Luminescence interference to two-colour toluene laser-induced fluorescence thermometry in a particle-laden flow

We present the use of two-colour toluene planar laser-induced fluorescence (LIF) to obtain spatially resolved measurements of the gas temperature ($$T_\mathrm{g}$$) in a particle-laden turbulent flow under sufficiently dense particle loading that the interference from laser interactions with the particles is significant. The effect of the ratio of volumetric flow rates of the particle phase to the gas phase ($$\phi$$) on the accuracy and precision of two-colour toluene LIF thermometry was systematically investigated for three particle materials, alumina, zinc activated zinc oxide (ZnO:Zn) and polymethyl methacrylate (PMMA), each of which has differing interactions with the excitation laser. The PMMA particles were spherical and mono-disperse with diameters of 6 to $$40\, \upmu \hbox {m}$$, while the alumina and ZnO:Zn particles had diameters in the range 1–40  $$\upmu \hbox {m}$$ and 2–200 $$\upmu \hbox {m},$$ respectively. The results show that the accuracy of the gas temperature measurement is insensitive to particle size for the PMMA particles, but dependent on the instantaneous particle loading. Importantly, reliable measurements can be performed in the dense two-way coupling regime, with the measurement being accurate to within 5 °C for $$\phi$$ < $$2.5\times 10^{-4}$$ for the PMMA particles and for $$\phi<$$$$7.6\times 10^{-4}$$ for the alumina and ZnO:Zn particles.