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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.

Given the fact that, in an endeavor to achieve the goals of engineering for a trade-off between cleaning up exhaust emissions and maximizing fuel economy, two main paths are being followed in advancing and optimizing SI-engine operating strategy in the upper part-load range. On the one hand, homogenization and operation in the compression ignition mode seem to offer a promising means of minimizing NOx emission by keeping the combustion temperature below the formation borderline and accepting a high cylinder-pressure gradient to obtain benefits in fuel economy. On the other hand, there are ambitions to widen the range of stratified operation using a supercharger or turbocharger. This way, efficiency of the engine cycle can be improved by operating at a higher global air-fuel ratio and, with this, a higher polytropic exponent, thereby taking the efficiency chain to a higher level.

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.

Understanding the processes regarding fuel injection, vaporization and combustion during cold start is very important in order to reduce the HC-emission of gasoline engines. To learn more about the cold engine start-up process an experimental study on a 4.2 liter eight cylinder engine with gasoline direct injection was carried out. Parameters such as injection and ignition timing as well as the injection quantity were varied to get information about their effect on the combustion process and speed rise. Especially during engine run-up it is important to investigate every subsequent combustion. Therefore the engine was equipped with high pressure indication in each cylinder. The transient pressures and the instantaneous crankshaft speed of the engine were recorded by means of an indication system. Additionally a fast response flame ionization detector (FRFID) was applied to measure the transient HC-emissions during the first cycles of the engine.

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.

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.

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 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.

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.

This paper analyses the scavenge process of a conventional two-stroke engine in order to find ways to significantly reduce the scavenge losses by applying a combination of 1D and 3D simulation procedures. A special evaluation method was developed which allows a clear distinction between the main hydrocarbon loss mechanisms. Furthermore, the paper presents an approach to simulate the highly turbulent combustion at a speed of 9000 rpm. The results of the numerical investigations are compared with experimental results. The engine chosen for this purpose was a 64 cm3 four-port production two-stroke engine. The CFD calculations were performed using the finite volume CFD code STAR-CD. The mesh generation process was automated using pro*am. Combustion was modelled with the one-equation Weller flamelet model. The results of the present study show that the combination of 1D and 3D simulation procedures is a powerful tool for further investigations (e.g. stratified charge, GDI).

Small two-stroke engines enjoy wide-spread acceptance in the field of hand-held outdoor equipment due to performance advantages over competing technologies. The main issue with these engines is their high hydrocarbon emission, which makes it difficult to comply with future emission laws such as the 2005 standards for small handheld engines of the U.S. Environmental Protection Agency (EPA). As a result, considerable research and development work is currently being carried out both in industrial and public research facilities to improve the hydrocarbon emission performance of two-stroke engines. Major emission reductions are expected from stratified scavenging concepts. However, the development and tuning of stratified scavenging engines requires comprehensive knowledge of the flow processes in the ports and inside the engine cylinder.

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.

The loss of momentum of the gas-core inside inlet manifolds of four-stroke engines is characterized by loss coefficients. Usually these coefficients are obtained by experimental investigations of the flow through cylinder heads under steady-state conditions. The dynamic behavior of the gas motion under real conditions due to acceleration and vibration of the gas-core as well as the influence of the gas motion due to the exhaust can not be described by these coefficients. Therefore a basic investigation of the unsteady flow under real engine conditions has been performed. The aim was to develop a simple method to characterize the inlet flow behavior under real conditions and to define a dynamic loss coefficient. The mass flow rate was determined by time resolved pressure data inside the suction pipe and a simple numerical calculation method considering unsteady flow conditions. The verification of calculated flow velocities was performed by using Particle-Image-Velocimetry.

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.

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.

The main objectives of this investigation are the visualisation of the flame propagation depending on different boundary conditions. Turbulence intensities, wall-temperatures and an air-fuel ratios were varied in a wide range. For the experiments a rapid compression machine with a quadratic piston and a good optical access is used which allows to observe the entire burning. With an additionally integrated turbulence generator it is possible to create a defined turbulence field in the burning chamber.

Knowledge of flame propagation enables a more detailed description of the combustion processes as well as assessing the influences of engine operating conditions and design parameters, particularly in view of efficiency improvements and pollutant reduction. Flame propagation in a single-cylinder spark-ignition engine is studied by means of a measuring technique using lightconductors coupled with photo-multipliers. The propagation process is monitored through a large number of optical probes arranged in a matrix in the combustion chamber. The spatial flame contour, the flame volume, and the flame front velocity as a function of time are furnished from these measurements. The investigations show the formation of quench zones ("flame quenching") not penetrated by the flame directly above the piston towards the end of the expansion phase at extremely lean operating conditions.

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.

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.