Influence of Porous Media Aperture Arrangement on CH₄/Air Combustion Characteristics in Micro Combustor

Round 1

Reviewer 1 Report

In the present work, Wang et al. propose a strategy of embedding porous media inside micro-combustors to enhance heat transfer and retain combustion stability. The authors carried out a comprehensive numerical investigation of the effects of PM layout, d/D in porous media, and porosity gradient on combustion behaviors. This manuscript was well organized with an in-depth analysis. The knowledge gained from this work offers guidance for future numerical research and highlights the promise of the practical application of the porous media for micro-combustors. I recommend acceptance in Processes after addressing the following concerns:

1. The reaction mechanism used for simulation should be specified.
2. How did the authors deal with the heat loss towards the environment? 
3. How was the layout of porous media optimized?
4. The definition of methane conversion efficiency was missing and should be described.
5. The authors highlighted the role of the small- and large-pore porous media embedded in the inner and outer layers, respectively, in improving the methane conversion. Nevertheless, in my opinion, the conversion efficiency (97.4%) over A:10-30 is quite similar to the other two candidates (95.3% of A:30-10 and 96.6% of A:30-30). More arguments or discussions should be provided to corroborate this conclusion.
6. Iteration parameters such as the step size should be provided; the parameters should be described following the equations.
7. Typo, format, and grammar issues should be addressed, such as

1. “Δn=10 PPI and Δn=10 PPI” in the row of 496.
2. Subscripts, e.g., CH4, Al2O3
3. Abbreviations should be defined at their first mention, e.g, “A:10-30” and “MC-U20”
4. Tense consistency and the use of prep. and art.

Author Response

Thank you for your careful reading and suggestions. The relevant changes are shown in a separate file.

Author Response File: Author Response.docx

Reviewer 2 Report

This is an interesting work addressing an important topic. It has the potential to be published in Processes. However, I have the following comments that the authors should implement in the revised manuscript before publication.

1) Introduction - It should be better stressed, citing relevant literature that, at the micro-scale, even a partial catalyst-coating of the reactor walls is beneficial to combustion (see, e.g., Chemical Engineering Science, 2014, Volume 116, Pages 350-358; Catalysis Today, 2009, Volume 147, Pages S156-S161). In addition, recent literature findings related to U-shaped heat-recirculation micro-combustors should be briefly discussed (see, e.g., Applied Sciences, 2021, Volume 11, Issue 12, Article number 5418; Chemical Engineering Research and Design, 2021, Volume 173, Pages 15-26).

2) Introduction - The connection between aim of the work and literature gaps should be better described, thus giving more strength to the reason behind this work.

3) Numerical simulation verification - Are there further data to extend the model validation?

4) In the discussion, the practical impact of the results obtained in this work should be better highlighted. This should also be done better in the section “Conclusions”.

5) Conclusions - The authors should also give an outlook on future research work.

I’m willing to review the revised manuscript.

Author Response

Thank you for your careful reading and suggestions. The relevant changes are shown in a separate file.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Overall, the manuscript has been improved after revisions. I have only the following comments that should be implemented in the revised manuscript before publication.

1) With reference to my first comment of the first round of review, the doi of the manuscript that you were not able to retrieve is https://doi.org/10.3390/app11125418

2) Please, double-check references in the revised manuscript: names have been confused with surnames for 3 manuscripts.

3) The right year for reference [18] is 2009 (and not 2017).

Author Response

Thanks to the editors and reviewers for their careful review and valuable suggestions, we have made corrections one by one in a separate document.

Author Response File: Author Response.docx