Current Knowledge on Friction, Lubrication, and Wear of Ethanol-Fuelled Engines—A Review

Round 1

Reviewer 1 Report

The authors conducted a review on the state of lubrication system in an ethanol-fuelled engine. They covered the tribological challenges faced by the engine lubrication system when fuelled with ethanol-based fuel. Discussions on the gap and recent triblogical advancements in overcoming the mentioned deficiencies of present lubricants are also included.

Overall, the review is interesting and useful to the automotive industry, especially when most attention is on electrification. There are only a few things that can be improved as given below:

Comment #1:

Please highlight the significant findings from the review in the abstract.

Comment #2:

Please clearly indicate the operation limit of the lubricant in Figure 1. Is it in the middle part (orange colour?) or the front part of the regimes indicated? 

Author Response

Comment #1:

Please highlight the significant findings from the review in the abstract.

Thanks for the suggestion, we have extended the abstract, adding the main findings from the review.

Comment #2:

Please clearly indicate the operation limit of the lubricant in Figure 1. Is it in the middle part (orange colour?) or the front part of the regimes indicated? 

Good suggestion, we have added the operation limits both in absence and presence of ethanol, showing then how ethanol reduces the operation limit of the engine.

Reviewer 2 Report

This is an excellent review paper relevant to the special issue of Current and Future Trends in Tribological Research. The review is quite informative and readable for every tribologist. One comment to improve this paper is that Figure 3 (b) to (e) are too compressed to read legend and pictures, although the illustration is good for readers. If possible, the sizes of legend and axis index terms should be increased in Figs. 4, 5 and 6. This review is recommended to publication after the minor revisions.   

Author Response

This is an excellent review paper relevant to the special issue of Current and Future Trends in Tribological Research. The review is quite informative and readable for every tribologist. One comment to improve this paper is that Figure 3 (b) to (e) are too compressed to read legend and pictures, although the illustration is good for readers. If possible, the sizes of legend and axis index terms should be increased in Figs. 4, 5 and 6. This review is recommended to publication after the minor revisions.   

Thanks. This is a difficult task because the amount of information in each figure is very large. However, we agree with the reviewer and tried to improve them as much as possible.