Experimental Study on the Pulsed Operating Characteristics of a Hydrogen–Oxygen Engine Based on Microwave Ignition Technology
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe experiments present in this work are interesting and valuable. However, the analysis of the experimental results is weak. The authors should carefully revise their manuscript, as there are too many typos, grammatical errors and formatting issues in current version.
- Page 2. Sentences before reference [12] are repeated.
- Some statements seem contradictory and confusing. For example “Current microwave ignition technology is immature” and “Microwave ignition has proven to be an excellent and promising technology”
- Abbreviation should be explained at its first occurrence. For example the “TEM waves”.
- Page 4. Electric field simulation using COMSOL is mentioned. Yet, no results were given here.
- Figure 2 was mentioned in section 2.1. while it was placed in section 2.2.
- Figure 3 could be improved by replacing it with a schematic diagram. Current pictures appear cluttered and lack clarity.
- Figure reference should be carefully checked. “Error! Reference source not found.”
- Figure description should appear before the figure itself.
- Figure 4 presents the complete work process at the thruster nozzle. Time information should be provided for each picture. Besides, the first row of figure 4 contain almost no information. Resolution of this figure is low and should be improved by rescaling.
- What is the measurement frequency of the pressure sensors?
- Figures 7, 9, and 11 are suggested to include time labels and be rescaled to a proper size.
- The authors mentioned that “the outer region of the flame”, in figure 11, “is a distinct light blue color”. However, the color of the flame could hardly be distinguished in the figure.
- What are the combustion efficiencies under the test conditions?
- Advantages of in-situ utilization of the water resources are not the conclusion of this work. And the second and third paragraphs are also not the conclusions from current research.
Author Response
Thank you very much for your suggestion, we have corrected the content of the paper, here is my response to your suggestion.
About comments 3, 5 and 8, they are problems with the layout of our thesis, thank you for your correction, and they have been corrected now.
About comment 1, it was a problem when we translated the paper, and now we have rewritten this paragraph.
About comment 2, it says that the research is immature, but it has potential, so it is worth researching. Maybe there was a problem in my translation that made you have ambiguity, I replaced 'potential' with 'capacity'. '.
About comment 4, the shape of the antenna head was finalized by analyzing the electric field. In the original version, it was divided into two paragraphs, which made the content read like a split, and it has been revised now.
About comment 6, the entire experimental system has a little too much equipment, but it is labeled with its name. There is no useless clutter, if you still think it's too messy, I can go back to the lab and take a new one.
About comment 7, we were not strict enough in our own checking, and only the first few photos were cross-referenced, but now we have inserted cross-references in all photos and references.
About comment 9, this burn was more faint and the flame image was indeed darker throughout. In the early part of this burn, the flames are not yet fully present, so the flame image in the first row is almost black, which is the correct display, not because of the lack of resolution of the figure.
About comment 10, the parameters of the individual measuring instruments have been added, including the measurement frequency of the pressure sensor in line 236.
About comment 11, since the flame image was indeed too dark, we have corrected it by presenting it in a different way, with a superimposed image of the flame image and a contour map of the flame image, with the chronological order of the individual contours in the contour map.
About comment 12, since the flame image is indeed too dark, we have corrected it by changing the presentation to an overlay of the flame image and an outline of the flame image, and the text description of this part has also been corrected.
About comment 13, it is well known that combustion efficiency is generally defined as the ratio of the actual energy released during combustion of fuel and oxidizer to the theoretical maximum possible energy released. The hydrogen and oxygen used in this paper are generated by a water electrolysis module, stabilized by a small stabilizer tank and then passed into the combustion chamber. However, the specificity of the microwave ignition used in the thruster of this paper, the igniter ionizes the oxygen to form a plasma torch before entering the combustion chamber to ignite the hydrogen. The plasma has a promoting effect on combustion, which is different from the chemical reaction under ordinary hydrogen-oxygen electric ignition, and it is difficult to arrange thermocouples to measure the temperature due to the presence of electric field in the experimental process, which makes it difficult to calculate the combustion efficiency of hydrogen-oxygen combustion under the current microwave ignition. Of course, in the follow-up process, we will carry out electric ignition comparison experiments to reverse the combustion efficiency under microwave ignition by comparing the difference in thrust.
About comment 14, the previous conclusion is not very relevant to the whole, and now we have rewritten the whole conclusion, combining the experimental data above, and pointing out the direction of the research to be carried out in the follow-up.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe experimental study presented in this manuscript investigates the pulse operating characteristics of a water electrolytic chemical propulsion engine using microwave ignition technology. Based on the comments below, the reviewer suggests it requires a significant revision.
(1) The reference number "[1]" is missed in this manuscript.
(2) Introduction: In the last two paragraphs, the presentation of the novelty of this study should be enhanced compared to previous literature.
(3) The discussion of each figure should be presented before the corresponding figure.
(4) Figure 6, Figure 8, Figure 10, Figure 12: The words in these figures are tough to read due to their size and resolution. The reviewer recommends that the words and figures be enlarged to be more readable.
(5) Regarding the description of Figure 16, It would be better to include some specific results obtained at a quantitative level.
(6) This manuscript has some "Error! Reference source not found" that should be corrected.
(7) What about the repeatability of the experimental results? What about the error bars in experimental results? What measures have been applied to minimize the errors?
(8) More description should be included in the experimental systems, especially the details and specifications.
Author Response
Your contribution in suggesting an improvement to the content of the paper is greatly appreciated. Please find below my response to your suggestion.
About comment 1, 3, we acknowledge that the thesis layout was not optimized. We appreciate the feedback and have made the necessary corrections.
About comment 2, the conclusion of the introduction has been modified to more clearly articulate the merits of microwave direct ignition.
About comment 4, I have redrawn Figures 6, 8, and 10, resizing the linearity and text, and I have rearranged Figure 12, enlarging the image.
About comment 5, the initial depiction was found to be lacking in complexity and lacking in certain details. The depiction has since been revised.
About comment 6, it was determined that the initial inspection process was not sufficiently rigorous. Only the initial photographs were subjected to cross-references, and cross-references have since been incorporated for all photographs.
About comment 7, it should be noted that the data presented in this thesis is derived from a single experiment that did not yield error bands. This experiment will be followed up with a repetitive experiment to ensure the robustness of the findings. The existing error is attributable to the precision of the measuring equipment, with an error margin of 0.5%.
About comment 8, the parameters of the individual instruments of the observing system have been incorporated.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThis study offers a new approach to ignite and understand the transient flame characteristics.
There are too many references to institutions regarding the method of micro-ignition. More references should be based on a literature review of reputed journal papers.
Line 169, replace gases with water vapour, the only combustion product.
Line 171, find an alternative to 'wait'.
Lines 171 - 177, write in paragraph style.
Line 186, it should be QWCRC.
Line 200, please give the ignition pulse duration to calculate the ignition energy.
Line 225: 300W appears again.
Figs. 4, 7, 9, and 11—Unfortunately, despite communicating with the authors, the details on the flame images could be enhanced. The authors and the journal publisher are responsible for their quality.
Line 382, there is no mention of 543% in the main text. How is this is obtained, relative to which study/method?
Lines 348 - 349: How does the pressure pulse of 2s and the thrust of 2.25 N help calculate the power?
For example, 348-352 (the words peak and maximum are repeated five times, and thrust appears five times).
The figure captions are short, which is unusual in a research paper. There should be enough detail to help the reader understand the details independently without needing to read the text.
Fig.8c) it is not evident why the pressure of O2 is high and that of H2 is atm.
The literature review for lines 131 to 150 is not exhaustive. The reasons given in two citations do not justify how the pulse operating method benefits.
All images/plots/charts have to be improved in quality.
The language needs editing throughout the paper:
The caption for Fig.15 is not detailed enough.
Overall, in terms of writing and presentation, it is equivalent to the standard of a student project report.
If this is not improved—which is not hard, in addition to the figures 4, 7, and 9—the essential results of the experiment are clear, and therefore, I reject this paper.
Comments on the Quality of English LanguageIt needs proofreading. I added a few comments and should be taken those for the whole manuscript.
Author Response
- Line 169, replace gases with water vapour, the only combustion product.
- Line 171, find an alternative to 'wait'.
- Lines 171 - 177, write in paragraph style.
- Line 186, it should be QWCRC.
- Line 200, please give the ignition pulse duration to calculate the ignition energy.
- Line 225: 300W appears again.
- 4, 7, 9, and 11—Unfortunately, despite communicating with the authors, the details on the flame images could be enhanced. The authors and the journal publisher are responsible for their quality.
- Line 382, there is no mention of 543% in the main text. How is this is obtained, relative to which study/method?
- Lines 348 - 349: How does the pressure pulse of 2s and the thrust of 2.25 N help calculate the power?
- For example, 348-352 (the words peak and maximum are repeated five times, and thrust appears five times).
- The figure captions are short, which is unusual in a research paper. There should be enough detail to help the reader understand the details independently without needing to read the text.
- 8c) it is not evident why the pressure of O2 is high and that of H2 is atm.
- The literature review for lines 131 to 150 is not exhaustive. The reasons given in two citations do not justify how the pulse operating method benefits.
- All images/plots/charts have to be improved in quality.
- The language needs editing throughout the paper:
- The caption for Fig.15 is not detailed enough.
Thank you very much for your suggestion, we have corrected the content of the paper, above is the numbering of the errors that I made to you, and below is my response to your suggestion.
About comment 1 and 2, they are problems with the layout of our paper, and About comment3, 4, 6, and 10, they are problems with the translation of our paper, which have now been corrected.About comment 15, we have rewritten the problematic parts of the paper.
About comment 5, the ignition pulse duration was put on line 270.
About comment 7, since the flame image was indeed too dark, we corrected it by changing the presentation to a different form, drawing an overlay of the flame image and a contour map of the flame image so that it can be clearly displayed.
About comment 8, we have rewritten the whole conclusion, and combined the experimental data above, the 543% you mentioned was our mistake, and now it has been corrected to 508%. This data is derived from the maximum thrust of case3 and case2.
About comment 9, the thruster in the experimental system of this paper is to ionize the oxygen into plasma torch through direct microwave feed, which enters the combustion chamber to ignite the hydrogen gas and ejects it through the nozzle to generate thrust. The power of microwave feed is fixed during the experiment, which is 300 W. Therefore, we consider 300 W as the input data rather than calculated from the thrust results.
About comment 11, we have re-edited the figure notes of Figs. 14, 15, and 16 to include more details.
About comment 12, we redrew Figs. 6, 8, and 10 to improve its visibility. Because this experiment is ultra-thin combustion, the pressure of oxygen is much greater than that of hydrogen.
About comment 13, we have redrawn the end of the introduction.
About comment 14, 15, we redrew Figs. 6, 8, and 10, bolding the lines and text, changed the presentation of Figs. 7, 9, and 11, using flame overlays and contour plots, reformatted Fig. 12, and supplemented some details about the figure notes on Figs. 14, 15, and 16 .
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe manuscript has been significantly revised. However, there are still composition errors in the revision, which should be carefully checked.
Author Response
Thank you very much for your suggestions, we have revised the content of the paper with the following changes.
- we reduced the contrast and brightness of Fig. 4 so that the flames on it can be presented more clearly, and added the moment of capture of the figure in the lower left corner of each figure, so that the textual description of the following is easier to understand.
- We have added pseudo-coloring maps in Fig. 7, Fig. 9, and Fig. 11 with corresponding text descriptions, which is the visibility of the flame shapes increased.
- Concerning Figs. 7, 9, and 11, we replaced the labels with a scale and indicated the time interval at which each flame image was generated in the text caption.
- we extracted the length and area of the flames and pointed out in line229 what needs to be noted for calculating the quantitative data, added the length and area data of the flames at 3.2, and added a side-by-side comparison of the data at 3.4
- We checked the full text for places where cross-references were needed, found two omissions of cross-references, and added them.
- We checked the position of all the pictures, found two places where the pictures are located above the text description, and revised them.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors have made some good revisions, but not all. The manuscripts still should be improved with the following comments.
(1) The reference number "[1]" is missing in the main text of this manuscript.
(2) This manuscript has some "Error! Reference source not found" that should be corrected, such as: line 172, line 191, line 285, etc.
(3) The discussion of each figure should be presented before its corresponding figure, for example, regarding Figure 1 and Figure 3.
Author Response
Thank you very much for your suggestions, we have revised the content of the paper and here is my response to your suggestions.
Regarding evaluation 1, the reference number [1] is located in the fifth word of line29.
Regarding evaluation 2, this is because the original cross-references were overwritten when the original text was revised. I will check the cross-references in the whole paper after I have finished revising the paper from this lesson.
Regarding evaluation 3, it was a problem with our layout, which has now been revised.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsDear Authors
It is a good improvement. I would like you to consider and address these in the next revised version:
The changes are still not sufficient. Here are my suggestions:
1) the authors provide higher contrast versions, with adjusted > brightness/contrast levels
2) provide supplementary processed versions with pseudo-colouring to enhance visibility
3) to add scale bars and clear labelling of what each frame represents
4) number each image, > and provide explanation of each image in order, showing continuous changes to help readers understand what they should be seeing
5) provide quantitative data extracted from the images (in the form of graphs/charts).
6) add a clear explanatory text acknowledging the limitations of the imaging.
Author Response
Thank you very much for your suggestions, we have revised the content of the paper and here is my response to your suggestions.
Regarding Evaluation 1 and Evaluation 4, we reduced the contrast and brightness of Figure 4 so that the flames on it can be presented more clearly, and added the moment of capture of that figure in the lower left corner of each figure to make the textual description of the following easier to understand.
Regarding evaluation 2, we have added pseudo-coloring maps in Fig. 7, Fig. 9, and Fig. 11 with corresponding text descriptions.
Regarding evaluation 3, we not only replaced the labels with scales, but also pointed out the time intervals at which each flame picture was generated in the textual description.
Regarding Evaluation 5, we extracted the length and area of the flames and pointed out in line229 what needs to be noted for calculating the quantitative data, added the length and area data of the flames at 3.2, and added a side-by-side comparison of the data at 3.4
Author Response File: Author Response.docx
Round 3
Reviewer 2 Report
Comments and Suggestions for AuthorsGood revisions. Accepted.
Reviewer 3 Report
Comments and Suggestions for AuthorsAccepted.
