Similarity Analysis for Time Series-Based 2D Temperature Measurement of Engine Exhaust Gas in TDLAT

Round 1

Reviewer 1 Report

See attached review.

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

Thank you very much for taking your precious time to review our paper. It was a great opportunity to discover new areas of research through your review. We first changed the title to a suitable subject for the scope of the study and also made efforts to reflect your valuable opinions, but some of the comments were thought to require more in-depth research, so we planned for future research. The following is an answer to your opinion. Finally, the limitations of this study and future research plans have been put together in the conclusions.

Author Response File: Author Response.pdf

Reviewer 2 Report

In the present work the authors report  a technique to measure two-dimensional (2D) temperature and analyze the species concentration and emission of pollutants in output of a from combustion systems. The method is based on the measure of the optical absorption through Tunable diode laser absorption tomography (TDLAT).

This is an interesting paper and the authors show that the method can analyze emission of pollutants  with fast-response and non-contact.

I have some minor revisions request:

In the description of the setup (100-101) they said that the laser was split in 16 channel, then that “10 splitted beams are irradiated into 10 collimators”. Is there any error? The authors should better explain the paths of the laser shown in Fig.3. They say “Multiple parallel laser beams pass through the region of interest..…… The laser path consists of 10 real beams in a 5×5 layout and 8 interpolated virtual beams. The cell length through which the laser passes in the measurement area is 60 mm and the spatial region for CT analysis consist of 144 (12×12) square grids with a grid size of 117 2.5×2.5 mm.” What exactly means interpolated virtual beams? How was this interpolation made? In the figure 4 the authors report the 2D temperature distribution retrieved from the experimental measured absorbance spectra. The 2D distribution refers to an area of 40x40mm is well spatially-resolved with at least 1pixes/mm, but it is obtained from spectra measured at only 10 laser paths (5 on x-direction and 5 on y-direction). Was any postprocessing of the data employed like spatial interpolation? As far as the analysis of species is concerned, can the author comment on the comparison of exploit linear absorption with respect to other laser techniques such as (for example) Raman spectroscopy.

Author Response

Dear Reviewer,

Thank you very much for taking your precious time to review our paper. It was a great opportunity to discover new areas of research through your review. We first changed the title to a suitable subject for the scope of the study and also made efforts to reflect your valuable opinions. The following is an answer to your opinion. Finally, the limitations of this study and future research plans have been put together in the conclusions.

Author Response File: Author Response.pdf

Reviewer 3 Report

p. 3 r. 101: The laser is splitted in 16 channels then only 10 are used. To be explained.
p. 3 r. 116: What is a virtual beam?
p. 4 r. 134: Why distorting raw signals?

In my opinion, the paper could benefit by some more consideration on the physics of the experiment itself. For example, which is the engine idle speed? As most four stroke engines of that size idle between 600-1800 rpm, temperature fluctuations should be detectable as they will be expected at 5 to 15 Hz.
I would add some more considerations showing for example the temperature measurement in different points as a function of time, while especially trying to average only a few cycles together (per measurement) to provide high time resolution.
Also, I think that the most important advantage of this measurement method is not low noise or accuracy against a reference thermometer but spatial- and time-domain resolution, and this could be stressed way more in the paper.

Author Response

Dear Reviewer,

Thank you very much for taking your precious time to review our paper. It was a great opportunity to discover new areas of research through your review. We first changed the title to a suitable subject for the scope of the study and also made efforts to reflect your valuable opinions. The following is an answer to your opinion. Finally, the limitations of this study and future research plans have been put together in the conclusions.

Author Response File: Author Response.pdf

Reviewer 4 Report

I have a very good impression on the current manuscript dealing with TDLAT of engine exhaust gas

The authors provided an excellent review of the existing papers so that I can recommend the paper for publication with some minor corrections/suggestion.

Could you please define TDLAS in the paper as well. Do you mean tunable diode laser absorption spectroscopy or tunable diode laser absorption system? If spectroscopy I think it would be appropriate to provide the reference to the latest papers of MDPI dealing with this diagnostics even if the paper from other journals. I’ve found for instance.

 

Dickheuer et al, Atoms 2019, 7, 48; doi:10.3390/atoms7020048   

 

TDLAS is very general diagnostics used in many topics of physics !!

 

I would also recommend to replace the Reference 9 with general “mathematical” paper or description of Voigt profile. Could one explains which value defines the Lorentzian part in your case ? And provide the numbers used. There is a point I slightly misunderstood. Authors reconstruct the temperature by comparison the theoretical spectrum with the measured data. Can they provide the example of such comparison in a simple 2D Plot for one laser. Line 74, page, you mean probably cm-1 not cm1?

Author Response

Dear Reviewer,

Thank you very much for taking your precious time to review our paper. It was a great opportunity to discover new areas of research through your review. We first changed the title to a suitable subject for the scope of the study and also made efforts to reflect your valuable opinions. The following is an answer to your opinion. Finally, the limitations of this study and future research plans have been put together in the conclusions.

Author Response File: Author Response.pdf