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In gasoline direct injection engines with stratified-combustion strategies only a short time is available for mixture preparation. Therefore, investigations are carried out to evaluate the influence of high injection pressure up to 50 MPa in order to optimize the mixture preparation. Two types of multi-hole injectors are analyzed in a pressure vessel under various pressure and temperature conditions. Laser light sheet visualization technique is applied in order to determine spray characteristics like shape, angle, penetration depth and spray width. To determine the velocity of the air surrounding the spray, a PIV (Particle Image Velocimetry) measurement technique is used. Droplet sizes and velocities are measured with a Phase Doppler Anemometer (PDA) in different positions in the spray center and at the spray edge. Spray visualization experiments show the influence of evaporation on spray propagation at higher temperatures.

Combustion zone (flame) propagation and flow velocities are measured using optical measurement techniques in a single-cylinder direct injected diesel engine. Combustion and, hence, flame propagation is detected by optical fibers and flow velocities have been measured by a new single-color, 2 dimensional Laser Doppler Velocimeter (LDV). Flame propagation and flow velocities could not be measured simultaneously. Consequently, pressure traces which were recorded during each measurement served as a criterion for selecting similar combustion cycles from flame and flow velocity measurements. The operational speed of the engine was 1100 rpm and the power cylinder was configured with a combustion bowl in the piston. For the purpose of the tests, the intake swirl number was either 1.8 or 4.2, the latter corresponding to the application of a shrouded inlet valve. It has been shown that variation of several significant engine parameters influences both combustion and fluid flow history.

The quality of air-/fuel-mixture is of prime importance for cycle fluctuations of combustion. Investigations of mixture formation and conditions in SI engines have been subject of intensive research since many years. The scope of this work was to investigate crank angle resolved determination of qualitative and quantitative mixture conditions inside the combustion chamber in dependence on various engine operating conditions. For this experimental investigation a time resolved Gas Sampling Valve (GSV) was combined with a flame ionisation detector (FID), a CO2-analyzer and a mass spectrometer. The GSV also enables the determination of residual gas concentration. Measurements on a DI gasoline engine show influences of air-/fuel-mixture in dependence on various engine operating conditions when the engine runs in charge stratification mode. Moreover, experimental results of local mixture composi-tion are compared with fuel distribution, calculated from CFD-codes.

The primary objective of this paper is to compare different methods of knock detection based on cylinder pressure data, with special regard to identifying knocking cycles and detecting the onset of knock. These investigations have resulted in the development of a new knock detection method based on high-pass filtered heat release. Different signal characteristics have been considered. The model has been developed on the basis of experimental data for a four-valve production engine, and verified over a wide range of operating conditions. For the purpose of thermodynamic investigations, the new knock detection algorithm allows the determination of the engine operating points that correspond to the knock limit, and their mean crank angle of knock onset. The thermodynamic properties of the end gas at knock onset have been discussed using a zero-dimensional two-zone model.

Reduction of fuel economy and exhaust emission at spark ignition engines with direct injection can be achieved by investigation and optimization of mixture preparation and combustion process. In this paper principle strategies of mixture preparation and combustion are discussed. Phenomena of combustion like flame radiation, flame propagation and knocking combustion are represented for different mixture preparation strategies. For detection of combustion phenomena optical fiber technique as well as new visualization device with an endoscope have been used. From the view of present knowledge, obtained with investigation of spark ignition engines with direct injection, it is an important target for future development of GDI engine technology to force activities of combustion process investigation at different mixture preparation strategies.

Flame propagation results from individual combustion cycles obtained with either the multi-optical fiber technique or with high-speed schlieren cinematography (both combined with the ion current technique) are presented and discussed for different engine operating conditions. The flame propagation results are correlated with results from in-cylinder pressure measurements, which are performed simultaneously with the flame propagation measurements. It is shown that combustion cycles which have similar in-cylinder pressure traces often show different flame propagation behavior. Therefore, conditional sampling methods which use only in-cylinder pressure traces as a criterion to select individual combustion cycles are not very accurate. Additionally, flame propagation behavior must be considered when analyzing combustion cycles.

Ziel dieser experimentellen Arbeiten war es, das Zusammenwirken zwischen Motor und Katalysator bei stationärer und instationärer Betriebsweise zu untersuchen. Als Versuchsträger diente ein 4-Zylinder-Ottomotor (1,8 ltr.), der mit einer KE-Jetronic und Schubabschaltung ausgerüstet war. Um sowohl die Rohemission des Motors als auch die Umsatzrate des Katalysators beurteilen zu können, wurde eine Abgasanalyse vor und hinter dem Katalysator vorgenommen. Zur Beurteilung der Katalysatorbeanspruchung bei den verschiedenen Randbedingungen wurden die Temperaturen innerhalb des Katalysators an verschiedenen Meßstellen mit Thermoelementen erfaßt. Die Messungen erfolgten bei 4 unterschiedlichen Kennfeldpunkten, wobei im Instationärbetrieb, ausgehend von den Ausgangslasten, in den Schubbetrieb übergegangen wurde. Nach der Schubphase wurde wieder auf die Ausgangslast zurückgesprungen.

This paper presents results on the phenomenon of knocking (detonation) during combustion in a single-cylinder spark ignition engine. The investigation of knocking combustion was made possible by observing in-cylinder flame propagation with a measuring technique that uses optical fibers coupled with photo-multipliers. The results indicate that knocking combustion appears to occur as a result of autoignition and/or acceleration of the flame front in the squish crevices. At high knock intensities, the flame front velocity can be supersonic. The occurrence of knock damage does not necessarily correspond with location of knock onset. Rather, knock damage is observed at a location where pressure waves, induced by detonation, are reflected and accompanied by pressure peaks.

Flame propagation as well as the special role of detonation waves during knocking combustion are still unsolved questions. In order to examine these phenomena during cyclic resolved knocking combustion, high-speed schlieren photography and multi optical fiber technique were applied simultaneously. The pictures were taken at a rate of 200 000 frames per second, whereas the flame radiation signals of the knocking combustion, detected with the multi optical fiber technique at 49 measuring points, were recorded with a sampling frequency of 500 kHz. The exact correlation between schlieren photography and optical fiber technique shows that knocking combustion is initiated by self ignitions in the unburned regions, clearly separated from the spark ignited flame. The complete autoignition (i.e. knocking combustion) proceeds in two stages thus showing distinct prereactions.

The objective of this study is to achieve a general understanding of gas exchange phenomena to develop a model for predicting the residual gas content. The knowledge of the cylinder-charge composition is important for the thermodynamic analysis of the combustion process of IC engines. Therefore, the amount of fresh air and fuel as well as the residual gas fraction has to be known. The residual gas mass strongly depends on valve train parameters and operating conditions. In this study, the residual gas fraction has been determined by using in-cylinder gas sampling from the combustion chamber of a 4-stroke SI engine. The gas sampling valve was flush-mounted to the combustion chamber walls. The gas samples were taken after the gas exchange and analysed for its CO2 concentration. In combination with the analysis of the exhaust gas composition, the calculation of the residual gas fraction is possible.

In this paper an estimation of efficiency potential of the engine process with Gasoline Direct Injection (GDI) is presented as well as both the advantages and todays problems of different mixture preparation concepts for the GDI engine. Furthermore examples of combustion analysis with optical measurement methods like Particle Image-Velocimetry (PIV) and spectroscopy techniques, which are important for future development steps in GDI, are shown and discussed. A validation of the numerical simulation of the stratified combustion process with data, obtained experimentally from a GDI engine, is performed and discussed. Consequently the combination of experimental and numerical methods provides both a better understanding of mixture preparation and combustion processes in GDI engines as well as an efficient development procedure for an optimized mixing and combustion process for future GDI engines.

This paper presents the results of investigations that were carried out on a single-cylinder spray-guided direct injection engine. The effects of injection pressures of up to 1000 bar on combustion and emissions at the stability limit of stratified load are presented. It is known that at low engine speeds, problems in mixture preparation occur due to insufficient in-cylinder motion at higher loads in stratified charge operation. Additionally, adverse effects appear at high engine speeds due to limited time for vaporization and mixture formation. Therefore, investigations at various engine speeds ranging from 2000 to 4000 rpm were performed. As a baseline, a production multihole injector is compared with an injector that has been specially adapted for higher injection pressures.

In this work, the potential of laser-induced ignition to improve combustion initiation and heat release in a direct-injection engine is investigated by a combined experimental and numerical investigation. Laser ignition is studied in fuel/air mixtures with homogeneous equivalence ratio fields. The results provide knowledge about minimum ignition energies and the ignition limits of laser-induced ignition. Furthermore, in mixtures with nominally identical conditions, statistical variations of the ignition success are observed experimentally. These variations can be explained, based on numerical simulations, by fluctuations in the strain rate in the turbulent in-cylinder flow. Additionally, laser ignition in engines with a spray-guided combustion mode, with strongly inhomogeneous fuel/air mixtures, was investigated.

To meet future emission standards with gasoline direct injection engines it is important to have a reliable process robustness during stratified charge operation. Especially engines with a wide spacing arrangement of fuel injector and spark plug which operate with an air-guided concept are very sensitive concerning misfire operation caused by cyclic variations of the mixture formation and transport. Primarily the turbulent in-cylinder gas motion and the interaction with the fuel injection indicate these fluctuations. To reduce these cycle-to-cycle variations and to generate a steady flow behavior an adjustable air-guiding system was developed and attached to the inlet port of a single-cylinder DI engine. The following examinations show that the air-guiding system can lead to a significant reduction of the cycle-to-cycle-variation of the in-cylinder air flow. As a result of these improvements, the deviation of imep in the fired engine decreases obviously.

A new fiber optic sensor has been used to detect knocking combustion. With this sensor it is possible to detect high frequency signals which are free from electrical and mechanical disturbance. By using the maximum signal rise of the detected optical signals for each combustion cycle, it is possible to clearly seperate knocking and non-knocking cycles. The detected maximum signal rise was used in a preliminary test as the input of a knock control system.

To operate gasoline direct injection engines at part load and in stratified mode the mixture formation has to fulfil several requirements. The complexity of this process requires - regarding a suitable mixture transportation and vaporisation of the fuel - an adjusted design of the combustion chamber and the intake ports to reliably place an ignitable mixture at ignition timing near the spark plug at any speed and load. Due to the inhomogeneous mixture distribution during stratified operation, the first combustion period is very sensitive to cycle-to-cycle variations. A reproducible mixture movement with high kinetic energy is necessary for stable engine operation with low fluctuations in the combustion process. Because of the high relevance of these facts, the effects of an adjustable air guiding system in the inlet manifold on in-cylinder flow, ignition and combustion using optical measurement techniques were investigated.

An important source for soot formation during the combustion of diesel engines with direct injection is the interaction of liquid fuel or a very rich air/fuel-mixture with the flame. This effect appears especially in modern direct injection engines where the injection is often split in a pre- and a main injection due to noise reasons. After the ignition of the pre-injected fuel a part of the main injection can interact with the flame still in liquid phase as the fuel is injected straight towards the already burning cylinder areas. This leads to high amounts of soot. The injection strategy for this experimental study overcomes this problem by separating the injections spatially and therefore on the one hand reduces the soot formation during the early stages of the combustion and on the other hand increases the soot oxidation later during the combustion. In particular an injection configuration is used which gives the degree of freedom to modify the injection in the described manner.

The reduction of emissions of future SI engines is of prime importance for their development. Hence, investigations of the formation of unburned hydrocarbons in SI engines have been the subject of intensive research for many years. The scope of this work was to investigate several pistons with different top land geometry with respect to the potential of HC reduction. The observation of flame intrusion into the top land crevice was enabled by an optical fiber measurement technique. For this, six optical probes were inserted into the cylinder liner of a production four-cylinder SI engine. The emissions were detected with a conventional exhaust gas measuring system. The results of the investigation show reductions of about 30% in the HC emission. The flame intrusion depth and the frequency of intrusion are clearly dependent on the top land geometry.

In order to meet future emission standards of small two-stroke engines (CARB 2), detailed knowledge of in-cylinder charge motion and mixture distribution is essential to be able to provide new ways of reducing exhaust emissions. The aim is to minimize fuel short circuiting accompanying the scavenging flow, which in turn leads to high HC emissions. Therefore, an experimental investigation was carried out to investigate the in-cylinder flow structure during the gas exchange process inside a small two-stroke engine. An optically accessible cylinder was fitted to a 64 cm3 two-stroke engine and the transient gas motion examined with Particle-Image-Velocimetry (PIV) under a variety of operating conditions and speeds up to 6000 rpm. The flow was investigated in two vertical cross- sectional planes through the cylinder and in a horizontal plane. The flow was observed through endoscopic optics to overcome the limitations associated with the design of an optical aperture in the small engine.

The mixture formation of a direct injection HCCI engine was optimized by a new nozzle geometry in combination with a multi-pulse injection scheme. To achieve this injection strategy, a highly flexible Piezo-Common-Rail injection system was used at the single cylinder research engine (DC BR 500, compression ratio reduced to 14:1). Optical probes for local, time resolved temperature and soot concentration measurement (Two-Color-Method) were adapted. Furthermore, a camera system was applied to detect the radiation of UV light (especially emitted by OH radicals which is an important indicator of the ignition process). So, the behaviors of different fuels in regard to the combustion process have been investigated. Diesel, SMDS and mixtures of n-heptane and iso-octane were tested with various EGR ratios, boost pressures and air/fuel ratios.