Two-step tomographic reconstructions of temperature and species concentration in a flame based on laser absorption measurements with a rotation platform

We present a system for accurate tomographic reconstruction of the combustion temperature and H₂O vapor concentration of a flame based on laser absorption measurements, in combination with an innovative two-step algebraic reconstruction technique. A total of 11 collimated laser beams generated from outputs of fiber-coupled diode lasers formed a two-dimensional 5×6 orthogonal beam grids and measured at two H₂O absorption transitions (7154.354/7154.353 cm⁻¹ and 7467.769 cm⁻¹). The measurement system was designed on a rotation platform to achieve a two-folder improvement in spatial resolution. Numerical simulation showed that the proposed two-step algebraic reconstruction technique for temperature and concentration, respectively, greatly improved the reconstruction accuracy of species concentration when compared with a traditional calculation. Experimental results demonstrated the good performances of the measurement system and the two-step reconstruction technique for applications such as flame monitoring and combustion diagnosis.