Continuous Detonation Combustor Operating on a Methane–Oxygen Mixture: Test Fires, Thrust Performance, and Thermal State

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1. The less important information such as the number information in line 79 does not need to be wasted in the main text.
2. Line 66 uses the expression "combustor". Why is the expression "combustion chamber" used in lines 84 to 101, and the use of the abbreviation "CC" makes the reading efficiency extremely poor? Why not directly use "combustor"?
3. It is mentioned in lines 90-91 that "The fire walls of the CC are made of copper." Where is the location of the firewall in Figure 1 and will it encounter the detonation wave? The melting point of copper is less than 1300 K, and the temperature of the detonation wave is as high as over 1800 K. Why is copper material chosen? Will it cause the combustor to have melting damage?
4. It is questionable why the ignition position of ignition electrode in Figure 1(a) is at the expansion of the conical central body, and the detonation wave obtained by ignition at this position can propagate countercurrent along the convergent channel to form a stable rotating detonation wave in the annular combustor?
5. Why are there no annotations marked on the two left channels of Ignition electrode in Figure 1(a)? Where is the cooling water outlet of the conical central body?
6. Line 142 to 153, could the positions of the sensors be illustrated with pictures?
7. Why did the pressure in the test fire 3 suddenly rise so high? What is the purpose? Considering that the combustion chamber fire wall uses copper, is this pressure too unreasonable?
8. The tops of Figures 4(a) and 5(a) have been cut off. Please replace the pictures.
9. The pressure signal in Figure 8 does not look like the pressure signal of a detonation wave, but more like that of a Sawtooth wave [1].
10. For Figures 8 (a) and (b), please keep the widths aligned and mark the specific values of the feature frequencies.
11. How is the power, average heat flux, and Q_L in Table 3 obtained?
12. Why is test fire 3 in Figure 9 significantly higher than the impulse in reference [7] before burnout? Are there any reasonable explanations? Furthermore, as can be seen from Figure 2 and Figure 10 in the appendix, the flame color at the outlet all presents the green color of the copper flame reaction, indicating that copper is melted and blown out by the high-speed gas flow in each experiment. Has the melting loss been checked after each experiment?

 

[1]   H. Peng, S. Liu, W. Liu, H. Zhang, X. Yuan, J. Yu, S. Huang, The nature of sawtooth wave and its distinction from continuous rotating detonation wave, Proceedings of the Combustion Institute (2022).

 

 

 

Author Response

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Reviewer 2 Report

Comments and Suggestions for Authors

This paper presents a parametric experimental study of a methane–oxygen rotating detonation combustor, focusing on thrust and thermal behavior during long-duration operation, in contrast to most work reported in the open literature. The study is thorough and provides data and details useful to the pressure-gain combustion community. I have no comments or suggestions and recommend the paper for publication as is.

Author Response

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Thank you very much for your attitude to our work and kind words.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors This paper presents a continuous detonation combustor (CDC) operating on a methane–oxygen mixture, which is considered appropriate for the journal and likely to draw the reader's interest. The experiment is well presented, and the results are clearly explained. I think the paper can be published after clarification of some significant issues, and the following comments should be addressed in the revised version. 1. The objective of this work is to continue research into increasing the sea-level specific impulse of the detonative combustor (DC), extending its operational life, and determining the thermal state of its structural components. However, the research motivation and background are not well presented in the introduction. Therefore, I suggest adding references and providing a deep research gap analysis of a continuous detonation combustor operating on a methane-oxygen mixture. The strong point to explore the test fires, thrust performance, and thermal state for this topic should be described scientifically. 2. I suggest presenting a detailed explanation of the physical model, chemical reaction, Chapman–Jouguet (CJ) analysis, and governing equations for a continuous detonation combustor operating on a methane-oxygen mixture. It is beneficial to provide a scientific analysis of experimental results.   3. I think the performance of a methane–oxygen mixture CDC is affected by combustor design. Please provide a more detailed consideration of the design and modifications to the test rig and combustor for the experiment. Therefore, this discussion offers a clear framework for understanding how combustor geometry and test-rig configuration influence detonation stability and performance in methane–oxygen CDC. 4. It is better to present the assumptions and limitations of the fire test result because only specific combustion was used. 5. The test fire results and discussion have already provided detailed numerical data. However, I recommend expanding the discussion by explaining the practical implications of the research result. Therefore, it provides insight into how the CDC experimental findings on the methane–oxygen mixture translate into practical combustor design and operational guidelines.

Author Response

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Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

This paper has been revised properly. 

Reviewer 3 Report

Comments and Suggestions for Authors

The paper can be accepted now.