Round 1

Reviewer 1 Report

This work compares the ignition and combustion of different types of propellants using different ignition systems. This topic is very interesting. However, at the beginning, I was planning to reject the paper because it is a technical report more than a research article. But, since I think that these experimental results deserve to be published, I think that authors can make the effort to rewrite the paper in depth.

There are only 11 references, minus 4 if we exclude auto-citation, that is not enough for a research article. Several references can be added completing the introduction and comparing obtained results with existing literature. For instance, different ignition systems can be presented in introduction, showing recent works on conventional, electrical, laser ignition of gun propellants (there are plenty of them) and presenting the main conclusions. The idea is to situate present work in the literature (not performed in the present form).

Line 52: this gunpowder mass must be given to make the experiments reproducible.

By the way, what is the mass of propellant used in experiments?

Each experiment is performed one time for given conditions or duplicate, maybe triplicate?

Line 58: which pressure? Experimental?

Table 2: what are GP and PL?

It is likely that minimum ignition energies of the three studied propellants are very different. Is it logical to use the same energy to ignite the three? This MIE should be given as there is a comment on used energy line 110.

It looks like the only measured signal is pressure as function of time. With such signals, other data can be obtained (ignition time, maybe rate of spread). Experimental data should be better used.

Line 120: what are these coefficients?

Figure 3: how are obtained the different shape functions?

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 2 Report

Review: Analysis of Application of Plasma Ignition in Closed Vessel Tests

General comment: The article is clear and to the point. The introduction exposes a brief overview of the subject but need to be enhanced. The study presents the effects of the ignition method on the ballistic properties of three types of propellants via closed vessel experiments. Authors conclude that ignition method may influence propellant characteristic and that plasma ignition does not eliminate differences between theoretical and experiments shape function for SB and LOVA propellants.

Comment #1: The introduction is too brief and need to be extended. Authors can introduce energetic materials and their general purpose. Also authors can briefly describe other experiments related to EM or propellants such as thermal stability, ageing, laser ignition ... (e.g. in MDPI journals: https://doi.org/10.3390/nano10112222 - https://doi.org/10.3390/ma11112236  - https://doi.org/10.3390/molecules25102276 - https://doi.org/10.3390/polym11121966) in order to have a good overview of the EM field.

Comment #2: Line 49 “Details of experimental procedure were described in [9]”. Authors need to describe at least with a short paragraph this procedure for readers.

Comment #3: Line 52 “The mass of the gunpowder igniter was adjusted to ensure that the nominal value of ignition pressure was the same in all tests”. Authors need to indicate also here the nominal pressure of 3.16 MPa.

Comment #4: Line 54 “3.84 kJ”. How was this value chosen? Did authors consider to test higher values?

Comment #5: Table 1. Propellants compositions are missing, especially for the LOVA propellant.  

Comment #6: Line 63 “So, the values of f and η were also calculated for the ignition pressure pi equal to zero. The determined values of f and η are given in Table 2 (values in parenthesis correspond to pi = 0).” Authors need to comment these calculated values.

Comment #7: Table 2. Authors need to correct the last column as “η [dm3/kg] (PL)”.

Comment #8: Line 68 “The method of reduction of closed vessel tests results was described in [9]”. Just quoting the reference is not enough. Author need to give more information on this method.  

Comment #9: Line 79 “However, they diverge at 0.1 MPa”. Authors might add another figure to point out this phenomenon.  

Comment #10: Line 101 “This effect is not observed in the case of ignition of the single-base propellant. It can be explained by the large value of the specific surface area As of this propellant (see Table 1)”. Is it a common fact that specific area have a higher value for SB than DB or LOVA propellants? Or is it the manufacture procedure (e.g. extrusion pressure) that impacts this parameter?

Comment #11: Line 138 “Grains of single-base and LOVA propellants have a tendency to brittle crush, that increases the burning surface in the first phase of burning and diminishes it in the second phase”. Authors might indicate another references than [11] for this explanation either for the SB, LOVA or both propellants.

Comment #12: This paper should still be considered for publication after consideration of the above comments.

Author Response

Please see the attachment

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Authors made good effort to improve the paper. However, I still think that this article is more a technical report than a research paper. This is confirmed by the introduction where authors say that the methodology was already published, and applied in the present paper to other materials…

Experimental results could be better analyzed and discussed (and compared to existing literature).

Minor comments

Authors increased artificially the numbers of references ([4-20] for a single sentence in the introduction, without saying what was performed in the papers seems excessive).

Experimental section: much improved compared to previous version but experiments are still not reproducible since composition of propellants are not given (just for LOVA in a Table caption).

Author Response

Remark 1

Authors made good effort to improve the paper. However, I still think that this article is more a technical report than a research paper. This is confirmed by the introduction where authors say that the methodology was already published, and applied in the present paper to other material.

Response

The assessment of applicability of the plasma jet ignition in closed vessel tests is the objective of our paper. So, our work is not a fundamental research aimed at getting insight into the physical processes taking part in an investigated system but it is aimed on a practical problem. We suppose that this is a reason of the Reviewer’s doubts concerning the scientific merit of our work.

We have found in the literature very few works making a comparison between the gunpowder ignition and the plasma jet ignition. Results of investigations presented in those works do not give an answer to the question “is it worthwhile to replace the classical gunpowder ignition by the plasma jet ignition in closed vessel tests”? The plasma jet ignition is not an easy technique in comparison to the gunpowder ignition. But there are some advantages of this technique. In particular it causes that the assumption of the simultaneous ignition of all grains of tested propellant is better fulfilled than in the case of the gunpowder ignition. This is an important assumption, because methods of analyzing closed vessel tests results are based on it. That is why we decided to get a broader material for making the comparison of the two methods of ignition and the paper presents it. We think that results of the comparison may be of interest for researchers dealing with gun propellants. “Energies” publishes works that are aimed on some practical issues.

We think that we might have not given a clear description of our aims in the Introduction. So, we have tried to explain them better in the modified version of our paper.

Remark 2

Experimental results could be better analyzed and discussed (and compared to existing literature).

Response

We considered adding an analysis of the influence of the method of ignition on the ignition delay. We done such an analysis in our earlier work for a single-base propellant. We came to the conclusion that much more informative is the comparison of experimental shape functions determined for the two methods of ignition.

Although results of application of the plasma jet ignition were subjects of many publications; there are very few papers that present results of investigations comparable to our work. They present only selected results, for example pressure time courses, the dependence of the burning rate on pressure values. We have modified the Introduction and we have given information concerning these papers.

In our paper we analyze all data that are determined in closed vessel tests and used in interior ballistics calculations. In the section Results and Discussion we have added two remarks concerning comparison with accessible literature data. We have not been able to compare the experimental shape function plots because this function in used only by our team.

Remark 3

Authors increased artificially the numbers of references ([4-20] for a single sentence in the introduction, without saying what was performed in the papers seems excessive).

Response

We understood one of the earlier Reviewer’s remark as we are not conscious of the broad literature in the field of propellant ignition. That is why we increase the number references. We agree that it may look like artificial. That is why we have added in the Introduction a review of selected references closely related to our work.

Remark 4

Experimental section: much improved compared to previous version but experiments are still not reproducible since composition of propellants are not given (just for LOVA in a Table caption)

Response

We have added more detailed information concerning compositions of propellants.

Round 3

Reviewer 1 Report

Authors answered all my questions, I think the paper can now be published.

I really appreciated authors’ answer to my Remark 1.

I still have 4 minor comments that should be taken into account by the authors before publication, but I don’t need to review another version of the paper.

- l. 31 “augmented combustion” should be reworded as the meaning is not clear.

- l. 85-86 the sentence should be rephrased since it is not grammatically correct.

- l.100 and therefore, what is this reproducibility?

- l. 257 underlined