## 4 Conclusions  
In this paper, a numerical investigation of the action mechanism of H, O, OH, HO\({}_{2}\), H\({}_{2}\) and H\({}_{2}\)O\({}_{2}\) on the generation of nitrogen oxides with different air/fuel ratio and different WOMR was completed. The main conclusions are summarized as follows:  
* An obvious result of two stages reaction processes is obtained by the numerical method. When the temperature reaches to 1000 K, the temperature rises sharply, and the mixture enters the high temperature oxidation stage. The rapid consumption of H\({}_{2}\)O\({}_{2}\) and the rapid generation of OH indicates the generation of the flame surface. * With the increase of water mass fraction, the response of the reaction of free radicals (H, O, OH, HO\({}_{2}\), H\({}_{2}\)O\({}_{2}\)) is lagged behind, meanwhile the peak value of the reaction rate decreases due to the increase of heat needed for activation reaction at the same activation energy and reaction temperature. When the water content increases 10%, the maximum generation rate of NO, N\({}_{2}\)O, NO\({}_{2}\) decreases by 15.24%, 9.21%, 14.78% on average, respectively. * According to the correlation results, maximum production rate of NO and the mole fraction of O, OH, H\({}_{2}\) have significant correlation relation; maximum production rate of N\({}_{2}\)O and the mole fraction of O, OH, HO\({}_{2}\), H\({}_{2}\) have significant correlation relation; maximum production rate of NO\({}_{2}\) and the mole fraction of O, OH, HO\({}_{2}\), H\({}_{2}\)O\({}_{2}\) have significant correlation relation. In contrast, OH, O and H\({}_{2}\) play a more significant role in the common influence of the generation of nitrogen oxides. Figure 9: Sensitivity diagram of OH, O, HO\({}_{2}\), H\({}_{2}\) (at the time of the second stage starting point). (a) Normalized sensitivity of OH (**b**) Normalized sensitivity of O; (**c**) Normalized sensitivity of HO\({}_{2}\) (**d**) Normalized sensitivity of H\({}_{2}\). * According to the sensitivity results, elementary reactions #1 and #16 promote the generation of OH and O at the beginning of the second stage, but elementary reaction #9, #13 and #20 have a negative effect. Meanwhile the result is just opposite for effect of HO\({}_{2}\) and H\({}_{2}\). **Supplementary Materials:** The supplementary material contains the mechanism document used in this article. The following are available online at [[http://www.mdpi.com/2076-3417/8/4/490/s1](http://www.mdpi.com/2076-3417/8/4/490/s1)]([http://www.mdpi.com/2076-3417/8/4/490/s1](http://www.mdpi.com/2076-3417/8/4/490/s1)), mech.txt: it records the chemical reaction mechanism; thermo.txt: it records the thermodynamic parameters of the species; transport.txt: it records the transport parameters of the species. **Acknowledgments:** This work is supported by the National Natural Science Foundation of China (NSFC, 51276079) and the Project 2017042 supported by the Graduate Innovation Fund of Jilin University. The authors appreciate the insightful comments and suggestions from the reviewers and the editor. **Author Contributions:** [PERSON] and [PERSON] conceived, designed and performed the experiments; [PERSON] analyzed the data; [PERSON] and [PERSON] wrote the paper. **Conflicts of Interest:** The authors declare no conflict of interest.