Utilization of Waste Cooking Oil via Recycling as Biofuel for Diesel Engines

Round 1

Reviewer 1 Report

This manuscript is od sufficient interest to be accepted for publication, but must first be profoundly modified in its presentation.Thus, references are entered with numbers, but these numbers are not indicated in the corresponding References section. Furthermore, references are only included in the Introduction section. In no other section, such as Experimental, Discussion or Conclusions is any reference made to any bibliographic reference. This gives a completely poor image and lack of scientific rigor, reason why these sections should be improved by introducing references to other works carried out in this same field.

On the other hand, it is necessary to improve the quality of Figures 1, and 6 to 13. In general, the size of the signal pots and lines must be increased.

Author Response

< Reviewer #1’s Comments >

Comments and Revisions: This manuscript is od sufficient interest to be accepted for publication, but must first be profoundly modified in its presentation.Thus, references are entered with numbers, but these numbers are not indicated in the corresponding References section. Furthermore, references are only included in the Introduction section. In no other section, such as Experimental, Discussion or Conclusions is any reference made to any bibliographic reference. This gives a completely poor image and lack of scientific rigor, reason why these sections should be improved by introducing references to other works carried out in this same field.

On the other hand, it is necessary to improve the quality of Figures 1, and 6 to 13. In general, the size of the signal pots and lines must be increased. We also deleted some figures which are not so related to the research and re-arranged the figure list in the updated manuscript.

Reply and revisions: Thank you so much for your thoughtful comment. I would like to make the revision to enter the references with numbers and indicated all the references corresponding to the References section. We also added the references in the other section to reflect our research results with the other research studies. In addition, the quality of Figures 1, 6 and 13 have also improved. All the changes have been highlighted in throughout the manuscript.

Reviewer 2 Report

Reading the title and having a first glance at the abstract it looked a promising paper, as it addresses major issue of the evaluation of waste cooking oil synthetic diesel (WCOSD). I carefully read the article. The topic is highly relevant and fit well into the scope of the “Recycling” Journal. The article is very interesting for the readers of the journal, but a number of improvements have to be made before published. In this light, I suggest a major revision of the article in order to merit publication. I hope that the criticisms I present below in bullet form will help the author improve the paper.

My main objections for publishing the paper in its current form are the following:

• The authors should give a more detailed analysis and clarifications on the methodological advances of the presented approach. I am not completely convinced about the innovation of the methodological approach adopted in the paper.
• Even though the issue addressed by the manuscript is very important the methodology/experimental section (presented in section 2: Experimental apparatus and procedures) proposed is not convincing. In this light, I would suggest the modification of the descriptive of the provided flowchart depicting the major steps of the proposed methodology (Figure 6). The exact flow of the methodology framework that have been utilized within the context of this study is not clear and should be enhanced.
• I would expect more discussion within the justification of the overview of the results.
• In the conclusion’s section, I would expect some more managerial insights and general comments, rather than a repetition of study results. The authors should clearly reconstruct this section.
• As a final comment, I should repeat that the paper needs further explanations. I expect more discussion, more interpretation, based on the above comments. In principal the paper should convince that it does make methodological advances. In conclusion, even though the issue addressed by the manuscript is very important the methodology proposed is not convincing without addressing first the points highlighted above.

Author Response

< Reviewer #2’s Comments > 

1. Reading the title and having a first glance at the abstract it looked a promising paper, as it addresses major issue of the evaluation of waste cooking oil synthetic diesel (WCOSD). I carefully read the article. The topic is highly relevant and fit well into the scope of the “Recycling” Journal. The article is very interesting for the readers of the journal, but a number of improvements have to be made before published. In this light, I suggest a major revision of the article in order to merit publication. I hope that the criticisms I present below in bullet form will help the author improve the paper.

My main objections for publishing the paper in its current form are the following:

The authors should give a more detailed analysis and clarifications on the methodological advances of the presented approach. I am not completely convinced about the innovation of the methodological approach adopted in the paper.

Even though the issue addressed by the manuscript is very important the methodology/experimental Section (presented in section 2: Experimental apparatus and procedures) proposed is not convincing. In this light, I would suggest the modification of the descriptive of the provided flowchart depicting the major steps of the proposed methodology (Figure 6). The exact flow of the methodology framework that have been utilized within the context of this study is not clear and should be enhanced.

Reply and revisions: Thank you so much for your comments. We would like to revise the methodology/experimental section to clarify the problem mentioned by the reviewer. The modification has been highlighted on page 6.

2. I would expect more discussion within the justification of the overview of the results.

In the conclusion’s Section, I would expect some more managerial insights and general comments, rather than a repetition of study results. The authors should clearly reconstruct this Section.

As a final comment, I should repeat that the paper needs further explanations. I expect more discussion, more interpretation, based on the above comments. In principal the paper should convince that it does make methodological advances. In conclusion, even though the issue addressed by the manuscript is very important the methodology proposed is not convincing without addressing first the points highlighted above.

Reply and revisions: Thank you so much for your very thoughtful comments. We appreciate your suggestion and reconstruction of the discussion section and conclusion according to your comment. Once again, thank you so much for your kind and proper comments.

Reviewer 3 Report

Remarks

Title: “… waste cooking oil to its recycling …”

Abstract: lines 21-29 not clear/conflicting and can be summarized (torque and power characteristics).

Introduction: some statements are questionable

Which is the goal of references discussion? Can it be summarized outlining the major points? Bsfc is of course higher, due to the reduction of LHV.

Table 1: were characteristics measured by the authors? Is oxygen not included in biodiesel molecules?

Which are the differences of the proposed WCOSD production method with other manufacturing processes of methyl esters? Which are innovative aspects?

Lines 154-160 are a repetition of previous statements in the same Section 2.

Line 168: caption of Fig.4 is repeated twice.

Experimental campaigns: a figure with the tested operating conditions on the engine operating field would be clearer.

Line 190: what does it mean?

Lines 200-201: which are the percentage variations of torque, power and LHV?

Lines 202-203: if there is a limit on the fuel supply system, the reductions of torque and power are related to this limit, not to the lower value of LHV. Please clarify.

Lines 207-208: parameter showing “how efficiently an engine uses the fuel to produce work” is BTE not bsfc.

Line 208: bsfc is shown in Figure 8, not in Figure 7. Taking into account the reduction in bsfc, it is not clear how it was not possible to achieve the same levels of torque and power when using WCOSD.

Lines 223-225: this statement is not clear.

Lines 228-229: density and viscosity are lower for WCOSD. What about references on variations of BTE and related reasons?

Lines 262-263: what about heat release? Was it calculated from pressure diagrams?

Figures 10 and 11: may the slight differences in coolant and lubricant temperature levels be due to the differences in maximum power/torque (Figure 7)? Generally speaking, when performing tests in steady state conditions coolant and lubricant temperature levels are controlled in order to limit their influence on results. Can it be excluded that observed variations aren’t related to the cooling system behavior and to the uncertainties of measuring equipment?

Lines 283-284: what does it mean that the differences between the temperature levels were inadequate?

Lines 294-295: the discussion is referred to part load conditions, so the comparison is expected to be referred to points with the same levels of torque. What does it mean that “… the CD’s output power was lower than WCOSD’s output power.”?

References are not numbered in their Section.

Author Response

< Reviewer #3’s Comments >

1. Title: “… waste cooking oil to its recycling …”

Abstract: lines 21-29 not clear/conflicting and can be summarized (torque and power characteristics).

Reply and revisions: Thank you so much for your very thoughtful comments. We should indeed be summarized the torque and power characteristics, and thus we revised the manuscript and highlighted in page 1

2. Introduction: some statements are questionable

Which is the goal of references discussion? Can it be summarized outlining the major points? Bsfc is of course higher, due to the reduction of LHV.

Reply and revisions: We already rewrote the discussion section and highlighted throughout the manuscript.

3. Table 1: were characteristics measured by the authors? Is oxygen not included in biodiesel molecules?

Reply and revisions: Thank your for your comment. The oxygen content is the balance one and thus we have not listed in the Table.

4. Which are the differences of the proposed WCOSD production method with other manufacturing processes of methyl esters? Which are innovative aspects?

Reply and revisions: Thank you for your comment. It is beneficial to use transesterification on WCOSD by removing the FFAs from the raw material through neutralization with an alkaline solution, through esterification with glycerine, through extraction with solvents and through distillation or removal of the fatty acids with ion-exchange to avoid the form of soaps. Indeed, to manufacture biodiesel fuel oil in place of diesel with a higher stable energy output than that of the conventional FAME process (60%), the synthesizing process known as the catalytic cracking method (CCM) was used with a non-food oil at the pilot-scale level. An thus, we would like to add this explanation in the manuscript with the highlighted part in page 3.

5. Lines 154-160 are a repetition of previous statements in the same Section 2.

Line 168: caption of Fig.4 is repeated twice.

Reply and revisions: We already revised this issue.

6. Experimental campaigns: a figure with the tested operating conditions on the engine operating field would be clearer.

Line 190: what does it mean?

Reply and revisions: We already revised this Section according to your comment.

7. Lines 200-201: which are the percentage variations of torque, power and LHV?

Reply and revisions: In this research, we measured 3 three times for each test point and calculated the mean value.

8. Lines 202-203: if there is a limit on the fuel supply system, the reductions of torque and power are related to this limit, not to the lower value of LHV. Please clarify.

Reply and revisions: Thank you for your very thoughtful comment. It is this research, we did not modify anything of the supply system and compared it.

9. Lines 207-208: parameter showing “how efficiently an engine uses the fuel to produce work” is BTE not bsfc.

Reply and revisions: Thank you for your comment, we revised this Section and revised on page 8.

10. Line 208: bsfc is shown in Figure 8, not in Figure 7. Taking into account the reduction in bsfc, it is not clear how it was not possible to achieve the same levels of torque and power when using WCOSD.

Reply and revisions: Thank you for your comment, we revised this Section and revise on page 8.

Lines 223-225: this statement is not clear.

Lines 228-229: density and viscosity are lower for WCOSD. What about references on variations of BTE and related reasons?

Lines 262-263: what about heat release? Was it calculated from pressure diagrams?

Figures 10 and 11: may the slight differences in coolant and lubricant temperature levels be due to the differences in maximum power/torque (Figure 7)? Generally speaking, when performing tests in steady state conditions coolant and lubricant temperature levels are controlled in order to limit their influence on results. Can it be excluded that observed variations aren’t related to the cooling system behavior and to the uncertainties of measuring equipment?

Lines 283-284: what does it mean that the differences between the temperature levels were inadequate?

Lines 294-295: the discussion is referred to part load conditions, so the comparison is expected to be referred to points with the same levels of torque. What does it mean that “… the CD’s output power was lower than WCOSD’s output power.”?

References are not numbered in their Section.

Reply and revisions: Thank you for your evaluation. I have been revised all the problems mentioned by the reviewer and highlighted them in pages 9-13.

We appreciate for your helpful comments and do our best to respond. Your comments will be useful information for our future research.

We appreciate your consideration.

Round 2

Reviewer 1 Report

In the process of replacing fossil fuels with others of a renewable nature, it is very important to determine the application limits of current diesel engines, when operating with diesel / biofuel mixtures, in order to make the most of the current fleet of cars, before to carry out the engine modification. Since the work is well done, it can be accepted for publication.

Reviewer 3 Report

Most of the remarks were not considered, especially in the case of results explanation and discussion.

It is not clear why text is highlighted in yellow even if no changes were made.