From a Battery-Based to a PEM Fuel Cell-Based Propulsion Architecture on a Lightweight Full Electric Aircraft: A Comparative Numerical Study

Round 1

Reviewer 1 Report

The investigation addresses the preliminary design of a fuel-cell-based powertrain for an eVTOL. The novelty of the investigation is limited and not clearly explained in the introduction where the state of the art in this topic is not sufficiently described. 

As for the scientific rigor, the adopted methodology is based on a commercial software that was used also to obtain the models for the components of the powertrains. Therefore, no validation or development of new models is proposed. Nevertheless, given the relevance of the topic, the paper could be accepted after revising it. These are the modifications that need to be made:

1) the abstract does not reflect the content of the paper. In fact, there is no mention of the use of supercapacitors.

2) Introduction.

2.1) Please improve the description of the state of the art about the methodologies adopted for the sizing of fuel-cell based powertrains

2.2) put into evidence the novelty of the proposed approach; 

2.3)  check the sentence at line 27 of page 1. Energy density is referred to hydrogen (energy carrier) not to fuel cell (converter)

3. Description of the propulsion system. Any assumption about the specification of the components of the powertrain should be accompanied by a reference or justified. See for example the GI of hydrogen storage that is assumed equal to 0.1.

4) Numerical model. The authors should address the topic of fuel cell dynamic response and how this must be taken into account in the development of the energy management strategy (see Optimized Energy Management Strategy for Hybrid Fuel Cell Powered Drones in Persistent Missions using Real Flight Test Data, IEEE Transaction on Energy Conversion, 2022)

5) Results and discussion. The authors use a very simple energy management strategy using the power level as the only rule.  A comparison of the proposed control strategy with existing approaches is missing, with particular reference to the role of the supercapacitor... why the supercapacitor was used only for the first spike of power in the power request of fig 15 and not for the second one?

 

6) Conclusions. Some of the statements reported in the conclusions section are not supported by the results shown in the paper:  “The application of the models on the abovementioned architectures has allowed us not only to examine the issues of energy management but also to evaluate the importance of the dynamic phenomena. In addition, being the models parameterized, several simulations have been launched from which it emerges that also small aircraft like a motor glider could take advantage of hydrogen-powered architectures” and “Several other aspects of the latter proposed architecture have also been investigated: for example, the possibility of recharging the battery pack when the fuel cell stack provides low power. These results, together with many others, are not covered by this article since they are deemed out of topic.” Which is the actual topic addressed in this paper? The modeling approach, the sizing procedure, the energy management strategy?

 

 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper gives a clear and well-structured insight into the simulation of alternative propulsion systems. I have only a small number of mainly minor comments to the authors which are listed in the following:

- Line 128 (minor): "... the total mass of the hydrogen supply system ..."

- Figures 2 & 13 (minor): font sizes too small, graphic quality insufficient

- Figure 3 (minor): abbreviation "OCV" used but not explained nor listed in the list of abbreviations

- Line 156f (minor): "As mentioned in a previous section, the architecture of the battery pack for the battery based propulsion system consists of 154 cells in series with 12 strings in parallel ..." --> no, this is not mentioned before.

- Line 189 (minor): abbreviations "PMSM" and "BLDCM" used but not explained nor listed in the list of abbreviations.

- Table 2 (minor):

   # abbreviations "VHML" and "MVAC" used but not explained nor listed in the list of abbreviations

   # for clarity: "Table 2. Parameters of the air-cooled EMRAX 268 VHML MVAC motor at 200 rev/min.

- equation (7) (MAJOR): air density rho missing in drag formula!

- line 219 (minor): "Propeller has been modeled after McCormick (1979) ..." --> this report should be part of the list of references.

- Figure 7 (minor):

   # what is the added value of showing two identical sets of graphs?

   # is "Mach" a reasonable speed measure in this case?

- Line 321 (minor): "The x-axis scale has been enlarged for the start of the mission ..." Figure 14 has no x-axis.

- Reference 27 (minor): the "7." in front of the authors might be obsolete.

 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors addressed all my comments. The paper can be published in the present form.