Effect of Energy Consumption Reduction on the Decrease of CO₂ Emissions during the Aircraft’s Flight

Round 1

Reviewer 1 Report

Review the Manuscript ID: energies-1174291

Title: Effect of energy consumption reduction on decrease of CO2 emissions during the aircraft’s flight

The aim of the work presented in this paper is to show possible methods to reduce the consumption of energy stored in hydrocarbon fuel during the aircraft flight and the related exhaust emissions into the atmosphere.

The topic covered in the article is relevant.

However:

• The bibliographic review should be improved. Refer results from other studies that used the same methodology or others.
• Review how the acronyms are identified. This question is valid for the entire document.
• Review how units are expressed for different quantities. They should not be between straight parentheses.
• The author should explain the Dijkstra’s Algorithm in more detail.
• Attention, in some situations it uses the point for the decimal part others the comma.
• The author should review the text, especially in section 3. The explanation of the results can/should be improved.

Author Response

Dear Reviewer, thank you for your professional review work on my manuscript. My response to your remarks is presented below. Any changes in the manuscript are made in green font.

Comment 1:

“The bibliographic review should be improved. Refer results from other studies that used the same methodology or others.“

The bibliographic review was improved. The papers cited are included in different parts of the manuscript. The following references were added:

• Baharozu, E., Soykan, G., Ozerdem, M.B., Future aircraft concept in terms of energy efficiency and environmental factors, Energy; 2017, doi: 10.1016/j.energy.2017.09.007
• Filippone, A. Flight Performance of Fixed and Rotary Wing Aircaft. 1st Edition. Butterworth-Heinemann. Elsevier Science & Technology. Oxford. Great Britain. 2006. ISBN: 9780750668170
• Łukasik, B., Analysis of the Posibility of Using Full Electric Technologies for Future Aircraft Propulsion System, in Terms of Mission Energy Consumption, NOx/CO₂ Emission and Noise Reduction, PhD Thesis, Warsaw Institute of Aviation,
• Pilecki, S. Lotnictwo i Kosmonautyka – Zarys Encyklopedyczny (Aviation and Cosmonautics - Encyclopedic Outline). WKL Publ. Warsaw. Poland. 1984. ISBN 83-206-0343-9.
• Rutowski, E. S. ,Energy Approach to the General Aircraft Performance Problem,. Journal of the Aeronautical Sciences (Institute of the Aeronautical Sciences), 1954; 21(3), 187–195. doi:10.2514/8.2956
• Zagalsky, N. Aircraft energy management. American Institute of Aeronautics and Astronautics. 11th Aerospace Sciences Meeting. Washington, DC, U.S.A. (10-12 January 1973). doi:10.2514/6.1973-228.

Unfortunately, there are not many current research concerning the energy methods I could refer to. It should be noted that energy methods or energy approaches were mainly used in terms of performing maneuvers, such as take-off or climb, in fighter aircrafts. Currently, e.g., [Kuźniar 2021; Lukasik 2017] the energy approach to flight is becoming increasingly interesting, because in the era of the development and application of different propulsion, this method can be used to compare various aircraft design systems, even those that are equipped with hybrid or purely electric propulsion. And this will constitute a further direction of my research.

Comment 2:

Review how the acronyms are identified. This question is valid for the entire document.

         All acronyms were revised.

Comment 3:

Review how units are expressed for different quantities. They should not be between straight parentheses.

I agree. The parentheses […] were replaced by (…), e.g.  – drag force (N)’; or omitted, e.g. ‘ = 239.5 m/s.’

Comment 4:

The author should explain the Dijkstra’s Algorithm in more detail.

I agree. The section containing the explanation of the Dijkstra’s algorithm (a few paragraphs under fig. 5) was expanded.

Comment 5:

Attention, in some situations it uses the point for the decimal part others the comma.

I agree.  was replaced by . I also verified the manuscript in case there were any similar mistakes.

Comment 6:

The author should review the text, especially in section 3. The explanation of the results can/should be improved.

I agree with the remark, the text was revised. All changes made are given in green. Due to the fact that the 2nd variant (describing the possibility of using a hybrid system based on two marching jet engines with an additional fan driven by an electric motor to reduce energy and emissions) is under evaluation,  Sections 3 and 4 were rebuilt – discussion concerning hybrid propulsion was removed from section 3 and added to section 4 as the future course of action for the research. Moreover, the concept concerning the hybrid propulsion was better explained and referred.

Reviewer 2 Report

For the abstract; 

1-''The Boeing 737 with Snecma CFM 56C engines was selected for the research.''Extensive English check.

2-''the second variant, the possibility of using a hybrid system based on two  marching jet engines with an additional fan driven by an electric motor was tested in terms of energy  and emission reduction.''This concept is still under evaluation and requires extensive optimization and analyses. It is too early to consider this as an option to build your case of study upon.

3-Methodology: very general. The authors are advised to have a look at the preliminary aircraft design books and references, where a more detailed methodology is provided. 

4-For wind speed in a given i-segment of the cruise phase, How are you planning to quantify this value? This requires extensive and sufficient statistical analyses over wide geographical and time intervals. 

5- Paper's structure and presentation; very poor presentation. The author is advised to follow the conventional academic writing style (i.e.; those adopted by Energies)

Although the paper requires extensive amendments, I still see good potential in the paper. Therefore, I will recommend major corrections and I hope the authors submit their revised paper with significant amendments. 

Good Luck.   

Author Response

Dear Reviewer, thank you for your professional review work on my manuscript. My response to your remarks is presented below. Any changes in the manuscript are made in green font.

Comment 1:

“The Boeing 737 with Snecma CFM 56C engines was selected for the research.'' Extensive English check.

The sentence indicated was replaced by:

“The Boeing 737 aircraft equipped with Snecma CFM 56C engines was adopted for the research.”

I hope it sounds better.

I reviewed the whole text and corrected grammar, style and punctuation mistakes. If this is not satisfactory, I could submit the final version of the manuscript for English editing.

Comment 2:

''the second variant, the possibility of using a hybrid system based on two marching jet engines with an additional fan driven by an electric motor was tested in terms of energy and emission reduction.'' This concept is still under evaluation and requires extensive optimization and analyses. It is too early to consider this as an option to build your case of study upon.

I absolutely agree with the remark and have decided to change this part of section 3 in such a way that all discussion concerning hybrid propulsion was removed from that section and transferred, with some modifications, to the discussion section as a future course of action for the research.

Comment 3:

Methodology: very general. The authors are advised to have a look at the preliminary aircraft design books and references, where a more detailed methodology is provided.

In my opinion, the described methodology is sufficient to conduct the research and obtain results.

In the research, I did not focus on the design of the aircraft, but only on its performance. In Section 2, I added some essential information that was missing - a method of determining the performance of the aircraft on the basis of the literature.

Comment 4:

For wind speed in a given i-segment of the cruise phase, How are you planning to quantify this value? This requires extensive and sufficient statistical analyses over wide geographical and time intervals.

In the research conducted, I was basing on available weather forecast data retrieved from windy.com. Of course, such data can be retrieved from other sources. The access to such data is not a problem, however, it can be not for free, as it is in the case of some options of windy.com.

In my research, I focused on the method of determining the trajectory based on the available weather data (wind speed and direction) forecasted for a given date and time. This data is necessary for further calculations –to determine the value of all graph edges – using formula (6).

Comment 5:

Paper's structure and presentation; very poor presentation. The author is advised to follow the conventional academic writing style (i.e.; those adopted by Energies)

Thank you for this remark, the manuscript was revised and in weak points, according to the reviewers’ comments – improved. All changes are given in green font. I reviewed the whole text and corrected grammar, style and punctuation mistakes. If this is not satisfactory, I could submit the final version of the manuscript for English editing.

Reviewer 3 Report

This manuscript title, Effect of energy consumption reduction on the decrease of CO2 emissions during the aircraft’s flight, is written to give insight into reducing CO₂ emissions for Boeing 737 aircraft discussing two approaches, i.e., optimal trajectory and hybrid propulsion. This is an interesting topic. However, this manuscript requires some revisions before it can be accepted. My specific comments for the manuscripts are as follows:

 The abstract is well summarized. However, in line 18, the last sentence of the abstract uses the words “more” and “further” in the same sentence, which is not appropriate. It should be revised.

1. The authors should clearly explain the significance and impact of the work. The novelty of the work is not clear. More data and discussion are required. 
2. The last paragraph of the introduction section should include details about how the current study is novel from previous studies?
3. Variant 1 in the study shows that energy consumption and CO₂ emissions are reduced by 10% using Trajectory 4. However, my main concern is how this claim would be interpreted in the actual case, as the present results are based on a theoretical model. Can the author compare the results with experimental data so the accuracy of results should be verified? Furthermore, the optimized trajectory doesn’t account for other emissions such as NO_x, SO_x. How can the author justify that only 10% reductions in CO₂ would be beneficial for the actual scenario?
4. The 2^nd approach discussed by the researcher does not present any substantial results. In my opinion, it shouldn’t be a part of the current study as authors have merely discussed the hybrid approach as a possible concept. It would be more feasible if authors could add the hybrid propulsion as a future course of action for the research in the conclusion section.
5. The conclusion needs to be further summarized, and the study's important findings should be written in bullet forms.

Author Response

Dear Reviewer, thank you for your professional review work on my manuscript. My response to your remarks is presented below. Any changes in the manuscript are made in green font.

Comment 1:

The abstract is well summarized. However, in line 18, the last sentence of the abstract uses the words “more” and “further” in the same sentence, which is not appropriate. It should be revised.

I see your point, but in my humble opinion the entire sentence “The concept is promising, but requires more detailed further research” is correct - the parts indicated: “more detailed” is correct, as this is the comparative form of the adjective “detailed”; and “further research” is correct, because “further” is the adjective “far” in the comparative form and “research” is an uncountable noun. The whole part means that more detailed (or profound) research is required and it will be conducted further on, hopefully.

Comment 2:

The authors should clearly explain the significance and impact of the work. The novelty of the work is not clear. More data and discussion are required. 

I agree with the suggestion: “The authors should clearly explain the significance and impact of the work. The novelty of the work is not clear.” Therefore, I have decided to add in the manuscript the following paragraph explaining and underlining the novelty of the research conducted:

“The novelty of the research described in the paper is the use of the energy approach and tying the energy parameters of the aircraft to the flight duration and pollutants emission in the cruise phase.”

If we are able to properly manage the energy stored on board and are able to properly plan the flight trajectory on a given route, the aircraft will consume less fuel and the emission will be lower. This is beneficial, both from the economic and from the environmental point of view.

However, I do not see clearly which “more data and discussion are required”. Based on the data I had, all computations I needed to make, were made. The results obtained allowed to present the concept of using the energy approach to calculate the energy required for flight and to determine the’ best’ (the most sustainable in terms of the adopted criteria), the flight trajectory of the aircraft in the cruise phase.

Discussion Section was improved, taking into account your and other reviewers’ comments.

Comment 3:

The last paragraph of the introduction section should include details about how the current study is novel from previous studies?

I agree with the comment. I added the following text:

“Previously conducted studies did not include an energy approach at all. A novelty in relation to earlier research is tying the energy consumption of the aircraft to the pollutants emissions and flight duration.”

Comment 4:

Variant 1 in the study shows that energy consumption and CO₂ emissions are reduced by 10% using Trajectory 4. However, my main concern is how this claim would be interpreted in the actual case, as the present results are based on a theoretical model. Can the author compare the results with experimental data so the accuracy of results should be verified? Furthermore, the optimized trajectory doesn’t account for other emissions such as NO_x, SO_x. How can the author justify that only 10% reductions in CO₂ would be beneficial for the actual scenario?

Unfortunately, it is not possible to carry out direct pollutant emissions measurements for an aircraft during the flight. The studies determining the emissions in flight are theoretical (computational) studies, based, as in this manuscript, on the actual emission indices (EIs) available in the ICAO database. In my previous research and previous papers, I described the method of determining the emissions of various pollutants (CO, CO₂, NOx, HC) using the emission model I developed, but in this manuscript I focus on other research issues – tying the energy stored on board the aircraft to the pollutant emissions and flight time.

Answering the question: "How can the author justify that only 10% reductions in CO₂ would be beneficial for the actual scenario?", it should be noticed that the 10% reduction in emissions can be considered very big and very satisfactory. It is widely recognized that even a few percent is a very good scenario.

 Comment 5:

The 2^nd approach discussed by the researcher does not present any substantial results. In my opinion, it shouldn’t be a part of the current study as authors have merely discussed the hybrid approach as a possible concept. It would be more feasible if authors could add the hybrid propulsion as a future course of action for the research in the conclusion section.

I absolutely agree with the remark, and I have decided to change this part of section 3 in such a way that all discussion concerning hybrid propulsion was removed from that section and added to the conclusion section as a future course of action for the research.

Comment 6:

The conclusion needs to be further summarized, and the study's important findings should be written in bullet forms.

I improved this section – Discussion. Some information referring to your previous remarks, such as comment number 2 and number 5, is included as well.

However, I think that the bullet form in the case of this manuscript is not necessary, as the discussion is clearly divided into paragraphs.

Round 2

Reviewer 1 Report

Review the Manuscript ID: energies-1174291- v2

Title: Effect of energy consumption reduction on decrease of CO2 emissions during the aircraft’s flight

The aim of the work presented in this paper is to show possible methods to reduce the consumption of energy stored in hydrocarbon fuel during the aircraft flight and the related exhaust emissions into the atmosphere.

The topic covered in the article is current and relevant.

The review/correction performed by the authors allowed an improvement in the quality of the paper.

The author should review the text.

Author Response

Dear Reviewer,

Thank you very much for your all remarks and suggestions. After corrections my manuscript looks much better and more professional. I removed the Figure 1, according to the Reviewer’s #2 suggestions, and, as you suggested, made some more corrections (English check) - I have highlighted them with yellow. I used the programme (the licence was ordered by my university) and went through the text once again. I hope it is OK now.

Kind regards, 
Małgorzata

Author Response File: Author Response.pdf

Reviewer 2 Report

The authors have addressed all the required comments from my previous report successfully. I recommend accepting the paper in the present form. 

Only one comment; please replace figure 1 with a more professional sketch. Otherwise, remove it. It is too  general. 

Good Luck. 

Author Response

Dear Reviewer,

Thank you very much for your all remarks and suggestions. After corrections, my manuscript looks much better and more professional. I have decided to remove the Figure 1, as you suggested, and made some slight corrections (English check) - I have highlighted them with yellow.

Kind regards,
Małgorzata

Reviewer 3 Report

All the suggestions have been incorporated and I recommend the revised manuscript for publication. 

Author Response

Dear Reviewer,

Thank you very much for your all remarks and suggestions. After corrections my manuscript looks much better and more professional. I have decided to remove the Figure 1, and made some slight corrections (English check) - I have highlighted them with yellow.

Kind regards,
Małgorzata