress.
Journal Article

Experimental Investigations of a DISI Engine in Transient Operation with Regard to Particle and Gaseous Engine-out Emissions

The investigation of transient engine operation plays a key role of the future challenges for individual mobility in terms of real driving emissions (RDE). A fundamental investigation of the transient engine operation requires the simultaneous application of measurement technologies for an integrated study of mixture formation, combustion process and emission formation. The major prerequisite is the combustion cycle and crank angle resolved analysis of the process for at least several individual consecutive combustion cycles during transient operation. The investigations are performed with a multi cylinder DISI engine at an Engine-in-the-Loop test bench, able to operate the engine in driving cycles as well as within target profiles (e.g. speed and torque profiles). The research project describes the methodology of analyzing elementary transient operational phases, (e.g. different variants of load steps).