Planar Fuel-Air-Ratio-LIF with Gasoline for Dynamic Mixture-Formation Investigations

The investigations performed serve to develop a 2D measurement technique for dynamic mixture formation analysis of fuel and air with almost standard gasoline (Euro Super colorless, without the low volatile bitumen constituents). A measurement concept for fuel-air-ratio detection by laser-induced fluorescence (FARLIF) is validated. The concept is based on 266nm Nd-YAG-laser excitation of the self-fluorescing gasoline and is validated for mixture pressures above 2.5 bar, sufficient air-fraction λ ≥ 0.4 and temperatures at least up to 548 K. The mixture temperature is shown to affect the FARLIF-intensities.

The technical feasibility of FARLIF-imaging with almost standard gasoline is successfully demonstrated. Single-shot measurements of transient mixing fields of gasoline and air at engine relevant gas conditions are performed and quantitative fuel-air-ratio maps are generated. The functionality of this technique was further expanded to a double-pulse FARLIF-imaging technique, giving additionally insight into mixture-formation dynamics. For this purpose two different data evaluation methods are introduced: The first provides temporal derivative fields of the equivalence ratio, showing where and how the mixture distribution changes. The other evaluation method quantifies the motion of mixture structures (fluorescence motion analysis, FMA). All this information can be drawn out of one single measurement only!

Finally, double-pulse FARLIF-imaging was combined with simultaneous PIV measurements. It is shown that the combination of FMA and PIV gives fast access to structure motion and gas velocity field (which do not need to be the same), simultaneously providing the actual fuel-air-ratio map and giving the possibility to calculate its temporal derivation.