Two RR Lean Direct Injection (LDI) injector versions with different amounts of pilot swirl were investigated. Experiments, performed at elevated pressure and temperature, corresponding to engine conditions at idle include Mie scattering. LII and absorption measurements are used for soot concentration within the primary zone. The soot emission at the outlet is measured by an SMPS instrument. These experimental studies are complemented with PIV measurements. The acquired data allows evaluation of the combustion process from the liquid phase, followed by evaporation, reaction and finally soot production with high spatial resolution.

The change of swirl produced rather moderate changes in the flow field, nevertheless qualitative changes in the fuel placement were observed. Starting from there, differences in heat release and soot formation can be explained, which lead to larger changes of soot emission.

These observations show that a good knowledge of the interaction of gas and liquid phase is necessary to predict the occurrence of behavioral changes in the operating regime.

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