Combustion Instability of Swirl Premixed Flame with Dielectric Barrier Discharge Plasma

Round 1

Reviewer 1 Report

Abstract needs to be rewritten as it contains details from the paper that is not self explanatory.

equation 1 is not well represented. it is not clear what the authors mean by H f, A=

page 8, line 207, instead of giving a refrence [19], there need to be a discussion and physical reasoning for the observed results

page 8: conclusions made in lines 213 to 217 needs some attention, namely explanation and demonstration.

a proper physical treatment of the figure 7 to 10 is required. with it, it is just a report of tasks done. it is not enough to explain the trend in the figures but to explain and further detail the consequences of the observations.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

The authors investigated the effect of plasma on combustion instability of methane premixed flame under acoustic excitation.  Major revision is definitely needed before publication. 

1. Authors need to go through whole paper to check the language. Some examples: Line 11, what is ', and' ?; line 87, 'to measure flame OH radical concentration measurement'?; line 89 'flame Mechanism', why use uppercase letter?; line 95-97, miss subject; line 113, 'Complex frequency domain signal', confusing as a sentence;  .......
2. Planar laser-induced fluorescence (PLIF). Errors in line 10, 'plane', line 86, 'planner'.
3. The Introduction part needs to be improved. Such as the tense, line 76-78, why 'will be' the future tense was used?  line 82-line 89, the sentence needs to be reformed. 
4. Figures need to be improved. Figure 1, the structure of the burner is not clear, where is the combustion nozzle, also the gas supply (CH4, air) and the PLIF measurement was not cleared presented. Figure 8 and Figure 10, the quality is so bad. Please provide the real position, not just pixels.
5. The captions of the figures, please provide more description. Such as Figure 2.
6. Check Equation (1). 
7. Line 164-line 173, the description of the optical system is confusing (very low quality) and there is some wrong description. The flame heat release rate was measured by a photomultiplier tube with band pass filter, better to provide FWHM. 'The flame front image is obtained by the OH-PLIF system ', actually, according to the Results part, it was based on CH* signal. What is 'the fluorescence signal excited by flame OH radicals' ? OH-PLIF is a technique to measure OH radical under the ground state. Usually, OH* indicates OH radical at excited state. In this work, OH was measured, not OH*. 
8. Section 4.2, please provide some discussion about the results, why the effect of the plasma with different discharge frequency varied? 
9. Why we need figure 9? It provides the same information as figure 8.   plot the distribution of the OH PLIF signal at certain height of the flame with and without plasma in a same figure could make the comparison clearer. Also for the results in Figure 10, the images are not sufficient to support the discussion by the authors, as the difference was to small. Additional figure were needed to plot the signal together for better comparison.
10. Line 250-251 'spatial distribution of the OH radical concentration', actually the images only present the distribution of OH PLIF signal. Not concentration.
11. In this work, the images of OH and CH* are average or single shot?
12. Why didn't use OH-PLIF single shot image to obtain the flame front?
13. Why does the OH distribution have a significant different from the CH* images? 

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors have met my concerns 

Reviewer 2 Report

Authors have addressed most of my comments. 

However, the quality of Figure 8, 9 and 10 needs to be improved significantly， it is so bad. In Figure 8 and Figure 9, even 'CR return' can be seen in the figure, as authors simply took a screenshot. In Figure 8, the font size of the words of the color bars is too small. Figure 9, what is the X, Y axis labels?