Tribological Performance for Steel–Steel Contact Interfaces Using Hybrid MWCNTs/Al2O3 Nanoparticles as Oil-Based Additives in Engines
Round 1
Reviewer 1 Report
The manuscript is written very well. Few comments are mentioned below.
1. Abbreviations should be explained of their first mention.
2. Lots of similar works have already published [example ref. 58, 59]. So, the study has lack of novelty.
3. Write ‘additive free lubricant sample’ instead of ‘free lubricant sample’.
4. What is the chemistry of oleic acid to act as a stabilizing agent or to keep homogeneity of the lubricant solution?
5. Explain the eq. 1 more clearly.
6. Please give a graphical abstract of the study.
7. In the conclusion the significance of the study should be explained rather mentioning the experimental results.
Comments for author File: 
Comments.pdf
Author Response
The authors would like to thank the editor and reviewers for giving us the opportunity to submit a revised draft of the manuscript “Tribological performance for steel-steel contact interfaces using hybrid MWCNTs/Al2O3 NPs as oil-based additives in engines” for publication in the Fluids. We appreciate the time and effort that you and the reviewers dedicated to reviewing and analyzing our manuscript and are grateful for the valuable comments and useful remarks to our paper. We have considered most of the suggestions made by the reviewers. Those modifications are highlighted in the manuscript. Please see below, for a point-by-point response to the reviewers’ comments and concerns.
1. Abbreviations should be explained at their first mention
Response: Thank you for pointing this out. We have modified this point.
Multi-walled carbon nanotubes (MWCNTs) - Scanning electron microscopy (SEM) - Coefficient of friction (COF) - X-Ray Diffraction (XRD)
- Lots of similar works have already been published [example ref. 58, 59]. So, the study has lack of novelty
Response: The reviewer has addressed a very important point in terms of similarity with some previous publications
[58] A. K. Sharma, A. K. Tiwari, A. R. Dixit, and R. K. Singh, “Measurement of machining forces and surface roughness in turning of AISI 304 steel using alumina-MWCNT hybrid nanoparticles enriched cutting fluid,” Measurement, vol. 150, p. 107078, 2020.
[59] B. Sahoo, D. Narsimhachary, and J. Paul, “Surface mechanical and self-lubricating properties of MWCNT impregnated aluminium surfaces,” Surf. Eng., vol. 35, no. 11, pp. 970–981, 2019.
Initially, the aforementioned researchers agree with the authors' idea of using a filler that contains a pair of raw materials that contribute to a more effective role in improving fluid properties. However, they differ in the method of processing, handling and application. In both papers, the cooling oils used in machining and their effects on the quality of the surfaces of the products were studied. The current study aims to improve the properties of engine oils, which is a major problem for energy loss and equipment life. The authors used hybrid nano-additives composed of MWCNTs and Al2O3 NPs to exploit the unique properties of both materials. The study was conducted to evaluate the performance of the nanolubricants under various operating conditions, loads, and temperatures. High temperatures pose a major challenge as oils lose much of their viscosity, which increases the wear rate. However, the nanolubricants used clearly helped improve the performance of the oils at these temperatures.
- Write ‘additive free lubricant sample’ instead of ‘free lubricant sample’.
Response: All of them were modified
- What is the chemistry of oleic acid to act as a stabilizing agent or to keep homogeneity of the lubricant solution?
Response: Oleic acid is a monounsaturated omega-9 fatty acid found in various plants and animals. It has the formula CH3(CH2)7CH=CH(CH2)7COOH. Oleic acid used as a surfactant, which confirmed to stabilize suspension and dispersion the nanofillers in oil. Oleic acid has an active group and a long alkyl chain containing about 16 carbon atoms. These surfactants were used to directly modify nanoparticles’ surfaces.
- Explain the eq. 1 more clearly.
Response: The revised text is illustrated on [page 5].
The wear rate of tested steel block is estimated based on the following relationship:
|
(1) |
Where, ΔV is the accumulative lost volume of tested steel block, mm3. Which can be estimated the relation of Δm/ ρ. So, ∆m is the weight loss, gm, was determined via weighing the steel block before and after the test. And ρ the steel density, gm/mm3. Fn is the normal force and L is the total sliding distance recorded during the test.
- Please give a graphical abstract of the study.
Response: Done
- In conclusion the significance of the study should be explained rather than mentioning the experimental results.
Response: The revised text is illustrated on [page 13].
Finally, based on the results, it is recommended to effectively use the hybrid nanofiller Al2O3/MWCNTs for engine oil, 10W-30, at high operating temperatures. Moreover, the loading amount of 2.0 wt% of Al2O3/MWCNTs, with a ratio of 1:1, is the optimum dispersion amount.
Reviewer 2 Report
Please see attached report
Comments for author File: Comments.pdf
Author Response
The authors would like to thank the editor and reviewers for giving us the opportunity to submit a revised draft of the manuscript “Tribological performance for steel-steel contact interfaces using hybrid MWCNTs/Al2O3 NPs as oil-based additives in engines” for publication in the Fluids. We appreciate the time and effort that you and the reviewers dedicated to review and analyze our manuscript and are grateful for the valuable comments on and useful remarks to our paper. We have considered most of the suggestions made by the reviewers. Those modifications are highlighted in the manuscript. Please see below, for a point-by-point response to the reviewers’ comments and concerns.
Reviewer comments:
- The paper lacks correlation findings, for example, why the authors didn’t consider finding correlations that incorporate the temperature, friction coefficient, and kinematic viscosity. I believe this will make the paper more thorough and concise.
Response: On this point, the authors believe that the correlation between temperature, viscosity and wear rate is an integral part of the concept of lubrication. Therefore, to study the efficiency of engine oil, it must be done by covering these aspects. Therefore, the current work aims to improve the properties of the oil using nanotechnology.
- The introduction literature doesn’t cover the nanoparticle dispersions applicability of the nanoparticles in other fields such as hydrodynamics and heat transfer: doi.org/10.1038/s41598-021-95269-z / doi.org/10.1007/s10665-021-10205-4 where results have a major impact on the tropological performance in terms of slip mechanism and kinematic viscosity contribution to heat cooling.
Response: Done
The revised text is illustrated on [Ref 36 page 2, and Ref 37 page 2].
Nanoparticles (NPs) have an active role in heat transfer that leads to enhance the tribological mechanism under heating-loads boundary conditions [35]. The nanoparticle dispersion on the oils has a major impact on cooling and lubrication applications that contribute to improving the heat transfer and fluid kinematic viscosity [36, 37].
- The author stated, “Each experiment was repeated five times, and a standard deviation was shown” No statistics have been reported in this context. Please clarify.
Response: The study is carried out by measuring the values of the tests five times under the same conditions and calculating the average value to ensure the accuracy of the displayed results.
- The authors stated “The wear mechanism was performed under different working conditions” could you be more precise about the “working conditions”
Response: The working conditions are explained in the text on page 4
The tribometer is equipped with speeds of 500, 1000, 1500, 2000, and 2500 rpm at a load of 200 N. The samples were tested at temperatures of 50, 75, and 100 °C to simulate operating conditions.
- Section 2 experimental setup: please elaborate more on the settings setup and add a photo if available.
Response: The graphical abstract was added in the text on page 1
- Figure 1 (C) please comment more on the figure it is not clear what to understand from it. Need to define the acronym XRD and explain what to maintain from this figure.
Response: The acronym XRD was modified to X-Ray Diffraction (XRD) and the XRD analysis was displayed in the text on page 3
The XRD pattern of Al2O3 NPs is indicated diffraction peaks were centered at 2θ of 32.7°, 39.6°, and 63.7°, which may be evident to the crystal planes. While XRD analysis for MWCNTs exhibits a diffraction peak located at 2θ of 26.5° that is evident to the presence of carbon. While XRD pattern exhibits peaks with low intensity.
- Page 9: “the worn contact surfaces of the nano lubricant samples was shown in Figure 8” Please say were shown in Figure 8. Similar grammar typos are across the manuscript.
Response: The original text “For better illustration, the topography of the worn contact surfaces of the nano lubricant samples was shown in Figure 8” is correct
- Many acronyms are not defined when they first appear in the text. Please check all text.
Response: We have modified this point.
Multi-walled carbon nanotubes (MWCNTs) - Scanning electron microscopy (SEM) - Coefficient of friction (COF) - X-Ray Diffraction (XRD)
- Figure 10: Please. Make bigger, use more space, and if possible, give better quality images.
Response: Figure 9 was modified.
Round 2
Reviewer 1 Report
Comments:
1. 1. Write the full form of NPs of its first mention. .
2. 2. In the last point of the conclusion, the author should not mention the number (5). Because it is the consequence of the point no.4. The author should write simply the lines like that ‘Based on the results, it is recommended that the hybrid nanofiller (Al2O3/MWCNTs) for engine oil 10W-30 can be used effectively at high operating temperatures. Moreover, the loading amount of 2.0wt% Al2O3/MWCNTs with a ratio of 1:1 is the optimal dispersion amount.’
Comments for author File: Comments.pdf
Author Response
changes required were made and highlighted in yellow
Reviewer 2 Report
I have read the revised manuscript which shows great improvement from the first version. The authors answered all my concerns and I feel comfortable recommending this paper for publication in its current version.
Author Response
many thanks
