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A single cylinder engine was modified to study the potential of reducing fuel consumption and emissions in stratified, direct injection, spark ignition engines with the use of air-assisted nozzles. The spray angle of the nozzle was varied (60° and 90°), and two injection strategies were investigated: (I) the fuel was injected in the nozzle prior to transportation into the chamber via the air flow and (II) the fuel was injected directly into the air flow. The results of the engine experiments were compared with the spray characteristic of each configuration. To facilitate the comparison, two-dimensional images of the sprays were recorded under atmospheric conditions. The fuel was visualized using Planar Laser-Induced Fluorescence (PLIF). The optical chamber was equipped with three optical accesses and a standard injection system from a production engine.

We report quantitative experimental investigations on the air/fuel distribution in the combustion chamber of a spark ignition engine prior to ignition and during the first stages of combustion. A four cylinder VW four-stroke engine was modified to give optical access to the combustion chamber via the piston. The fuel concentration was visualised by planar laser-induced fluorescence (PLIF). The choice of an appropriate fuel dopant is very important. Several properties have to be considered simultaneously. The most crucial influence results from the sensitivity to quenching by oxygen. Since fuel distributions recorded at different engine operating conditions wore to be compared on a quantitative scale, this effect had to be taken into account most carefully. The long fluorescence lifetime and the extraordinarily low quenching rate of vapour-phase fluoranthene in a high pressure environment as pertaining to engines led to its choice as dopant.

The quality of mixture preparation in the manifold of a SI engine has a strong influence on performance, exhaust emissions and fuel consumption. In modern gasoline engines the injectors are located close to the inlet valves to improve response under transient load conditions. Therefore the time for atomisation, evaporation and the homogeneous mixing of the fuel and air is very short. In fact a large fraction of the fuel droplets generated by the injector impact the manifold wall or inlet valve because evaporation is not fast enough. These droplets form a liquid fuel film on the wall. The result is a deterioration of the charge quality inside the combustion chamber due to liquid droplet and ligaments originated from the fuel film, especially at low temperatures. We report experimental investigations on spray formation and fuel film development in the intake of a spark ignition engine. The measurement techniques are based on laser-induced fluorescence.