Fig. 1. Schematic diagram of the energy level transition of the LIF

Fig. 2. Schematic diagram of the PLIF laser sheet

Fig. 3. Jet flame obtained by single-species PLIF imaging. (a) Experimental system; (b) HCO PLIF^[56]; (c) CH₂O PLIF; (d) CH PLIF^[61]; (e) OH PLIF^[62]; (f) CH₃ PF-LIF^[63]

Fig. 4. Instantaneous flame structure acquired by OH PLIF in scramjet engines. (a) Hydrogen injection^[66]; (b) ethylene injection^[31]; (c) ethylene injection with high-resolution imaging^[69]

Fig. 5. Instantaneous flame structures obtained by different PLIF methods. (a) CH PLIF^[77]; (b) CH PLIF^[31]; (c) CH PLIF^[76]; (d) CH₂O PLIF^[78]

Fig. 6. Multi-species PLIF imaging of the jet flames. (a) Jet flame image^[27]; (b) simultaneous CH₂O/OH PLIF image^[27]; (c) simultaneous CH₂O/OH/HCO PLIF image^[61]; (d) simultaneous measurement images of the CH₃ PF-LIF and CH₂O PLIF

Fig. 7. Synchronous PLIF image of the cavity-stable flame scramjet combustion chamber. (a) spanwise plane; (b) streamwise plane^[76]

Fig. 8. Quantitative extraction of flame structure parameters based on PLIF. (a) Quantitative extraction of flame surface, flame surface density and progress variables based on OH PLIF^[83]; (b) thickness of the reaction zone of the high turbulent flame^[86]; (c) CH₃ PF-LIF/CH₂O PLIF simultaneous measurement image and ridge extraction results; (d) OH PLIF-based extraction of scramjet f

Fig. 9. Application of different tracer PLIF in the characterization of engine fuel distribution. (a) Acetone PLIF^[106-107]; (b) kerosene PLIF^[108]; (c) NO PLIF^[109]; (d) NO PLIF^[110]; (e) toluene PLIF^[111]; (f) f

Fig. 10. Application of tracer-PLIF to measure the equivalence ratio and fuel distribution in the different engines. (a) 3-pentanone PLIF in a V-shaped flame^[35]; (b) acetone PLIF in a gasoline engine^[118]; (c) toluene PLIF in a gasoline engine^[118]; (d) TMB PLIF in a gasoline engine^[118]; (e) toluene PLI

Fig. 11. Application of tracer-PLIF in measuring the temperature distribution of different engines. (a) Temperature distribution of the expansion tube using toluene PLIF^[125]; (b) temperature distribution of the supersonic expansion tube using toluene PLIF^[126]; (c) temperature distribution of HCCI engine using acetone/3-pentanone PLIF^[127]; (d) temperat

Fig. 12. Schematic diagram of the TLAF technique. (a) Three-level diagram of the In atom^[37]; (b) schematic diagram of the TLAF measurement system^[39]

Fig. 13. Temperature characteristics of typical atomic elements. (a) Temperature sensitivity of the atomic elements for TLAF; (b) variation of the particle number distribution of the upper energy level of the tracer atom with temperature^[48]

Fig. 14. Different seeding methods for the In atom. (a) InCl₃ solution seeding^[137]; (b) In seeding by laser ablation^[139]; (c) In₂O₃ seeding by flame spay pyrolysis^[140]; (d) TMI seeding by spray pyrolysis^[141]

Fig. 15. Combustion filed temperature distribution measured by linear TLAF with In atoms as tracers. (a) TLAF and Mie scattering image^[144]; (b)^[39]-(c)^[37]average temperature field distribution of laminar premixed flame; (d) fluorescence transient distribution image of methane/air jet premixed flames^[140]

Fig. 16. Combustion filed temperature distribution measured by nonlinear TLAF with In atoms as tracers. (a) Temperature distribution in a laminar premixed flame^[145]; (b) temperature distribution in a non-premixed flame^[150]; (c) temperature distribution in a non-premixed flame^[147]; (d) temperature distribution in a slot burner^{[Download full size}

Fig. 17. Schematic diagram of the MTV technology

Fig. 18. Typical profile of velocimetry images. (a) NO PLIF images in a supersonic boundary layer^[157]; (b) velocity distribution in a supersonic boundary layer^[157]; (c) NO PLIF images in a low speed jet flow^[155] ; (d) velocity distribution in a low speed jet flow^[155]

Fig. 19. KTV technique. (a) Schematic of the KTV speed measurement device; (b) Typical speed measurement results^[158]

Fig. 20. Profile image of the typical mean velocity. (a) Freestream^[159]; (b) boundary layer^[174]

Fig. 21. HTV images. (a) Single-shot HTV image^[180]; (b) images of the mean velocity and RMS fluctuation^[181]

Fig. 22. HTV images. (a) HTV image of unreacted flow field; (b) HTV image of combustion flow field; (c) velocity distribution of unreacted flow field; (d) velocity distribution of combustion flow field^[40]

Fig. 23. High-repetition PLIF images in scramjet engines. (a) 10 kHz OH PLIF images^[189]; (b) 100 kHz CH₂O PLIF images^[41]

Fig. 24. 3D reconstruction of the flame structure. (a) Experimental schematic diagram; (b) 3D reconstruction of the OH radicals^[194]

Fig. 25. VLIF technique. (a) Schematic of the experimental setup; (b) three-dimensional reconstruction of the CH radicals in a flame^[195]

Fig. 26. Simultaneous measurement images of PLIF/PIV. (a) PIV and CH₂O/OH PLIF images for the bluff body flame^[46]; (b) PIV and OH PLIF images for the lifted flame^[200]; (c) PIV, kerosene PLIF and OH PLIF images for the swirling flame^[45]

Fig. 27. Simultaneous measurement images of PLIF and Rayleigh scattering. (a) OH/CH₂O PLIF and Rayleigh scattering images^[212]; (b) CH₂O/OH/CH PLIF and Rayleigh scattering images^[213]; (c) CH₂O PLIF and Rayleigh scattering images^[214]