NEPE propellant is the third generation solid propellant, and its energy is currently the highest among solid propellants. In NEPE propellants, PEG is instead of nitrocellulose as the binder, mixed with liquid nitrate ester as the plasticizer, and composed of solid components such as RDX (or HMX), AP, and Al powder. Due to its full utilization of the high energy of liquid energetic nitrate ester plasticizers and the excellent low-temperature mechanical properties of polyether polyurethane, as well as the use of a large number of high-energy explosives as solid components, its energy and mechanical properties are both excellent. It breaks through the theoretical specific impulse limit of 2636N·s/kg and increases the density specific impulse by 5~10%. It has been successfully applied in new generation strategic missiles such as the Trident IID5 submarine launched missile in the United States. From Table 5 and Figure 6, it can be seen that when 40wt.% RDX or HMX has been added, the theoretical specific impulse the NEPE propellant has reached 2639.8N·s/kg and 2638.6N·s/kg, respectively. Interestingly, the standard specific impulse of NEPE propellant added CL-20 is 2635.4N·s/kg, slightly lower than that of NPEP-RDX and NEPE-HMX. The standard specific impulse of NEPE-TKX-50 is only 2621.5N·s/kg, which is the lowest energy of the propellant formula in Table 5. But when DAP-4 is added, the energy performances increase linearly. Among them, the propellant (NEPE-5) that completely uses DAP-4 as a solid filler has a standard specific impulse of up to 2898.3N·s/kg, which is the highest propellant specific impulse in this article. This specific impulse is even higher than some liquid propellants, such as N2O4-UDMH propellant (o/f=2.57, Pc=70atm, Pe=1atm, T0=298K, Isp=2813.2N·s/kg). This is a huge advancement for solid rocket technology. In addition, it can be seen from Figure 6 that for NEPE propellants, when DAP-4 is added, the combustion temperature increases linearly and the average molecular weight of the combustion products decreases linearly. Moreover, in NEPE propellant, when the mass fraction of DAP-4 is constant, the energy performances of NEPE-RDX, NEPE-HMX, NEPE-CL-20, and NEPE-TKX-50 are similar.
Table 5 Energy performance of NEPE propellants added DAP-4
Codes
|
Propellant Formulas
|
Isp
(N·s/kg)
|
C*
(m/s)
|
Tc
(K)
|
Mc
(g/mol)
|
NEPE-1
|
PEG8%/NG3.5%/BTTN3.5%/Al15%/AP30%/RDX40%
|
2639.8
|
1615.6
|
3628.3
|
28.587
|
NEPE-2
|
PEG8%/NG3.5%/BTTN3.5%/Al15%/AP30%/RDX30%/DAP-410%
|
2709.1
|
1655.3
|
3729.7
|
28.076
|
NEPE-3
|
PEG8%/NG3.5%/BTTN3.5%/Al15%/AP30%/RDX20%/DAP-420%
|
2776.9
|
1691.9
|
3814.7
|
27.547
|
NEPE-4
|
PEG8%/NG3.5%/BTTN3.5%/Al15%/AP30%/RDX10%/DAP-430%
|
2839.7
|
1726.2
|
3886.9
|
27.011
|
NEPE-5
|
PEG8%/NG3.5%/BTTN3.5%/Al15%/AP30%/DAP-440%
|
2898.3
|
1758.5
|
3949.1
|
26.476
|
NEPE-6
|
PEG8%/NG3.5%/BTTN3.5%/Al15%/AP30%/HMX40%
|
2638.6
|
1614.9
|
3626.2
|
28.593
|
NEPE-7
|
PEG8%/NG3.5%/BTTN3.5%/Al15%/AP30%/HMX30%/DAP-410%
|
2708.2
|
1654.8
|
3728.3
|
28.081
|
NEPE-8
|
PEG8%/NG3.5%/BTTN3.5%/Al15%/AP30%/HMX20%/DAP-420%
|
2776.4
|
1691.6
|
3813.9
|
27.551
|
NEPE-9
|
PEG8%/NG3.5%/BTTN3.5%/Al15%/AP30%/HMX10%/DAP-430%
|
2839.5
|
1726.0
|
3886.6
|
27.013
|
NEPE-5
|
PEG8%/NG3.5%/BTTN3.5%/Al15%/AP30%/DAP-440%
|
2898.3
|
1758.5
|
3949.1
|
26.476
|
NEPE-10
|
PEG8%/NG3.5%/BTTN3.5%/Al15%/AP30%/CL-2040%
|
2635.4
|
1606.2
|
3783.4
|
30.294
|
NEPE-11
|
PEG8%/NG3.5%/BTTN3.5%/Al15%/AP30%/CL-2030%/DAP-410%
|
2705.2
|
1646.6
|
3835.8
|
29.259
|
NEPE-12
|
PEG8%/NG3.5%/BTTN3.5%/Al15%/AP30%/CL-2020%/DAP-420%
|
2772.1
|
1685.3
|
3879.8
|
28.278
|
NEPE-13
|
PEG8%/NG3.5%/BTTN3.5%/Al15%/AP30%/CL-2010%/DAP-430%
|
2836.4
|
1722.5
|
3917.1
|
27.351
|
NEPE-5
|
PEG8%/NG3.5%/BTTN3.5%/Al15%/AP30%/DAP-440%
|
2898.3
|
1758.5
|
3949.1
|
26.476
|
NEPE-14
|
PEG8%/NG3.5%/BTTN3.5%/Al15%/AP30%/TKX-5040%
|
2621.5
|
1609.4
|
3439.7
|
27.101
|
NEPE-15
|
PEG8%/NG3.5%/BTTN3.5%/Al15%/AP30%/TKX-5030%/DAP-410%
|
2700.6
|
1655.1
|
3606.4
|
27.039
|
NEPE-16
|
PEG8%/NG3.5%/BTTN3.5%/Al15%/AP30%/TKX-5020%/DAP-420%
|
2771.6
|
1694.0
|
3742.3
|
26.903
|
NEPE-17
|
PEG8%/NG3.5%/BTTN3.5%/Al15%/AP30%/TKX-5010%/DAP-430%
|
2839.2
|
1728.0
|
3854.7
|
26.711
|
NEPE-5
|
PEG8%/NG3.5%/BTTN3.5%/Al15%/AP30%/DAP-440%
|
2898.3
|
1758.5
|
3949.1
|
26.476
|
The changes in energy performance after replacing high-energy explosives with DAP-4 in different propellant systems were compared earlier. A comparison of the energy performance of four types of propellants is investigated, namely HTPB-5, GAP-5, CMDB-5, and NEPE-5, without RDX, HMX, CL-20, and TKX-50, but only with DAP-4. From Figure 7, it can be seen that among the four kinds of propellants, HTPB-5 has the lowest standard specific impulse, characteristic velocity, and combustion temperature, but its average molecular weight of combustion products is also the lowest. So, the advantage of HTPB-5 propellant is that it produces a large amount of gas during the combustion process, but lacks sufficient combustion heat. From Figure 8 (a), it can be seen that the combustion products of HTPB-5 contain a large amount of H2 and CO, without the generation of H2O and CO2. This is the reason why the combustion temperature is not high but the average molecular weight of the combustion products is very low, indicating that the oxygen balance of this formula is too low. The energy performance of GAP-5 is higher than HTPB-5, but lower than CMDB-5 and NEPE-5. Figure 8 (b) shows that the molar ratios of CO2, CO, H2O, and H2 in its combustion products are relatively balanced, and a large amount of N2 is also generated. The standard specific impulse and characteristic velocity of CMDB-5 are higher than HTPB-5 and GAP-5, but lower than NEPE-5. Due to the abundant oxygen in the CMDB-5 formula, its combustion temperature is relatively high, and the corresponding combustion products contain a large amount of CO2 and H2O. At the same time, the content of H2, CO, and N2 is also high, indicating that the oxygen balance of CMDB-5 is relatively moderate. Figure 7 shows that the NEPE-5 propellant has the highest energy, and its standard specific impulse and characteristic velocity are higher than the other three types of propellants. Figure 8 (d) shows that its combustion products contain a large amount of CO, H2, and N2, as well as an appropriate amount of CO2 and H2O generation, which is a typical feature of high-energy propellants. Although the horizontal comparison of the four propellants in this article does not provide an absolute explanation, the research results still show a trend that missiles using NEPE propellants have the advantages of high density, high energy, long range, and small volume. Therefore, development of NEPE propellants is an important direction for the development of solid propellants.