Impact of Ultra-Low Viscosity Fluids on Drivetrain Functionality and Durability

Round 1

Reviewer 1 Report

The manuscript deals with experimental research on ultra-low viscosity fluids on drivetrain.
The experimental goal and test setup are well described. Testing procedure is clearly explained in details. In my opinion, the results presented in the paper are worthy and useful for the automotive industry. Overall structure of the manuscript is perfectly organized. 
I recommend to publish after some small corrections, as follows:

Add a subtitle in line 64 (2.1.1 Base Fluids). The same should be in line 75, 82, 98, 110, 129, 142, etc.
The description given in figure (line 280) are too small to be visible for reading.
The photo captions (pictures, diagrams and graphs) should be corrected to figures.
The references should be numbered 1, 2, 3, etc.

Author Response

Dear reviewer,

Thank you for your very helpful response.

The remarked points are fixed in the latest version of the manuscript.

 

Best Regards

Joerg Franke

 

Reviewer 2 Report

This is an interesting area of research to the readers. The content of the manuscript is original and based on the data from an industrial case. Hence, the content is very practical with high impact. There are a few structural issues and lack of information that needs to be addressed prior to publication.

1. The introduction lacks a review of the previous literature and published research in the area although the problem description is thorough and clear.
2. References should be in a numeric sequence [1],[2], …[n]. The numbering is random throughout the text.
3. Table [T1]: authors can use numeric style in the caption. Table 1, 2, …
4. Table T1: this is a very useful table. However, some information is missing. Readers can differentiate most of the samples in terms of their base fluid API class and additive package. However, there are samples where their information is identical and reader cannot understand the difference; so, cannot justify the difference in the viscosities! For example, Samples E, F and G or samples L, M and N, or samples X, Y and Z insinuate that they are identical samples but without any clear reason to justify why their viscosities are different. It seems a third parameter is required in the table for lubricant classification. Could you please amend the table to indicate what the difference between these samples are?
5. Table 2: The referencing style is not standard for a journal paper. Please use numeric sequences, [1], [2], [3], ..., [n]. These standards should usually be purchased and not easily accessible to academic community. So, some preliminary information regarding the rigs, their set-up and data collection could help the readers to understand the process. Or maybe the schematics of the test rigs could help.
6. Graph G1: Figure 1, 2, 3, …. The caption and labelling format should match the journal requirements. Normally, it is better to label the data on the graph as much as possible rather the caption. For example, viscosities below the samples, I would not know they are viscosities without looking at the caption. In the graph, the scuffing is indicated with bar charts saying higher is better. But what do these number mean? What is the physical interpretation of the numbers? I’d imagine if I don’t have access to the standard documents, I would not be able to find out the physical meaning of this data.
7. The base fluid SYN is introduced as a reference point in Table 1. It is far later in the text that reader realises it has been used in bearing tests and not in the results for characterisation. Is there a reason SYN characteristics are not compared with other samples in the earlier results?
8. Graph G2: is there a reason the other samples are not investigated?
9. In sentence, “Fluid L is using the same principal base Fluid chemistry as fluid M but using a very different approach to achieve the desired viscosity level, …”, the description of the differences is very vague. Understandably, industry does not want to share confidential information, but could this be explained in more technical terms?
10. Diagram D2: (Figure x, format) what does “B10,GDC5…” mean in the legend? Are these determining statistical parameters or something else? How should the reader know what you are referring to here?
11. Diagram D3: what is the red circle at running time 1 and failure 10? Also, a legend could help to understand the difference between the lines and markers (triangles and circles).

Author Response

Dear reviewer,

Thank you for your prolific response!

We have hopefully fixed the most of your remarks in the last version of our manuscript. Some additional response to the 1. and 5. point:
1. Oil development activities are mostly part of development activities between supplier and customer which are claimed by NDA. So we believe (know) that this activities are in most cases not be published. We add 2 interesting (fundamental) articles to the introduction, were the authors handle the special requirements to develop fluids for e-mobility applications.

5. Yes standards are copyrighted and protected - it is not allowed to publish the standard to third party. We think the reference to the original description (standard number) is better than a condensed form of the method description. We understand the point and were exerted to describe as much as possible.

 

Best Regards

Joerg Franke

Round 2

Reviewer 2 Report

I’d like to thank authors for the few corrections they have implemented. I’m afraid the manuscript still requires major correction. The current state of the manuscript does not provide sufficient report of the methodology to enable research community understanding the underlying physics of the reported results. Please see my following suggestions:

/1/ I recommend authors reviewing the manuscript preparation guidelines on the Lubricants’ website. Structure-wise, authors are not following the standard manuscript format. In scientific papers, there are only figures and figure captions. There are not such variety as pictures, graphs, etc. All illustrations are treated as figures. Introduction accounts for sufficient review of the previous works to clarify the background to the current research and it should not only highlight the significance. Introduction is included in scientific papers to enable early researchers to grasp a good idea of the subject area and how this research is the continuation from previous works. Finally, the list of references at the end still does not follow a standard format and I leave this to the editorial office to check with authors.

/2/ Table 1 can be clarified without breaking the confidentiality for our colleagues in industry. Some indicators as to how samples with the same base fluid and additive packages have different viscosities? There is no scientific or technical evidence in the text by authors as to whether additive packages are meant for friction modification, surface protection, etc. These are very important technical information that differentiates between a technical report and a scientific paper. It is important to researchers to be able to understand what the relationship is between for example measured wear patterns and the nature of additives blended in the lubricants and their percentage. The scientific fundamental discussion in this sense is largely missing and only lubricant behaviour is reported based on Table 1. The current report could be useful to customers and suppliers but not research community.

/3/ Standard tests and the used equipment might be accessible and known to our colleagues in industry, but many researchers might not have access to such details. The manuscript should be sufficiently independent. What were the test and operating conditions? How long the samples were tested for under what load, speed, temperature, … conditions? What is Comb test and what is Cold shift test? Test method: Function, this might be crystal clear in industry but certainly not to the readers. What is the procedure for synchronizer test? What is the definition of OK and not OK in Table 4? How is this description quantified? Is the difference related to the type of additives? What’s the correlation? And so on….

/4/ The discussions around each set of results/figures report the illustrations. What is the underlying physics and reasons for such trends and behaviours? Again, are the differences related to the type and amount of a certain additive in the oils with better performance? These are kind of information that are interesting to the research community and differentiates between a technical report and a scientific analysis.

/5/ Wear tests are not as simple as running a rig and reporting the results. How did authors assess the surface conditions before each test and how did they quantify the growth of wear track and changes in the surface properties? Did they use any interferometry technique to make sure surface changes are monitored during the tests? What was the procedure?

Author Response

Dear Reviewer,

The remarks are listed and answered in the document attached.

We have tried to fixed the open points. 

Best Regards

Joerg Franke

Author Response File: Author Response.docx

Round 3

Reviewer 2 Report

I’d like to thank authors for the corrections they have implemented. I’m afraid the manuscript still requires major correction. The current state of the manuscript does not provide sufficient report of the underlying physics of the findings. Unfortunately, I will have to reiterate the following suggestions:

/1/ Introduction: although it is necessary to cite the standards used in this study, it does not mean review of other research papers should be neglected. Authors should clearly carry out a review of other research papers in this area to highlight the background in the introduction/literature review section.

/2/ Although authors do not wish to reveal the details of the additives, it is common practice to mention the nature of the additives (i.e., friction modifier, anti-wear, anti-foam, etc.). Currently, we only know additive brands are GO-Add and EV-Add and their treat rate. Nothing regarding the physical nature of these additives is presented. Please bear in mind that in a research paper, we are dealing with physics and science. Currently, test results are reported from test machines and there are no analytical discussions around underlying physics as to if authors observe reduction/increase in one property, how this trend is justified in terms of additives, surface characteristics, etc. Clearly, the analytical discussion, which is the foundation of scientific research, is missing in this manuscript. It simply reports which lubricant is better or worse in each test, which is a very commercial approach, not scientific. In scientific approach, we want to know why a certain lubricant is better?

/3/ Wear tests are not as simple as running a rig and reporting the results. How did authors assess the surface conditions before each test and how did they quantify the growth of wear track and changes in the surface properties? Did they use any interferometry technique to make sure surface changes are monitored during the tests? What was the procedure?

There is a high potential in this manuscript, and I will be disappointed if some literature review and the mentioned technical suggestions are not addressed to raise the status of this work.

Author Response

Dear reviewer

thank you very much for the constructive notes regarding the paper. Attached our respond to the several points.

 

Best Regards

Joerg Franke

Author Response File: Author Response.docx

Round 4

Reviewer 2 Report

I would like to thank authors for the clarification of the queries on previous edition. 

There are ways to go round the confidentiality issue by just indicating whether certain e.g. FM is higher or lower in each lubricant without indicating the percentages. This level of information does not breach any confidentiality based on my experience and opens the avenue for more scientific discussions. However, I understand the authors' concerns regarding the confidentiality of their products. 

I believe the manuscript provides interesting information to the scientific community regardless and I would recommend "publish as it is".