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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 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.

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.

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).

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.

In this paper optical investigations of a gasoline direct injection engine with narrow spacing arrangement of spark plug and injector are presented. For the combustion analysis spectroscopy techniques based on the fiber technique are used. With this measurement technique information about soot formation and temperature progression in the combustion chamber is obtained. Furthermore a validation of numerical simulation of the stratified combustion with data obtained experimentally, is performed and discussed.