Effects of Ozone Addition on Multi-Wave Modes of Hydrogen–Air Rotating Detonations
Round 1
Reviewer 1 Report
- Summary
This paper is on a 2D numerical study of rotating detonation engine (RDE) that runs on H2-air and the effects total temperature and ozone addition have on the RDE behavior. The authors show interesting results regarding detonation wave mode and performance implications in the RDE with respect to the aforementioned total temperature and ozone concentration tests. This reviewer recommends this manuscript for publishing, after the below comments are properly addressed.
- Abstract
lines 38-39
RDEs do not have to be premixed, the statement in these lines regarding how RDEs contrast to ODEs/PDEs is incomplete
- Introduction
The literature review is lacking, and should be expanded. Please see comments regarding citations / references in the Conclusion and References feedback in this letter.
- Methodology
It's mentioned briefly, but it should be expanded that this is a premixed simulation, in that, the propellants are fed in premixed via the injectors.
Discussion should be added on when the solution is considered to have a reached a steady state / limit cycle, especially since premixed simulations in RDEs can take a large amount of physical time to reach steady state.
Was each test case where total temperature and ozone concentrations varied from the initial conditions or was a steady state reached then the total temperature or ozone concentration varied, then the solution allowed to reach a new steady state? Either way, this needs to be added to the paper
- Results
section 3.1
It is unclear as to where and how the total temperature is altered in the flow-field. Please expand on this in either the methodology and/or the results sections.
Figures 3a,3b,3c, and 3d do not appear to have reached a steady-state solution
section 3.2
It is unclear as to where and how ozone is altered in the flow-field. Please expand on this in either the methodology and/or the results sections.
line 159
A citation, expansion, or removal of the statement regarding Rayleigh-Taylor instability at the contact surface between the fresh propellants and the burned products needs to be addressed
Figure 5a
What is the cause of the propellant fill-zone shape change? As this appears to be either an unstable more or a non-converged solution (i.e., reached steady state). Please expand discussion in paper accordingly.
Figures 7, 8, and 9 appear to be the biggest results of the paper, consider expanding upon them in the results/conclusions.
Table 1 mentions heat release, but not for where. Is this overall heat release in the entire computationaly domain or chamber?
Also, there should be a distinction on whether the heat release zones mentioned are for detonation or deflagration.
- Conclusion
Conclusion (4) is effectively a re-statement regarding parasitic deflagration and the effect it has on RDEs. There are several authors who have published on this work, i.e., Gamba, Chacon, Cocks et al., Strakey et al., and others, but are not referenced regarding their agreement with the authors' findings, or mentioned in this manuscript at all, and should be cited.
- References
There are many more references on RDEs/RDREs/RDCs that must be included.
For instance,
1. there is a paper by Daniel E. Paxson published earlier this year that discusses the relationship between number of waves and performance and it is not included in the references list.
2. Another paper by Kumar et al. discusses ozone and RDEs; it is also not included in the references.
The quality of English in this paper is quite good.
Author Response
Please refer to the attachment
Author Response File: 
Author Response.docx
Reviewer 2 Report
The authors studied the effects of ozone addition on hydrogen air rotating detonations. The topic is interesting and fits the scope of this journal. Here are my comments and questions:
1. How the authors define the detonation in the simulation?
2. Have the authors considered about the heat loss and wall effects?
3. The authors mentioned the structure may also be impacted by R-T instability in line 159. What is the time scale of this flow motion? R-T instability usually happens at relatively longer time scale.
4. O3, H2, O2...should have subscript.
5. A Nomenclature can be useful in this paper.
6. Ozone only not can be used to promote low-temperature oxidation but intermediate temperature oxidation as well, for example, warm flame formation (https://doi.org/10.1016/j.proci.2022.06.007). The authors may want to discuss it in the introduction.
Author Response
Please refer to the attachment
Author Response File: Author Response.docx
Reviewer 3 Report
The manuscript presents a numerical study on the effect of ozone concentration within hydrogen-air mixtures on rotating detonation waves (RDWs). The rotating detonation combustor is simplified as a flat 2D rectangular shape with periodic boundary conditions. The results clearly show that ozone addition increases the number of RDWs and stabilizes detonation propagation at low inlet temperature conditions, while the addition has a negligible effect on combustion performance. The topic is very interesting for researchers in similar fields, and the conclusions are logically derived. However, some descriptions are unclear, and some of the authors' claims seem not to be clearly mentioned. See following comments.
1. Abbreviations are defined multiple times. Delete duplicated definitions. For example,
A. PDEs in Line 33 is redefined in line 34.
B. RDE in Line 34 is redefined in lines 38, 46, 53, 54, 76, and so on.
2. Line 33: Insert space. “… (ODEs) [1]and rotating …” => “… (ODEs) [1] and rotating …”
3. Line 63: “… O3 to an H2/O2 mixture …” => “… O3 to an H2/O2 mixture …”
4. Lines 72 and 91: “… O3 …” => “… O3 …”
5. Line 92: Add the full name of “KNP”. Add references for the KNP scheme.
6. Line 104: “The maximum to minimum ratio”. the maximum and minimum of which parameter? Of the cell?
7. Line 105: Authors used a cell size of 100 μm. Is it small enough to capture the detonation cells? The cell size with hydrogen is quite small.
8. Eqs. (6-7): Add definitions of T, Tst, R, and γ. Which pressure and temperature are pst and Tst? At the inlet boundaries?
9. Figure 2: The temperature fields with both cell sizes look similar, but the pressure peaks (Chapman-Jouguet pressure) for both have a huge difference. This difference may affect outlet performance. How can authors guarantee that the cell size of 100 μm is optimized?
10. Figure 2: Authors should also check other properties, e.g., temperature, to assess the feasibility of the 100-μm cell size.
11. Section 3.1: Effect of inlet total temperature? The title of this section is unclear.
12. Line 138: "H2" => "H2"
13. Line 142: Where is the recirculation zone for case (a) in Figure 3?
14. The abbreviation "RDW" is used without definition. The definition appears in Line 200.
15. Figures 4 and 5: I recommend inserting a 0% addition case to enable a clear comparison of the results.
16. Line 232: What is the basis for the authors' claim, "the production of OH, a crucial indicator of the detonation reaction"? Add references for it.
17. Line 249: If the authors use a 50 μm cell size, this conclusion may change.
18. Lines 258-259: Increase in inlet total temperature? Decrease in inlet total pressure? Make these expressions clearer throughout the manuscript.
19. Line 261: "... significant affect the total pressure ..." => "... significant effect on the total pressure ..."?
20. Line 289: Duplicated definition of "RDWs".
21. Line 301: The meaning of this sentence is unclear. "However, ozone has no noticeable impact on detonation wave propagation ...". What does "detonation wave propagation" mean?
22. Line 303: This sentence is also unclear. It does not seem to convey what the authors intended to address, for example, "A small amount of ozone addition can improve RDW inception when the equivalence ratio is greater than 1."
Overall, typo-check is required.
Author Response
Please refer to the attachment
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
Accept
Reviewer 3 Report
The authors have addressed the points in question and corrected the typos. The revised manuscript is now suitable for publication.
