## 3 Results
### The Effect of Pressure on the Flame Temperature  
In practical applications of combustion equipment such as gas turbines, pressure is a very important flame influence parameter. Figure 5 plots the flame temperature distribution curves along with the distance at different pressure with and without CO2 dilution. The negative effects of CO2 on the flame temperature at 3 atm and 5 atm behave similarly to that at atmospheric-pressure. The increase in pressure not only causes the combustion zone  
Figure 4: The comparison of the chemical effect and thermal effect on the flame temperature at \(p=1\) atm, \(\alpha_{s}=10\) s\({}^{-1}\), \(\beta=0\)–50%.  
to become narrower, but also improves the maximum flame temperature. The coordinate positions of the flame front without CO2 dilution in 1 atm, 3 atm, and 5 atm are 1.60 cm, 1.5 cm, and 1.47 cm, respectively. The coordinate positions of the flame front with 50% CO2 dilution in 1 atm, 3 atm, and 5 atm are 1.57 cm, 1.42 cm, and 1.36 cm, respectively. By comparing the above coordinate positions of the flame front, the addition of CO2 makes the influence of pressure on the flame front more obvious.  
Figure 6 gives the reduction percentage of the maximum temperature caused by the chemical effect and thermal effect of the CO2 with and without CO2 dilution at different pressures. What can be seen from Figure 6 is that the CO2 dilution causes the peak value of the flame temperature to decrease significantly, whether in ordinary pressure or high pressure (5 atm). More CO2 dilution leads to a greater decrease. The reduction percentage of the flame temperature peak value caused by the chemical effect (\(RP_{chem}\)) declines with the increasing CO2 dilution ratio. However, the reduction percentage of the flame temperature peak value caused by the thermal effect (\(RP_{therm}\)) behaves in the opposite manner to \(RP_{chem}\) which increases with the increasing CO2 dilution ratio. What needs to be specifically pointed out is that Figure 4 shows the decrease value of the flame peak temperature, which shows that it increases with the increase of the CO2 dilution ratio, but that does not mean that it accounts for an increase in the total impact of CO2 on temperature. Figure 6 shows the reduction percentage of the peak temperature caused by the chemical effect and the thermal effect in the total temperature decrease, which can more efficiently reveal the primary and secondary effects and changing trends of chemical effects and thermal effects of CO2 dilution on temperature.  
As a supplement to Figure 6, Figure 7 clearly shows the \(RP_{chem}\) and \(RP_{therm}\) lines with the CO2 dilution ratio in different pressure. At the same CO2 dilution ratio \(\beta\), \(RP_{therm}\) increases with the pressure increase, while the \(RP_{chem}\) behaves in the opposite manner. This means the rise in pressure can promote the thermal effect and reduce the chemical effect in the total effect of the CO2 dilution on the peak of the flame temperature. Corresponding to Figure 6, \(RP_{chem}\) and the \(RP_{therm}\) have different performances on the increase of CO2 dilution ratio; that is, the former decreases, while the latter increases.  
Figure 5: The effect of CO2 on the flame temperature at different pressure (1–5 atm); \(\alpha_{s}=10\) s\({}^{-1}\); \(\beta=0\%,50\%\).  
Figure 6: The comparison of the chemical effect and thermal effect on the maximum flame temperature with different pressure at \(\alpha_{s}=10\) s\({}^{-1}\), \(\beta=0\)–50%.