Experimental Investigation on the Impact of Varying Air-Inlet Widths and Fuel Pan Diameters on Fire Whirls’ Combustion Characteristics

Round 1

Reviewer 1 Report

The paper titled “Experimental Investigation on Impact of Varying Air-Inlet Widths and Fuel Pan Diameters on Fire Whirls’ Combustion Characteristics” has written nicely. This study may be beneficial for the firefighter's control of wildland fires. Furthermore, it can be more impactful after incorporating the following comments:

1)      Referring Fig.1 is quite difficult, please enhance the font quality and size.

2)      Calculate the amount of air entering around fire whirl with varying air-inlet width and pan diameters.

3)      Results (Flame height & Axial Temperatures) may be compared with other research papers having fire whirl studies.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The authors have studied experimentally a fire whirl using a small-scale pool fire formed with n-heptane. The pan diameter was varied in the range from 5 cm to 18 cm, and the swirling airflow was formed by using four slits placed around the pool fire. By varying the width of the slits, combustion characteristics such as flame height of the fire whirl, heat release rate and so on, are discussed in the manuscript.

Experimental data were obtained reliably, and the data are valuable for fire research. However, there are some points of concern. It would be desirable to correct them before the paper is published in the journal.

1.     What is the definition of "the flame temperature" on page 4, line 111? Basically, flame temperature, in combustion science, refers to the local temperature measured in the reaction zone of a diffusion flame.

2.     On page 4, line 111, the authors described that k-type thermocouples were used and the temperature data were corrected for heat loss due to radiative heat transfer from the mearing point of the thermocouple. In the thermal correction for the thermocouple measurement, do the authors take into account the error of heat conduction through the thermocouple wires?

 3.     What kind of combustion phenomenon does "fuel combustion" in line 138 on page 4 refer to?

 4.     In page 4, line 142, the authors state as follows.

 ＞Under consistent fuel pan diameter conditions, the flame height exhibits a negative 140 correlation with the air-inlet width.

 Could this be due to a decrease in the magnitude of the axial velocity of the swirling flow as the slit width increases?

Basically, the flame is not cooled by the air. Therefore, the following statement in line 143 is not appropriate. 

5.     What does "burning rates" on page 5, line 175 mean in terms of combustion science?　The author should clarify the definition of "burning rates" used here.

 6.     A fire whirl is a diffusion flame with a swirling flow. In this sense, it makes sense to discuss how the swirling flow affects the diffusion layer of the flame. However, that kind of discussion is not given in the paper.　The authors should discuss the details of the flame structure as well as the heat generation from the overall combustion zone.

In addition, there are several cases where the English language is not appropriate in describing and explaining the phenomena in this manuscript. Therefore, the text has to be checked by a native English speaker.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Thank you for an interesting report. You explain different aspects of fire whirls, but in a good and educational manner. It's easy to follow along in your lines of thought.

1: In the introduction, I see at least two references studying the effect of air-inlet width, such as [13,14,23], so it is not reasonable to say that “less attention given to the effect of air-inlet width on the combustion characteristics”. Maybe, you should rewrite the introduction by point out the novelty of this study

2: In section 3.1, as for the effect of ambient airflow on the fire whirl. It seems that it has two contradicting effects, one is to support combustion and another is to inhibit combustion. What is the threshold between these two contradicting effects? That is, can the effect of ambient airflow be definite? Please explain more on this. Maybe the following reference on swirling flame can be helpful.

[1] Thermal and emissions characteristics of a turbulent swirling inverse diffusion flame. H.S. Zhen, C.W. Leung*, C.S. Cheung. International Journal of Heat and Mass Transfer, 53 (2010) 902-909.

[2] Dong, L. L. ,  Cheung, C. S. , &  Leung, C. W. . (2021). Heat transfer characteristics of an impinging swirling inverse diffusion butane/air flame jet. Experimental Thermal and Fluid Science, 128, 110438-.

3: For the finding that the burning rate in the quasi-steady-state firstly increases and then decreases with air-inlet width. Please answer me, whether the preparation of the air inlets of different widths, for example, 1, 3, 5 and 7 mm will have a finding totally different from the current finding? It the answer is yes, how about the air-inlets widths if prepared at the values over 7, say, 7, 9, 11, 13mm?

4: For the finding “The fire whirl’s continuous 297 flames can comprise up to 55% of the total flames, a notable “stretch” compared to a 298 buoyant pool fire of identical size”, obviously, the reasoning is not strong and more explanations should be given.

The English needs to be futher impromoved

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

In brief words, the reviewed article represents rare example in my reviewer's practice when I am ready to say: "It can be published as it is".

The article under consideration is devoted to investigations of fire whirls which are very interesting objects from theoretical and practical point of view. Its language is very smooth and easy to read, no typos, wrong order of words, etc. were detected.

Comprehensive list of references contains only important works in the field of interest and effectively supports the author's choice of the main direction of the research as well as experimental and mathematical methods choosen.

From scientific point of view, the reviewed article is not a giant jump in the area of interest but definitely represents a step forward. Well illustrated high quality experimental results and fruitful discussion  including the use of known mathematical approaches, artfully modified by the authors in relation to the goals of their research, eventually allowed them to obtain interesting conclusions that certainly enrich the knowledge about fire whirls.

As a conclusion: I read the article with great pleasure and sincerely congratulate the authors on a job well done.

Author Response

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