## 3 Results and Discussion
### Intermediate Reaction Products (Small Molecules and Free Radicals) at Different WOMR  
In Figure 2a, the variation of the reaction rate of H\({}_{2}\)O\({}_{2}\) with different water/oil mass ratio is exhibited. Combined with Figures 1a and 2b,c, the generation of H\({}_{2}\)O\({}_{2}\) occurred between 0.001 s and 0.002 s and the consumption occurred between 0.007 s and 0.008 s. When the water mass fraction increases from 10% to 30%, the response of the reaction of H\({}_{2}\)O\({}_{2}\) is lagged behind, and the maximum generation rate is 2.77%, 5.67%, 8.38% lower than that without water, and the maximum consumption rate is 3.55%, 6.80%, 13.01% lower than that without water. It shows that both reaction delay and peak value decrease cause the increase of heat needed for activation reaction at the same activation energy and reaction temperature when water is introduced to inhibit the chain reaction. The existence of water plays a role in controlling the rate of the main element reaction.  
Figure 3 shows the reaction rate of H\({}_{2}\) at different WOMR. Hydrogen has the advantages of low ignition energy, high flame propagation speed, high diffusion rate and wide ignition limit [34; 35; 36]. Therefore, hydrogen addition can effectively increase combustion stability. The primary hydrogen production reaction in this mechanism is: NH + H\({}_{2}\)O <=> HNO + H\({}_{2}\) (#1032 elementary reaction in Chen mechanism plus GRI mech3.0), in which the positive reaction requires very high activation energy, \(E_{\text{a}}\) = 13.850 kJ/mol. With the increase of water, the temperature of the system decreases and the generation rate of H\({}_{2}\) decreases significantly, and the reaction is pushed back. But another elementary reaction NH + NO <=> N\({}_{2}\) + OH (#1033 elementary reaction in Chen mechanism plus GRI mech3.0) mainly occurs in the reductive environment. So under this circumstance, the above two steps will result in a scramble for the NH radical. Then the final result of the effect is that the NH is oxidized by excessive H\({}_{2}\)O, so the reduction process of NO is hindered, resulting in a slight increase of the yield of NO.  
Figure 2: Reaction rate of H\({}_{2}\)O\({}_{2}\) at different WOMR (\(\lambda\) = 1). (**a**) Global profile comparison; (**b**) Detail profile comparison 1; (**c**) Detail profile comparison 2.  
From Figure 4, it can be seen that with the increase of water content, the reaction rates of OH, HO\({}_{2}\), H and O decrease in varying degrees and are accompanied by the back shift of the peak value. At the same time, there is also the transfer process of material and energy between the four intermediate products. These reactions occur at the high temperature stage at the end of the first stage. Because of the high temperature, the intense reaction, the short reaction time, and the competition for the same components, there is a relationship between these reactions, forming a closed loop, as shown in Table 2. In a moment, the concentration of OH and O increases sharply, which causes the generation of many active centers. Ultimately, the activation center concentration is the key factor affecting the combustion of the fuel. This is the starting point of the second stage combustion. The concentration of OH and O decreases after some chain carrier is destroyed. Then the system reaches the steady state gradually.  
Figure 4: _Cont._  
Figure 3: Reaction rate of H\({}_{2}\) at different WOMR (\(\lambda=1\)).  
Figure 4: Reaction rate of OH, HO\({}_{2}\), H and O at different WOMR (\(\lambda=1\)). (**a**) Reaction rate of OH; (**b**) Reaction rate of HO\({}_{2}\); (**c**) Reaction rate of H; (**d**) Reaction rate of O.