# Construction of a Chemical Kinetic Mechanism of Five-Component Surrogate Fuel for RP-3 Kerosene
## 3 Modification of Kinetic Parameters for Mechanism of Surrogate Fuel Mixture
### Modification of Dynamic Parameters
This demonstrates that in the low-temperature region, the ignition and combustion processes ofthe fuel are primarily governed by the initial oxidation and dehydrogenation reactions of long-chain large-molecule fuels. As depicted in Figure 7b, at the medium temperature of 800 K, there are notable differences between the reactions with larger sensitivity coefficients and those in the low-temperature region. Under this temperature condition, small-molecule reactions such as R212, R158, R14, and R12 begin to emerge among the reactions that influence the temperature. Among them, R14 has the greatest sensitivity coefficient, followed by R158. Since reaction R14 is the reaction of two OH radicals to generate H\({}_{2}\)O\({}_{2}\) radicals under the action of a third body, this reaction promotes the temperature rise in the fuel system. In terms of reactant types, there are still six large-molecule reactions in the fuel, accounting for more than half, which still exert considerable influence on the ignition delay time. The sensitivity reaction results under the high-temperature working condition of 1200 K are presented in Figure 7c. At the high-temperature stage, although there are still large-molecule reactions such as R104, R106, R235, and R274 in the temperature sensitivity reaction, their sensitivity coefficients are relatively small. More reactions involve small molecules, and in terms of sensitivity coefficients, R1 has the largest sensitivity coefficient, while R14, R158, and R212 all have relatively large ones. This indicates that at the high-temperature stage, the reactions involving small molecules control the temperature rise in the fuel system [31]. Figure 7: Temperature sensitivity under different working conditions. From the foregoing analysis, it can be observed that in the low-temperature region, the system reactions are mainly influenced by the reactions of large-molecule fuels; in the high-temperature region, they are affected by the reactions of small molecules; and in the medium-temperature region, they are jointly influenced by the reactions of both types of fuel molecules. Based on the comparison results between the predictions of the ignition delay time with the mechanism in the preceding text and the experimental values, the predicted values of the mechanism in the NTC temperature region are larger, while in the high-temperature region, they are smaller. Therefore, the kinetic parameters of some elementary reactions in the coupling mechanism have been modified. Table 3 below presents the modification of the kinetic parameters of the relevant elementary reactions in the mechanism. In terms of laminar flame speed, the temperature sensitivity analysis method was likewise employed. Figure 8 depicts the temperature sensitivity reactions of the laminar premixed flame under different \(\varphi\). The simulation conditions were three working conditions with \(\varphi\) = 0.8, 1.1, and 1.4, at a temperature of 420 K and P = 0.1 MPa. At \(\varphi\) = 0.8, as depicted in Figure 8a, for the one-dimensional laminar premixed flame, the reaction with the largest temperature sensitivity reaction coefficient is R28: CO + OH = CO\({}_{2}\) + H. This reaction releases a considerable amount of heat and facilitates the generation of H radicals, which is conducive to the augmentation of the laminar flame speed. Among them, R28 and R29 are the identical reactions corresponding to distinct kinetic parameters, jointly governing the oxidation of CO [47]. As depicted in Figure 8b, at \(\varphi\) = 1.1, the reaction with the maximal sensitivity coefficient is R1. Reaction R28 still possesses a relatively large positive sensitivity coefficient, while the sensitivity coefficients of reactions R36, R37, and R175 decline. When \(\varphi\) continues to increase to 1.4, as shown in Figure 8c, the reaction with the greatest sensitivity coefficient is R1. Moreover, the sensitivity coefficients of the other several reactions decrease significantly, contributing less to the temperature increase.