Figure 2 Flame processing images.
Flame morphology and flame height
variations were recorded by digital and high-speed cameras. In each
experiment, the two cameras were set at a certain distance from the cup
burner, so the entire flame pattern could be recorded.
In this study, Otsu’s method was
used to process flame images to obtain flame height, and flame height
(h) was defined as the vertical distance from the nozzle to the flame
tip[19, 20]. First, the original images were converted to gray scale
images. each pixel point had its own luminance value in the gray scale
image and the threshold value of the image was obtained objectively by
using Otsu method. Then based on the luminance value and threshold
value, the binary image could be obtained[21].
Finally, the binary image was
processed to become the intermittency distribution image by processing
program (Figure 2), which showed the probability of the flame occurring.
2.2 Theoretical
calculations
In order to explore the detailed path of the fire extinguishing
mechanism, Gaussian 16 was used for theoretical calculations, and Gauss
view was used to view the optimized geometries of space[22, 23]. On
the basis of DFT calculations,
B3LYP/6-311++G (d, p) base sets were used for calculations. Reactants,
products, transition states (TSs) and intermediates (IMs) were analyzed
by DFT calculations, and the above calculation results were verified by
using virtual frequencies, and there were no virtual frequencies for
reactants, IMs and products, but only TSs had virtual frequencies[24,
25]. Then, the relationship and transformation relationship between
the reactants and the products were analyzed using IRC theory.
Meanwhile, in order to verify the accuracy of the reaction energy
calculation value, single-point energy calculation and zero-point energy
correction were performed on all stationing points. A more precise
energy value was calculated at the
CCSD/aug-cc-pVDZ level, the
optimized structures were also employed in a series of single-point
energy calculations by using coupled-cluster theory, and the correctness
of each reaction path was verified to calculate the zero-point
vibrational energy (ZPE) at the CCSD/aug-cc-pVDZ level[26, 27]. The
energy barrier is the energy difference between the TSs and the
reactants.