Effect of Load Priority Modeling on the Size of Fuel Cell as an Emergency Power Unit in a More-Electric Aircraft

Round 1

Reviewer 1 Report

Even though, the work done on the optimization of load shedding and fuel cell size is interesting and the presented results and conclusions are relevant, there are several grammar errors that need to be fixed throughout the manuscript.

The introduction is one long paragraph that is hard to read. The organization of the rest of the manuscript could also be improved. 

Even though the fuel cell hybrid system is proposed as an emergency power unit, there is no mention of safety considerations  of and only cost  and size are use as optimization parameters. Is there anyway to introduce this into the optimization model?

Author Response

1. Even though, the work done on the optimization of load shedding and fuel cell size is interesting and the presented results and conclusions are relevant, there are several grammar errors that need to be fixed throughout the manuscript.

Authors response:

Thank you for your comment. we checked it again grammatically.

2. The introduction is one long paragraph that is hard to read. The organization of the rest of the manuscript could also be improved. 

Authors response:

The introduction is separated into several parts. We checked organization of paper again.

3. Even though the fuel cell hybrid system is proposed as an emergency power unit, there is no mention of safety considerations of and only cost and size are use as optimization parameters. Is there anyway to introduce this into the optimization model?

Authors response:

Thank you for your important comment. it is possible to add some reliability index into the model, but in this paper the only goal was showing the effect of demand side management on the fuel cell operation and size, so we can consider this topic in the future works.

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript describes the optimization study of replacing engine-based electric generator with PEMFC-battery hybrid system.

Overall, the English language contains so many grammatical errors that it is hard to read through and follow the contents. There are also many errors and inconsistencies in style and formatting. Therefore, it is strongly recommended to entirely edit the manuscript to increase the preparedness of the manuscript for further review.

Here is a list of suggestions the authors should pay extra attention during the editing.

1) In the Introduction, the first paragraph is too long. Please divide it to several paragraphs.

2) In line 136, what does "hydrogen power" mean?

3) In line 183 (and some other locations), what is "load critically"? Isn't it "load criticality"?

4) In line 209 (and some other locations), what is the last symbol in equation (11)?

5) In Figure 6, the PEMFC Power first decreases to ~20 at around weighting factor of 0.13, and then increased to reach the asymptotic value of around 30 at weighting factor 0.2. What is the reason for this undershoot?

6) The relation between PEMFC mass and PEMFC power is not clear. For example, in lines 353-354 the PEMFC weighs 800kg for 440kW, while in lines 360-361 the weight of 145kg for 180kW power. In my understanding the fuel cell power is close to proportional to the weight and the volume, but your result is not. Why is it?

Author Response

We would like to appreciate the devoted time and efforts to provide us with constructive comments to improve the technical quality of our manuscript. We have considered all of the comments and our manuscript has been updated to address all of them.

Our responses to comments made by the reviewers are given in the following:

1. In the Introduction, the first paragraph is too long. Please divide it to several paragraphs:

Authors response:

The first paragraph is divided to several paragraphs as you said.

2. In line 136, what does "hydrogen power" mean?

Authors response:

The power that is produced from hydrogen-based fuel cell is hydrogen power. Because hydrogen is input of fuel cell and electric power and water, loss, … are output. Hydrogen power is equal to summation of these output power.

3. In line 183 (and some other locations), what is "load critically"? Isn't it "load criticality"?

Authors response:

Thank you for your comment. Yes it is and it is corrected in the paper on page 8.

4. In line 209 (and some other locations), what is the last symbol in equation (11)?

Authors response:

This symbol is deleted for sake of clarity in the whole locations in the paper.

5. In Figure 6, the PEMFC Power first decreases to ~20 at around weighting factor of 0.13, and then increased to reach the asymptotic value of around 30 at weighting factor 0.2. What is the reason for this undershoot?

Authors response:

It can be said that in normal conditions, the optimum size of the PEMFCS is very sensitive to its cost rises. Because increases in the cost importance more than 20% results in a fixed size of PEMFCS.

6. The relation between PEMFC mass and PEMFC power is not clear. For example, in lines 353-354 the PEMFC weighs 800kg for 440kW, while in lines 360-361 the weight of 145kg for 180kW power. In my understanding the fuel cell power is close to proportional to the weight and the volume, but your result is not. Why is it?

Authors response:

As figure 8 turns out, the relation between PEMFC mass and its power is not linear. Because these two variables are linked by weighting parameter beta. So the cost determines the size (power and weight) of PEMFC.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

In the first round of the review I mentioned

“The manuscript describes the optimization study of replacing engine­based 

electric generator with PEMFC­battery hybrid system. Overall, the English language contains so many grammatical errors that it is hard to read through and follow the contents. There are also many errors and inconsistencies in style and formatting. Therefore, it is strongly recommended to entirely edit the manuscript to increase the preparedness of the manuscript for further review.”

but this comment seemed to be neglected.

Furthermore, the comment (2) in the original review was not reflected in the revision, and the comments (5)(6) were not fully answered based on the physics. 

Therefore, I still think this manuscript needs major revision for the publication.

Author Response

Dear reviewer:

We would like to appreciate the devoted time and efforts to provide us with constructive comments to improve the technical quality of our manuscript. We have considered all of the comments and our manuscript has been updated to address all of them. Also, the authors modified the title of paper to emphasize the more-electric aircraft keyword.

Our responses to comments made by the reviewers are given in the following, the changes are highlighted by Yellow color in the manuscript.

1. The English language contains so many grammatical errors that it is hard to read through and follow the contents. There are also many errors and inconsistencies in style and formatting. Therefore, it is strongly recommended to entirely edit the manuscript to increase the preparedness of the manuscript for further review.

Authors response:

We have carefully edited and proofread the manuscript, like grammatical issues and organization of all sections. Many thanks!

2. The comment (2) in the original review was not reflected in the revision

Authors response:

Based on your suggestion, we have added the hydrogen power definition on page 6.

3. In Figure 6, the PEMFC Power first decreases to ~20 at around weighting factor of 0.13, and then increased to reach the asymptotic value of around 30 at weighting factor 0.2. What is the reason for this undershoot?

Authors response:

Yes.

As can be seen, there isn’t any value between B=0.1 and B=0.2. However, that undershoot is for EXCEL software. Because we had enabled smoothed line in EXCEL for better showing.  The smoothed line is disable for this figure to avoid any ambiguity for readers, as can be seen on page 14.

The output results of the optimization problem for figure 6 are as follows:

4. The relation between PEMFC mass and PEMFC power is not clear. For example, in lines 353-354 the PEMFC weighs 800kg for 440kW, while in lines 360-361 the weight of 145kg for 180kW power. In my understanding the fuel cell power is close to proportional to the weight and the volume, but your result is not. Why is it?

Authors response:

The PEMFC weighs 377 kg for 300 kW not 440 kW. 440 kW is the total amount of interrupted load for B=0 in the mode of three generators outages. We corrected our reporting numbers in the figure 8 on page 17. Based on this figure, the PEMFC mass is 377 kg for 300 kW. Also it is decreased to 225 kg for 180 kW which is highlighted on page 15. As can be seen, the fuel cell power is close to proportional to the weight.

Author Response File: Author Response.pdf

Round 3

Reviewer 2 Report

I think this manuscript is ready for publication.