5.2. Comparison between numerical simulation and experimental results

The comparison between the numerical simulations and the experimental results in the methane/air laminar partially premixed flame under different equivalence ratios is shown in Figure 6. The values of red translucency are the total uncertainties of the corresponding measured points.

From Figure 6, we can draw the following three conclusions:

1. In the range of equivalence ratio 0.7–1.2, the calculated results and the experimental values have the same variation trend with increasing the axial distance above the burner. The OH concentration increases rapidly to the maximum and then gradually decreases with the increase of axial distance, remaining unchanged at last. However, the experimental OH concentrations in the burnout zone decrease faster than the calculated results under certain equivalence ratios (e.g., equivalence ratios 0.8 and 0.9). The reason for this phenomenon mainly lies in the fact that the temperature results given by the GRI-Mech 3.0 mechanism are basically kept unchanged in this region, while the experimental temperature will decrease with increasing the axial distance.

Figure 6. Comparison between experimental and numerical results of OH concentration in the central axis.

radical group gradually moves toward both sides of the flame, and the amount of OH radicals in the middle region is decreasing gradually with the increase of the equivalence ratio from 0.7 to 1. When the flame is burning at the rich-burn condition, as shown in Figure 5, the OH concentration profiles have changed greatly. That is, as the equivalence ratio continues to increase from 1.1 to 1.4, the two strong OH radical bands are formed on both sides of the flame. Meanwhile, the OH radical density in the middle region of flame

Figure 5. Variations of two-dimensional OH concentrations with equivalence ratios (Φ = 1.1–1.4). (a) Φ = 1.1, (b) Φ = 1.2,

The comparison between the numerical simulations and the experimental results in the methane/air laminar partially premixed flame under different equivalence ratios is shown in Figure 6. The values of red translucency are the total uncertainties of the corresponding

1. In the range of equivalence ratio 0.7–1.2, the calculated results and the experimental values have the same variation trend with increasing the axial distance above the burner. The OH concentration increases rapidly to the maximum and then gradually decreases with the increase of axial distance, remaining unchanged at last. However, the experimental OH concentrations in the burnout zone decrease faster than the calculated results under certain equivalence ratios (e.g., equivalence ratios 0.8 and 0.9). The reason for this phenomenon mainly lies in the fact that the temperature results given by the GRI-Mech 3.0 mechanism are basically kept unchanged in this region, while the experimental temperature will

5.2. Comparison between numerical simulation and experimental results

From Figure 6, we can draw the following three conclusions:

decrease with increasing the axial distance.

decreases sharply.

(c) Φ = 1.3, (d) Φ = 1.4.

100 Laser Technology and its Applications

measured points.


and disadvantages of current quantitative PLIF technologies for species concentration measurements in flames are reviewed. And the latest works on the quantification of species concentration using PLIF in combustion are introduced. Thirdly, a non-calibration quantitative PLIF technology, named bidirectional PLIF, which is independent of collisional quenching effect, has been introduced in detail. As the current measurement equation of effective peak absorption cross section provided by Versluis et al. is found to be not applicable to the case of weak absorption, the revised experimental equation has been proposed in this chapter. At last, the twodimensional spatial distributions of OH concentration and its variations with the equivalence ratios have been investigated in the methane/air partially premixed flame. The comparison between the experimental OH concentrations and the numerical simulation results has also been made under the equivalence ratios of 0.7–1.4. The result indicates that the OH concentration profiles measured by bidirectional PLIF are in good agreement with the predictive values

Quantitative Planar Laser-Induced Fluorescence Technology

http://dx.doi.org/10.5772/intechopen.79702

103

This research is financially supported by the National Key Scientific Instrument and Equipment Development Projects of China (No. 2012YQ040164) and the National Natural Science Foundation of China (Grant Nos. 61275127 and 91441130). The author would like to thank Prof. Xin Yu, Dr. Jiangbo Peng, and A/Prof. Jianlong Zhang et al. for providing many valuable

1 National Key Laboratory of Science and Technology on Tunable Laser, Harbin Institute of

3 Institute of Optical Target Simulation and Test Technology, Harbin Institute of Technology,

[1] Hanson RK. Planar laser-induced fluorescence imaging. Journal of Quantitative Spectroscopy and Radiative Transfer. 1988;40(3):343-362. DOI: 10.1016/0022-4073(88)90125-2 [2] Xavier P, Vandel A, Godard G, et al. Investigation of combustion dynamics in a cavitybased combustor with high-speed laser diagnostics. Experiments in Fluids. 2016;57:50.

2 Institute of Opto-Electronics, Harbin Institute of Technology, Harbin, China

performed by GRI-Mech 3.0 mechanism.

Zhen Yang1,2,3\*, Xin Yu1,2, Jiangbo Peng1,2 and Jianlong Zhang<sup>3</sup>

\*Address all correspondence to: sailoryz@163.com

DOI: 10.1007/s00348-016-2135-7

Acknowledgements

insights and numerous help.

Technology, Harbin, China

Author details

Harbin, China

References

Figure 7. Comparison between experimental data and numerical simulation of peak OH concentration.

premixed gas will rise rapidly after flowing out from the burner and produce the chemical reaction, resulting in generating a large number of OH radicals. However, the temperature rising process of the premixed gas has not been taken into account in the numerical simulation. On the contrary, it is considered that the gas temperature near the outlet of burner is still in an ideal unheated state. Therefore, the measured OH concentrations are higher than the calculation results in the upstream of reaction zone.

The comparison results for the peak concentration under the conditions of different equivalence ratios have also been made, as shown in Figure 7. It can be clearly seen that the experimental results are smaller than the calculated values. The reason has already been analyzed before, so it is no longer mentioned here. Another notable phenomenon is that the measured OH concentration has not reached the maximum under the equivalent ratio of 1.0, but the peak OH concentration occurs in the lean-burn zone under the equivalence ratio of 0.9. The above experimental result indicates that even if the equivalence ratio of the premixed gas is set to 1.0, the fuel molecules still cannot be completely consumed in the actual combustion process. Therefore, we speculate that the OH reaction rate predicted by the simulation may be higher than the experimental value under the condition of stoichiometric ratio.

### 6. Conclusions

In conclusion, this chapter first reviews the developments of planar laser-induced fluorescence and briefly analyzes the existing problems of quantitative PLIF technology. Then, the advantages and disadvantages of current quantitative PLIF technologies for species concentration measurements in flames are reviewed. And the latest works on the quantification of species concentration using PLIF in combustion are introduced. Thirdly, a non-calibration quantitative PLIF technology, named bidirectional PLIF, which is independent of collisional quenching effect, has been introduced in detail. As the current measurement equation of effective peak absorption cross section provided by Versluis et al. is found to be not applicable to the case of weak absorption, the revised experimental equation has been proposed in this chapter. At last, the twodimensional spatial distributions of OH concentration and its variations with the equivalence ratios have been investigated in the methane/air partially premixed flame. The comparison between the experimental OH concentrations and the numerical simulation results has also been made under the equivalence ratios of 0.7–1.4. The result indicates that the OH concentration profiles measured by bidirectional PLIF are in good agreement with the predictive values performed by GRI-Mech 3.0 mechanism.
