## 3 Results and Analysis
### Combustion Characteristics  
To analyse the effect of the pore structure on combustion performance caused by low-temperature decomposition of AP, a test was carried out using a homemade 13 mL closed bomb. The schematic diagram of the test system of the closed bomb is shown in Figure 10; the pressure sensor was a PCB113b22, with a range of 34.5 MPa and a frequency of 30 MHz. The test system adopts a pressure trigger, and the threshold is 0.5 MPa; the pressure data for 2.1 ms before trigger and 30 ms after trigger were recorded. The variation in combustion pressure over time in the binary system of porous AP (ordinary AP) and Al (median particle diameter of 10 \(\upmu\)m) in a confined space was studied, as shown in Table 3. The effect of the pore structure on the burning rate performance was also analysed. Three tests were repeated for each proportion with a dose of 54 mg.  
The experimentally derived pressure-time curve is shown in Figure 11, and after replacing the ordinary AP with porous AP, the P-t curve peak becomes increasingly steeper. When the ratio of porous AP to Al was 80:20, the pressure change was abrupt after ignition, forming a typical shock wave curve, which can be considered an explosion.  
Figure 12 shows the relationship between the rate of pressure variation, dP/dt, and pressure, P, with Table 4 showing the peak pressure, peak time and rate of change in peak pressure under different conditions. dP/dt increases significantly when using porous AP instead of normal AP, demonstrating that porous AP can lead to a higher combustion rate, aggravating the reaction intensity and accelerating the combustion speed. The time to reach the peak was shortened, with the peak becoming higher during combustion. When the ratio of AP and Al was 80:20 the pressure peak had increased 2.7 times, with the maximum rate of change in pressure increasing 34 times. Therefore, the degree of reaction was significantly intensified. This is because the porous structure formed by partial decomposition of AP has a larger specific surface area. The porous structure of AP tends to lead to convective combustion to accelerate the combustion rate. When the proportion of porous AP reaches 80%, the combustion is transformed into an explosion.  
Figure 10: P–t curve for different AP:Al proportions.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Number** & **AP** & **AP/Al** & **Number of Replicates** \\ \hline
1 & & 50:50 & 3 \\
2 & Ordinary AP & 70:30 & 3 \\
3 & & 80:20 & 3 \\
4 & & 50:50 & 3 \\
5 & Porous AP & 70:30 & 3 \\
6 & & 80:20 & 3 \\ \hline \hline \end{tabular}
\end{table}
Table 3: The test scheme for the closed bomb.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Number**} & \multirow{2}{*}{**AP**} & \multirow{2}{*}{**AP:Al**} & \multicolumn{2}{c}{**Peak**} & \multicolumn{2}{c}{**Peak of**} \\  & & & **Pressure/MPa** & **Time/ms** & **dP/dt** \\ \hline
1 & & 50:50 & 1.17 & 5.74 & 264 \\
2 & Ordinary & 70:30 & 1.76 & 3.39 & 1576 \\
3 & & 80:20 & 1.34 & 4.76 & 714 \\
4 & & 50:50 & 2.06 & 3.34 & 2335 \\
5 & Porous & 70:30 & 3.15 & 2.30 & 12,390 \\
6 & & 80:20 & 3.64 & 2.16 & 24,540 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Combustion characteristics of the AP-Al closed bomb for different AP:Al proportions.  
Figure 11: P–t curve for different AP:Al proportions.