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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.

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.

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.

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.