Experimental Pressure Gain Analysis of Pulsed Detonation Engine

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper study a pulse detonation chamber (PDC) equipped with Hartmann–Sprenger resonators. Hydrogen / air and Hydrogen/Oxygen mixture were tested. A full – factorial experimental campaign employing four factors with four levels each has been carried out for both the mixtures. This paper is of guiding significance for the design of short-distance PDC. However, the following issues should be addressed.

1. In this paper, the pressure characteristics of the PDC are studied through experiments, but the introduction of the test system is not comprehensive. For example, the key size data of the PDC, the parameters of the sensor in the test system, the sampling frequency of the acquisition system and other necessary information are missing.

2. In this paper, the peak value of the pressure data is very low, what are the initial conditions of the reactants in the PDC, what is the corresponding theoretical C-J pressure, and how to prove that detonation waves are formed in the PDC with such a low peak pressure? It is advisable to measure the propagation velocity of the combustion wave to prove whether a detonation wave is formed.

3. In the introduction of this paper, a lot of space is devoted to the description of RDE and ODE, which is not too relevant to the research object of this paper, and it is recommended to add references related to the research content of this paper.

Author Response

Thank you for taking the time to review our paper. Please find attached our rebuttal.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The paper describes an experimental campaign of a pulse detonation combustor (PDC). The PDC utilizes Hartmann – Sprenger resonators to shorten the length of the combustor. The paper is overall well-written, but paper requires edits and addressing of questions prior to publication.

 

Line 51 the rarefaction wave is generated from a combination of the forward leaning detonation and triple point interface with the slip line. See: The ground impulse generated by a plane fuel-air explosion with side relief, Sichel and Foster, 1979

 

Line 53-54 “while the operating frequency is dependent on the CJ detonation speed”

 

CJ speed affects RDE operational frequency, however, operational frequency is more of a product of the mixture and mass flow rate, as detonations in RDEs rarely propagate at CJ. This statement should be worded.

 

Figures 4-7 show a pressure rises on the order of 2-3 bar along with pressure signals that do not have the expected signal of a detonation. Please comment on the low measured pressures as for instance, a hydrogen-oxygen detonation at stoichiometric conditions, has a peak pressure of about 18 bar.

 

What are the observed wave speeds in the PDC?

 

Line 430 “also supported by Schlieren visualizations and chemiluminescence measurements not included here”

 

Why not include at least a sample of the schlieren images and chemiluminescence in the results of this paper? This may help to show the operation of the PDC and address questions regarding the low observed pressure signals. 

Is coupling captured in the chemiluminescence and shock fronts images from the schlieren, as described in lines148 and 149 of the text?

Author Response

Thank you very much for taking the time to review our paper. Please find attached our answers. 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The comments made by the reviewers have been revised and the article can be accepted.

Author Response

Thank you for taking the time to review our paper. We appreciate the valuable comments and your input.

Reviewer 2 Report

Comments and Suggestions for Authors

Thank you for making the necessary edits to this manuscript. This reviewer suggest the manuscript for publication upon addressing the 2 minor edits.

1. In the previous comment to the authors, the wave speeds in the PDC were requested. This question was missed in the reply. Please address.

2. The authors removed the statement from the conclusions section stating that visualizations were not included in this paper, and updated it to read as follows with a citation on lines 480-481: "Based on the shape of the recorded pressure signals, also supported by Schlieren visualizations [34]".

This reviewer suggests moving the citation and including text to describe their supported visualization results from the conclusions and moving the citation into an appropriate area in the results and discussion section, as the conclusions should be about the conclusions of this paper and not another paper. Of course, it is encouraged to state the agreement in the results section of this paper that corraborates results from other work.

Comments on the Quality of English Language

Typo on line 481 reads: reachedsustained

Should be: reached sustained

Author Response

Thank you for taking the time to review our paper. We appreciate the valuable comments and your input.

C1. In the previous comment to the authors, the wave speeds in the PDC were requested. This question was missed in the reply. Please address.

R1. We are sorry for missing the reply to this question. The wave speeds have been added for the Schlieren examples that are now included in the Results and Discussion, subsection 2.3.5. We cannot further disclose other wave speeds due to a conflict of interests with other publication under review.

 

2. The authors removed the statement from the conclusions section stating that visualizations were not included in this paper, and updated it to read as follows with a citation on lines 480-481: "Based on the shape of the recorded pressure signals, also supported by Schlieren visualizations [34]". This reviewer suggests moving the citation and including text to describe their supported visualization results from the conclusions and moving the citation into an appropriate area in the results and discussion section, as the conclusions should be about the conclusions of this paper and not another paper. Of course, it is encouraged to state the agreement in the results section of this paper that corraborates results from other work.

R2. As mentioned before, Schlieren examples for both oxidizers have been added in subsection 3.2.5 and addressed in detail,  including velocity estimations for key features of the PDC cycle. In addition, the description of the Schlieren set-up system  has been added in subsection 2.3.

 

Once again thank you for your valuable suggestions to improve our manuscript. We hope that the revision has addressed all the issues in the old version.

We are looking forward to your positive response.

Best regards,

The authors.