Spray Formation Observation and Fuel Film Development Measurements in the Intake of a Spark Ignition Engine

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. The mixture formation is visualised by planar laser-induced fluorescence (PLIF), whereas the fuel film development was characterised and quantified by an advanced optical fiber technique.

Special emphasis is placed on the study of the spray droplets leaving the injector and the development of the fuel film after impingement on the manifold wall. Temporally and spatially highly resolved images of the fuel spray, furthermore the fuel film development were obtained cycle resolved for different engine operating conditions. In order to relate these results to specific engine conditions the intake pressure and the exhaust gas emissions were recorded. Thereby the quantity of fuel injection, time of injection, engine speed and time of inlet valve opening were varied. The studies enabled the optimisation of the injection process by modifying the injection timing and parameters.