## 3 Results and Discussion  
### Variation of Pressures under the Influence of NSSs  
In the previous studies [31; 32], the overpressures in different devices had been tested to investigate the effects of explosion suppression materials on explosion-suppression. The explosion overpressure \(P_{\text{max}}\) and the rate of pressure rise d\(P\)/dt are the two important explosion parameters, which are significant for damage of gaseous explosion. In current work, the pressure transducer is used to record in-cylinder pressure in CVCB. Figure 4 illustrates the time history of in-cylinder pressures under different initial conditions, namely three different filling densities (21.9 kg/m\({}^{3}\), 38.7 kg/m\({}^{3}\) and 45.1 kg/m\({}^{3}\)) and three different initial pressures (0.2 MPa, 0.3 MPa and 0.4 MPa). The in-cylinder pressure evolution curves are slightly unsmoothed due to existing inherent oscillations. Their sources are combustion noise, mechanical vibration and so on [33]. It is obvious that the pressures change with the same trend in Figure 4. Compared with unfilled CVCB, overpressures are reduced after filling NSSs in CVCB under different initial pressures. It could be explained that the microstructure of NSSs impeded explosion pressure propagation [28; 34]. In CVCB, flame waves pass through surfaces of NSSs, a large amount of energy is absorbed quickly, then the reaction heat is reduced. As illustrated in literature [14], NSSs suppressed explosion reaction, retarded effective energy release. As shown in Figure 4 and Table 3, it is found that overpressures decrease with increasing filling densities of NSSs under different initial pressures, meanwhile the decay rates of overpressures \(Rp_{\text{max}}\) increase with increasing filling densities of NSSs. It also indicates that the suppressing performance increases with increasing the filling density. It can be explained that number of NSSs increase, the contact surfaces are enhanced between the flame and NSSs, thus heat loss increase. It can be explained by [PERSON] [35] that, according to the law of momentum conservation, flame passing through the explosion suppression materials, would cause internal loss and viscosity loss ([PERSON]). \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \(P_{\text{0}}\)/\(\mathbf{Mpa}\) & \(\rho\)/kg/m\({}^{3}\) & \(t_{\text{e}}\)/ms & \(P_{\text{e}}\)/MPa & \(\mathbf{\Phi_{0.e}}\)/MPa/s & \(t_{\text{max}}\)/ms & \(P_{\text{max}}\)/MPa & \(\mathbf{\Phi_{e.max}}\)/MPa/s & \(Rp_{\text{max}}\)/\% \\ \hline \multirow{4}{*}{0.2} & 0 & & & 6.08 & 105 & 0.838 & 6.08 & \\  & 21.9 & 24 & 0.576 & 15.67 & 54.5 & 0.745 & 5.54 & 11.10 \\  & 38.7 & 11.5 & 0.521 & 27.91 & 42.5 & 0.661 & 4.52 & 21.12 \\  & 45.1 & 6.5 & 0.531 & 50.92 & 30.5 & 0.602 & 2.96 & 28.16 \\ \hline \multirow{4}{*}{0.3} & 0 & & & 12.91 & 79.5 & 1.326 & 12.91 & \\  & 21.9 & 17 & 1.005 & 41.47 & 38.5 & 1.173 & 7.81 & 11.54 \\  & 38.7 & 14 & 0.846 & 39 & 33 & 0.943 & 5.11 & 28.88 \\  & 45.1 & 14 & 0.813 & 36.64 & 31.5 & 0.875 & 3.54 & 34.01 \\ \hline \multirow{4}{*}{0.4} & 0 & & & 15.12 & 92 & 1.791 & 15.12 & \\  & 21.9 & 14.5 & 1.067 & 46 & 61.5 & 1.467 & 8.51 & 18.10 \\ \cline{1-1}  & 38.7 & 10.5 & 1.007 & 57.81 & 30.5 & 1.15 & 7.15 & 35.80 \\ \cline{1-1}  & 45.1 & 7.5 & 0.871 & 62.8 & 27.5 & 1.008 & 6.85 & 43.72 \\ \hline \end{tabular}
\end{table} 
Table 3: Experimental results. The decay rates of explosion overpressures \(Rp_{\max}\) and the rates of average pressure rise \(\Phi\) are analyzed to illustrate the effects of NSSs on explosion-suppression, the calculation formulas of \(Rp_{\max}\) and \(\Phi\) are expressed as follows.