Research of Two-Dimensional Reconstruction of Combustion of Tunable Diode Laser Absorption Spectroscopy Based on Virtual Beam and Re-Projection Method

Aiming at the problem of two-dimensional reconstruction of gas concentration and temperature under incomplete projection data, a two-dimensional reconstruction technique based on a virtual beam and re-projection method is proposed. This method uses the finite measurement projection data to obtain the virtual projection at different positions of the same angle, improves the reconstruction quality by increasing the number of beams. The re-projection method was used to acquire the virtual projection data of other angles, and finally realize the two-dimensional reconstruction of the combustion chamber component temperature. Two H2O absorption line of 7185.6 and 7444.35 cm(-1) in the near-infrared band was used to conduct simulation calculation on the 49 X 49 grid combined with 21 measurement beams, and the measurement beams arrangement and virtual beams arrangement were optimized. Compared with the traditional algebraic reconstruction technique using a smoothing factor, the reconstruction precision of the virtual beam and re-projection method is obviously improved, and the influence of artificially selected smoothing factor eliminated. The calculation results show that the reconstruction error decreases with the increase in the number of re-projection operations. It tends to be stable after the number of re-projections reaches ten times. The temperature field reconstruction error is less than 5.76% under 5% noise conditions, and the concentration field reconstruction error is less than 8.83% so the measurement noise has little influence on the reconstruction result of the combustion field. The analysis of bimodal and multimodal combustion field models in the temperature range of 600 similar to 1200 K was carried out to verify the ability of virtual beam and re-projection method to reconstruct the two-dimensional concentration and temperature of gas components in the combustion field under different working conditions. The results are of great significance for promoting the theoretical research and engineering application of laser absorption spectroscopy in two-dimensional combustion field reconstruction.