Planar Fuel-Air-Ratio-LIF for dynamic mixture-formation investigations

Controlled and well-defined mixing of fuel and air is essential for the development of new engine concepts and their combustion processes. Therefore, many kinds of optical diagnostics have been developed in the past to get a better understanding of the processes governing the mixture formation.

In 1994, Reboux et al. introduced a promising diagnostic technique for measurement of the fuel air ratio by laser-induced fluorescence (FARLIF). They used toluene as a tracer in the model-fuel isooctane and took advantage of the strong fluorescence-quenching of oxygen.

Our work is focused on the applicability of the FARLIF-concept without any tracer – with more realistic self-fluorescing fuels. Our investigations showed that a barely modified standard gasoline (“Shell Euro Super colorless”) is a good candidate for FARLIF with 266 nm excitation.

A direct verification demonstrated that this concept holds at least up to 500K at pressures above 1.3 bar and sufficient air-fraction lambda>0.2 and ongoing experiments focus on higher temperatures up to 720 K. Under the valid conditions, FARLIF-signals are pressure independent and proportional to the fuel-air-ratio, if corrected properly for absorption of the laser-excitation (see figure 1).

: Figure 1: FARLIF validation

The application of this measurement concept was demonstrated in planar LIF investigations in a flow-chamber using light sheet techniques and an intensified CCD camera. The results show that quantitative lambda-maps can be measured even in single shot experiments at combustion relevant mixture ratios (see figure 2).

: Figure 2: Planar FARLIF imaging

Furthermore, this mixture-ratio measurement technique was expanded to a FARLIF double-frame technique using a double-pulse laser and an intensified dual-frame camera. Comparable to PIV two pictures are taken in a defined time interval, showing the temporal evolution of the mixture field and its temporal derivative Using data evaluation techniques like “optical flow”, these fluorescence-double-frames yield vector maps depicting the mixture movement (see figure 3).

: Figure 3: Double pulse FARLIF imaging

Finally, this “fluorescence motion analysis” (FMA) was combined with a simultaneous standard PIV measurement in order to compare and supplement the FMA results with the actual flow field.

The combination of the methods provides a deeper insight in the dynamic mixture formation process and is used in optical engines in ongoing investigations.

Further information:

Scholz J., Röhl M., Beushausen V.: Mischungsfeldanalyse mit Fuel-Air-Ratio-LIF. Lasermethoden in der Strömungsmesstechnik, 13. Fachtagung der Deutschen Gesellschaft für Laser-Anemometrie GALA e.V., Cottbus, 6.-8.September, 2005

Scholz J., Röhl M., Wiersbinski T., Beushausen V.: Verification and Application of Fuel-Air-Ratio-LIF, 13th Int. Symp. on Applications of Laser Techniques to Fluid Mechanics, Lisbon, Portugal, 26-29 June, 2006

Scholz J., Wiersbinski T., Beushausen V.: Planare Fuel-Air-Ratio-LIF und PIV zur Gemischbildungsanalyse von Realkraftstoff, Lasermethoden in der Strömungsmesstechnik, 14. Fachtagung der Deutschen Gesellschaft für Laser-Anemometrie GALA e.V., Braunschweig, 5.-7. Sept. 2006

Scholz J., Röhl M., Wiersbinski T., Beushausen V.: Planar Fuel-Air-Ratio-LIF with Gasoline, 12th International Symposium on Flow Visualization, Göttingen, 10-14 September, 2006

Scholz J., Wiersbinski T., Beushausen V.: Kombination von FARLIF und PIV zur Gemischbildungsanalyse von Realkraftstoff in A. Leipertz (Hrsg.): Motorische Verbrennung- Aktuelle Probleme und moderne Lösungsansätze, Bericht zur Energie- und Verfahrenstechnik (BEV) 7.1, ESYTEC, Erlangen, S. 293-302, 2007

Scholz J., Wiersbinski T., Beushausen V.: Planar Fuel-Air-Ratio-LIF with Gasoline for dynamic mixture-formation investigations, SAE-world congress, Detroit, USA, April 2007, SAE Paper 2007-01-0645

Scholz J., Wiersbinski T., Ruhnau P., Kondermann D., Garbe C.S., Hain R., Beushausen V.: Double-pulse planar-LIF investigations using fluorescence motion analysis for mixture formation investigation, Experiments in Fluids, Vol. 45, Issue 4, pp 583-593, 2008

Sponsorship:

Schwerpunktprogramm SPP 1147 "Bildgebende Messverfahren für die Strömungsanalyse" der Deutschen Forschungsgesellschaft DFG

Co-operation partners:

Universität Göttingen, DPI
Universität Heidelberg, IWR
Universität Mannheim, CVGPR
Universität Münster, Inst. F. Angew. Physik
TU Braunschweig, ISM
FH Hildesheim Holzminden Göttingen