Condensed Combustion Products Characteristics of HTPB/AP/Al Propellants under Solid Rocket Motor Conditions
Round 1
Reviewer 1 Report
The concept of the study is inaccurately formulated and the scientific novelty of this study is not shown.
The processes of agglomeration of aluminum during combustion of (HTPB/AP/Al) composite propellants have been studied in sufficient detail previously and the presented results do not add anything new.
For example, the phenomenon of average particle size decrease of condensed combustion products, observed under a higher chamber pressure, were studied earlier.
In addition, (HTPB/AP/Al) composite propellants cannot be considered as promising propellants.
Taking into account the current trends in the creation of promising composite solid rocket propellants, this study could have been of value 20 years ago.
A related detailed studies is presented in the papers that should be included in the References:
- L.T. DeLuca, L. Galfetti, F. Maggi, G. Colombo, A. Bandera, S. Cerri, and P. Donegà, Burning of metallized composite solid rocket propellants: Toward nanometric fuel size,
ESA Space Propulsion 2008: 2nd International Symposium on Propulsion for Space Transportation, At: Heraklion, Crete, Greece, 05-08 May 08, Volume: Session No. 5 "Solid Rocket Motors", Paper 42-242, pp. 1-10
- L.T. DeLuca, F. Maggi, S. Dossi, V. Weiser, A. Franzin, V. Gettwert, and T. Heintz, High-energy metal fuels for rocket propulsion: characterization and performance, Huozhayao Xuebao/Chinese Journal of Explosives and Propellants 2013(6):1-14
- Fukuchi A.B., Effect of aluminum particle size on agglomeration size and burning rate of composite propellant, Journal of Thermal Science and Technology, 2022, Volume 17, Issue 1, 21-00346,
https://doi.org/10.1299/jtst.21-00346
There is a long-standing inconclusive dispute among specialists-designers of composite solid rocket propellants about the role and importance of metal components in solid propellant compositions. However, the use of metal/metal oxide additives in propellant compositions has several known disadvantages, including that the propellant composition becomes more sensitive to accidental initiation due to impact, friction, spark, flame or heat; condensed solid metal particles in the combustion products have a devastating effect on the structural elements of the propulsion
system due to abrasive action; the process of combustion of metals leads to the appearance of toxic combustion products.
One of the ways to improve the energy and ballistic properties of promising rocket propellants is the use of ultrafine metals in modern compositions. However, by raising the combustion temperature of propellants and
reducing the mass of the gaseous working fluid, metals form an inefficient c-phase. The presence of metallic fuel in the composition of solid rocket propellants leads to losses in the specific impulse of the propellant, and
a number of modifiers and stabilizers reduce its density.
The most important direction for further improving the energy and ballistic properties of promising solid rocket propellants is the use of nano-dispersed components in modern compositions, which involves the creation of high-energy compositions with improved characteristics.
The general advantage of using nano-sized components is their high reactivity. Due to extremely large specific surfaces, nano-sized components are able to have a significant effect simultaneously in the condensed and gas phases: increase the rate of decomposition and combustion, change the thermal conductivity and increase the rate of heat release in the reaction zones; change the size of the reaction zones, the mechanisms of the reactions. As a result, based on traditional compositions of solid propellants, new compositions with significantly improved characteristics of environmental safety, combustion, detonation and energy efficiency can be created.
Numerous recent experimental studies have shown that carbon-based functionalized nanostructures have a significant impact on the thermal decomposition, ignition, combustion, and chemical properties of solid propellants and have the potential to significantly improve their combustion characteristics, thermal stability, and environmental safety.
In particular, previous experimental studies have shown that the addition of graphene-based nanomaterials to the composition of the solid propellant makes it possible to increase the burning rate by 8–10 times, which is of
fundamental importance for the development of propulsion systems for advanced aerospace systems.
In connection with the foregoing, the authors are recommended to more accurately formulate the concept and scientific novelty of their research in the paper.
It is also necessary to formulate new directions for improving composite solid rocket propellants, which follow from the provided study.
Comments for author File: 
Comments.pdf
Author Response
Thank you for your comments. We agree with the reviewer that the Introduction of the original manuscript of our paper does not express the concept and scientific novelty of the research more accurately. The processes of aluminum agglomeration during the combustion of HTPB/AP/Al composite propellants were studied in sufficient detail previously by many researchers, including the three articles recommended by Reviewer. We really appreciate the content and conclusion of these studies, and cited them in the article. Combined with the problem of not outstanding the concept and scientific novelty, the Introduction was strengthened and marked in red. In this study, the novelty CCPs collection system is built, which can provide the same combustion condition as the real rocket, and the analysis of all CCPs of propellant combustion can better reflect the combustion situation of aluminized propellant in the real rocket motors. We support the reviewer’s comment that HTPB/AP/Al composite propellants cannot be considered as promising propellants because of several known disadvantages caused by aluminum agglomeration. However, HTPB/AP/Al composite propellants are typical and widely used in solid rocket motors. Therefore, HTPB/AP/Al composite propellant were selected as the research objects in this manuscript. We appreciate it very much for this good suggestion that it is also important to formulate new directions for improving composite solid rocket propellants according the provided study. According to the results of the provided study on the influence of CCPs particle size and Al combustion efficiency, we have formulated the improvement direction of the aluminized composite propellant, and strengthened the conclusion.
Author Response File: Author Response.pdf
Reviewer 2 Report
his paper describes an experimental campaign carried out with a homemade test bench made to characterize the solid residue of the combustion of a grain of propellant of the class HTPB/AP/Al
Although well organized and written (I suggest to the authors a revision for English and to simplify some periods "difficult to read") in my opinion, the article has some critical issues that I would like to be discussed / commented on by the authors and possibly integrated into the article
First of all, there is a vast, enormous literature concerning the combustion of aluminum in solid propellants; starting from the combustion near the surface to finish with the phenomenon of "distributed combustion" (ie the combustion of agglomerates during their evolution in the combustion chamber). In the latter case it is evident that the characteristic times in the chamber play a very important role in the evolution of the fluid dynamic field and in the dimensions of the particulate that faces the throat section of the nozzle.
A first question that arises is related to the experimental apparatus: how can the authors guarantee that the characteristic times of the phenomena that occur in the experimental apparatus are representative of what really happens in an ordinary combustion chamber of a rocket?
The second question concerns the nature of the information obtained from the results: how does the developed work add elements of novelty compared to what has been produced to date and present in the literature? The doubt also arises for the small number of references presented which I suggest to integrate with other literature
third question: the quality of the work is also linked to the precision of the measurements and the repeatability of the experiments. I suggest that the authors comment on this as well
To conclude: the figures are of good quality but, in my opinion, they should be commented a little better (ie fig 6,8 and 11); a list of symbols may also be useful
Author Response
Point 1： How can the authors guarantee that the characteristic times of the phenomena that occur in the experimental apparatus are representative of what really happens in an ordinary combustion chamber of a rocket?
Response 1: Thank you for your comments. The combustion chamber of the apparatus in this work has the same structure as that of the ordinary solid rocket, and gas phase combustion products could rapidly cool down and cool CCPs after sudden expansion, when combustion products are ejected from the combustion chamber. Therefore, it could be guaranteed that the characteristic times of the phenomena that occur in the experimental apparatus are representative of what really happens in the ordinary combustion chamber of rocket motors.
Point 2: How does the developed work add elements of novelty compared to what has been produced to date and present in the literature? The doubt also arises for the small number of references presented which I suggest to integrate with other literature.
Response 2: Thank you for your suggestion. We support the reviewer’s comment that the elements of novelty are not particularly prominent and the number of references presented is small. We have carefully studied more research work related to the combustion mechanism of HTPB/AP/Al propellants. We really appreciate these reaearch and have included them in the References. In this study, the novelty CCPs collection system was built, which can provide the same combustion condition as the real rocket, and the analysis of all CCPs of propellant combustion can better reflect the combustion situation of aluminized propellant in the real rocket. In order to highlight these novel elements in the revised manuscript, the sections of Introduction and Conclusion are strengthened and marked in red.
Point 3: The quality of the work is also linked to the precision of the measurements and the repeatability of the experiments. I suggest that the authors comment on this as well.
Response 3: Thank you for your advice. We apologize for neglecting to comment on the precision of the measurements and the repeatability of the experiments. Reproducibility experiments were performed for laser particle size analysis and complexometric titration, and the relative error of measurement results are provided in Figs 6, 9, 11 and Tables 4, 5, 6. Relevant comments are also provided below the corresponding Figures and Tables.
Point 4: The figures are of good quality but, in my opinion, they should be commented a little better (ie fig 6,8 and 11); a list of symbols may also be useful.
Response 2: Thank you for your suggestion. It is true that Figures 6, 8 and 11 are not better commented. We carefully analyzed the data in Figures. 6, 8 and 11, and supplied detailed explanations, which are replenished and marked in red in the revised manuscript. The list of symbols is also replenished and maket in red.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
A revised manuscript looks much better.
However, I suggest including into the Introduction and Conclusion sections information regarding scientific novelty of the obtained results in comparison with the previous research.
In particular, what new features of the propellant combustion mechanism, in comparison with previous research, can be identified using the developed experimental setup?
Whether a developed experimental setup can provide increased selective sensitivity to the specific collected substances from the condensed combustion products?
The inclusion of such information is necessary to attract the attention of potential readers of your paper.
Thank you!
Comments for author File: Comments.pdf
Author Response
Point : I suggest including into the Introduction and Conclusion sections information regarding scientific novelty of the obtained results in comparison with the previous research. In particular, what new features of the propellant combustion mechanism, in comparison with previous research, can be identified using the developed experimental setup? Whether a developed experimental setup can provide increased selective sensitivity to the specific collected substances from the condensed combustion products?
Response : Thank you for your suggestion. We support the reviewer’s comment that the scientific novelty the obtained results are not particularly prominent. All CCPs generated by propellant combustion were collected in situ under the same conditions as the solid rocket motor combustion chamber by the established experimental system, and the morphology, particle size and composition of CCPS were characterized. On this basis, the influence of aluminum agglomeration during propellant combustion on both the particle size distribution of CCPs and the combustion efficiency of aluminum was revealed. We apologize for not explaining the selectivity of CCPs clearly, and infact all of the measurements were for all the CCPs collected, in this study. In order to highlight the scientific novelty of the obtained results in the revised manuscript, the sections of Introduction and Conclusion are strengthened and marked in red.
Author Response File: Author Response.pdf
