Observation of a Signal Suppressing Effect in a Binary Mixture of Glycol-Water Contamination in Engine Oil with Fourier-Transform Infrared Spectroscopy

Round 1

Reviewer 1 Report

Comments:

1. Line 29. Is it the engine oil and lubrication oil is the same oil used for this research? If yes please standardize the terms whether used engine oil or lubrication oil.

2. Line 95. Suggest to demonstrate the different contaminated sample concentrations into one table.

3. Line 121. What do you mean by A similar window was used to cover the first…is it the same KBr window?

4. Line 152. Spacing before O-H

5. Line 153. Please put the equation into one different line.

6. Line 158. Ath wave number of 3400 cm^1, it shows 1% of water as the highest peak compared to others. What is the possible reason?

7. minimize the size of Figure 2 & 3. It’s too big. Please revised accordingly.

8. Line 206-217. Please rearrange the paragraph according to the template. It’s quite difficult to understand.

9. Please put more latest references.

Author Response

Dear Reviewer,

Attached please find the authors' response for your comments.

Thank you

Author Response File: Author Response.pdf

Reviewer 2 Report

This work highlights some of the complexities of the matrix effects of the glycol/water interaction within the oil. Also, it demonstrates the difficulties in quantifying the contaminant concentration when glycol and water both contaminate the engine oil. Thus, it could provide an excellent reference for detecting Glycol Contamination in Engine Oil.

Author Response

Dear Reviewer.

Thank you for your feedback.  They are really appreciated. 

Best

Authors

Reviewer 3 Report

1.       Abstract:

-          Is there wrong word used “until” in this sentence:

Even when taking into account the number of O–H bonds per until volume of contaminant, the matrix effect of the addition of the antifreeze was evident in the signal.

-          Abstract did not show the most important finding.

2.       Improve the Conclusions which reflect the findings from this study.

Author Response

Dear Reviewer,

Attached please find the authors' response for your comments.

Thank you

Author Response File: Author Response.pdf

Reviewer 4 Report

The study presented for the review describes the influence of antifreeze and water contamination on engine oil properties. The introduction clearly presents the authors’ motivation. The presented topic is interesting.  The “preparation” section is written cohesively.

The particular comments on each of the parts are listed below:

1.      “Results and discussion, 3.1. FT-IR Absorption Spectra” – The equation is unclear.

If I understand:

 =

In that way, the equation is much more understandable.

2.      The sentence “such that the number of O–H bonds per unit volume for concentrated ethylene glycol is defined to be 1 with 1% glycol contamination, water is therefore 3.1 with 1% glycol contamination, and 50/50 glycol & water would be 4.1 with 2% 50/50 (glycol/water) contamination” is unclear. I suggest listing all those information in the table.

3.      Figures - The description below figures should just describe the kind of measurement and necessary information. The description like “the peaks around 883 cm-1 (CH2 rocking), 1040 and 1080 cm-1 (C–C and C–O stretching), 1640 cm-1 (O–H bending), and 3400 cm-1 (O–H stretching).” (line 157) should be given in the main text (results).

4.      Figure 1. I suggest marking on the spectra the associated vibration of even the wavenumber. It is easier to analyze the spectra with the description on them.

5.      The main text does not include a description of the lines at about 1450 cm^-1 and about 2900 cm^-1, the most intense peaks on the spectra. Please, add them.

6.      Figure 2. Did the authors measure the absorbance for the samples with 0.0% contamination? If not, there should be deleted measurement points.

7.      In the section “Results and Discussion” and “Conclusion”  the Authors referee the investigated study to the DFT calculation. It should emphasize why those calculations will be interesting. I suggest adding a more detailed discussion.

General comments:

1.         There are lots of double spaces between words. Please, correct it.

2.         I would like to suggest preparing the paper with an agreement with the publisher's template. It is available on the MDPI publisher website.

3.         The sentence “While a reasonable threshold limit exists for small amounts […]” (lines 33-38) is very long. Please try to divide it into shorter ones.

4.         Figure 1. The journal template suggests writing “Figure 1.” Not “Figure 1:”. There is a dot, not a colon. It is common to present the FT-IR spectra starting with the higher wavenumber values.

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

Attached please find the authors' response for your comments.

Thank you

Author Response File: Author Response.pdf