Study on the Variation Laws and Fractal Characteristics of Acoustic Emission during Coal Spontaneous Combustion

Round 1

Reviewer 1 Report

I think this is a very standard academic paper with a more rigorous thinking. According to my professional orientation, I have no very specific opinions. Therefore, I propose to accept it in its current state. Of course, the editor needs to refer to the suggestions of other reviewers.

Author Response

Response to Reviewer 1 Comments

I think this is a very standard academic paper with a more rigorous thinking. According to my professional orientation, I have no very specific opinions. Therefore, I propose to accept it in its current state. Of course, the editor needs to refer to the suggestions of other reviewers.

Response: Thank you for your recognition of our research and once again, thank you for your comments.

Reviewer 2 Report

This paper tests and studies the change of acoustic emission signal during coal spontaneous combustion and performs fractal analysis, which provides a theoretical basis for realizing the monitoring and early warning of coal spontaneous combustion, which is an interesting and meaningful research topic and writing. Therefore, I recommend this paper for publication after minor revision.

1. The introduction section needs further condensation.

2. Why bituminous coal was chosen for the selection of coal sample, please provide a brief analysis of the coal sample.

3. Some references are not new enough, for example: Deng, J., Xu, J.C., 1999. Chin. j. Journal of Xi'an Mining Institute, 4: 293-297+337. It is suggested to revise it to the studies on acoustic emission in recent years. Summary of natural coal fire forecasting technology at home and abroad should be expounded.

4. The labels of the figures should be unified, for example, Figure 3, FIG. 3 and Fig. 3 are used confusingly. 5.

5. The discussion section is relatively simple. Only the low-temperature nitrogen adsorption and acoustic emission fractal parts are discussed.

6. Please explain the meaning of "DT", which it first appears in the summary of 2.1.

Author Response

Thank you for your comments. Based on your comments, we have revised the original text and the issues raised. We have also included a revision note after the end of the marked-up manuscript, and the marked-up manuscript and revision note are attached.

Author Response File: Author Response.pdf

Reviewer 3 Report

This work conducted a series of large-scale spontaneous combustion and heating experiments of coal under different temperature conditions. The AE technique was used to monitor the spontaneous combustion processes and the AE characteristics were correlated with the failure behaviors. I believe the readers will be interested in the topic and experimental results of this paper. However, before publication, following shortages must be overcomed.

1.      There are many grammar and typo errors in the manuscript. Please find someone fluent in English to read your manuscript and make suggestions for improvement.

2.      Some background on the application of AE technique on failure process of coal are listed, leading to a very long Introduction. Moreover, a description of shortcomings and improvements in different investigations is missing.

3.      Please specify the novelty of this investigation at the end of the Introduction.

4.      The variables in Table 1 need an explanation, either in Table captions or in the text.

5.      In the experimental part, it is necessary to provide the operating frequency range of the AE sensor and the preset threshold value for eliminating noises.

6.      In Figures 2-3, what is the criterion for identifying the three stages? It is important to clarify the classification criterion.

7.      In Figures 4-5, why the authors only provided the AE behavior before 600 s instead of the whole failure process? Also, please clearly indicate which data points are count and cumulative count in the figures.

8.      In Figure 7, it is necessary to provide a detailed caption for each graph.

9.      Missing unit of average frequency in Figure 8.

10.   In Line 359, what do you mean by “the main frequency of the acoustic emission signals”? In Line 338, why only 8 AE signals under each temperature condition are selected for showing the frequency characteristics?

11.   The authors tried to correlate the frequency characteristics of AE signals with different temperature conditions, which is very important because the information related to damage mode are generally encoded with the frequency domain of AE waveforms. However, it is really hard for me, and maybe for readers, to understand the single-peak high/low frequency, and bimodal high/low frequency, which are too qualitative. I recommend the authors explore the variations of peak frequency and centroid frequency with respect to failure time, and then provide a statistical result of peak frequency/centroid frequency under each temperature condition. I suggest the authors refer to the following papers which correlate the frequency characteristics of all AE signals with different failure processes.

https://doi.org/10.1016/j.ijfatigue.2022.106860

https://doi.org/10.1016/j.jmapro.2022.01.012

12.   In Line 543, the authors claimed that “acoustic emission signal in the process of heating and heating of the coal body comes from the generation of the pore structure”. Can you provide some images showing the pore structures of coal under different temperatures and support your conclusion?

Author Response

Thank you for your comments. Based on your comments, we have revised the original text and the issues raised. We have also included a revision note after the end of the marked-up manuscript, and the marked-up manuscript and revision note are attached.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

After revision, the present manuscript can be accepted by the journal.