Mr. Hasan Barkin Nalbantoglu’s master’s thesis focuses on the simulation of a hydrogen fuel cell-powered city bus in a driving cycle. The main objective was to create a simulation model of a fuel cell-powered city bus using the GT-SUITE software.

The text is clear, and the student has successfully described the basic theoretical background of hydrogen, PEM fuel cells, hydrogen storage, fuel cell buses, and electric drive components. The theoretical section provides a broad introduction to the topic. On the other hand, some sections are rather general and descriptive, and a more detailed focus on the modeling methodology itself, energy management strategy, and validation of fuel cell bus models would improve the technical quality of the work.

The practical part of the thesis is based on the development of a model of a city fuel cell bus in GT-SUITE. Key vehicle parameters, such as vehicle weight, hydrogen tank volume, fuel cell power, aerodynamic parameters, and state of charge (SOC) limits, were adjusted according to available public data.

The student conducted a simple optimization study of selected fuel cell parameters, including the number of cells, membrane thickness, active area, diffusion layer thickness, anode and cathode stoichiometry, and channel height. The optimized model reduced the simulated hydrogen consumption in the CHTC-B cycle. The final result is close to the values reported for actual fuel cell buses, but this comparison must be interpreted with caution, as the model has not been experimentally verified.

The main limitation of the work is that the model relies heavily on existing GT-SUITE templates and uses a number of simplified assumptions. The battery and electric motor were not completely redesigned. Their suitability was verified mainly by monitoring vehicle speed and SOC behavior. The energy management strategy is also simplified and uses a constant DC/DC output power demand instead of a realistic control system algorithm. Auxiliary loads, particularly HVAC, were not included as a finely optimized subsystem, which is a relevant limitation for city bus operations.

Another important limitation is the absence of actual experimental validation. The model is compared mainly with general reference values and expected trends.

The optimization method is transparent but relatively simple. The final optimized stack configuration should therefore be interpreted as an optimized case based on simulation under the given model assumptions, not as a directly verified commercial fuel cell design. The author correctly acknowledges this limitation in the thesis.

The formal quality of the thesis is acceptable. The structure is logical, and the figures and tables support the explanation of the model. However, the thesis is relatively short for a master’s thesis, and the discussion of the results could be more in-depth. The text contains repeated grammatical and stylistic errors. While these do not hinder comprehension, they reduce the overall formal quality of the thesis.

Overall, the thesis meets the main objectives of the assignment at a basic to good level. The thesis is not methodologically or scientifically exceptional, and the model has several significant limitations, particularly in the areas of verification, power management, and component sizing. Nevertheless, the thesis contains a complete simulation procedure, and the results are technically comprehensible.

I recommend the thesis for defense and propose an overall grade of C / Good.

Mr. Nalbantoglu’s thesis focuses on the simulation of a fuel cell city bus within a driving cycle and addresses a highly relevant and timely topic. The work begins with a clear explanation of fuel cell principles and different hydrogen production approaches, followed by a description of the model and the results obtained using the GT-SUITE software.

However, the literature review in the first part of the thesis would benefit from greater depth and a broader academic perspective. The entire text is quite brief and could have been significantly expanded. Furthermore, the readability of the thesis would be notably improved with images and graphical explanations; the text does not even include an image of the vehicle being studied. There is also a noticeable tendency to repeat certain pieces of information multiple times throughout the text.

The strongest asset of this thesis lies in its practical application. The student has successfully constructed a functional simulation model and executed a valuable evaluation of various parameter modifications. Through a systematic approach, the author achieved a remarkable optimization goal and provides a clear, insightful analysis of how each modified parameter influences the overall efficiency and hydrogen consumption of the bus. The primary shortcoming of the text remains the limited overall scope of the work. The student used mostly data from GT-Suite database without any further research.

Structurally, the thesis is logically organized, and from a formal standpoint, it meets standard academic requirements. The use of sources is appropriate, the references are correctly cited, and the bibliography includes a sufficient number of recent and reputable scientific publications.

Nevertheless, several typographical and formatting issues are present in the text. For example, isolated articles or prepositions are frequently left at the ends of lines, and numerical values are incorrectly separated from their corresponding units across line breaks. Additionally, the document layout contains unresolved formatting gaps, including abrupt blank spaces on several pages and sequences of disjointed, exceptionally short paragraphs. The list of symbols and abbreviations is completely missing.

In conclusion, the author has delivered a sound thesis that effectively combines theoretical knowledge of fuel-cell vehicles with practical modelling and simulations. Despite the limited scope, I recommend the thesis for defense. Topics for thesis defence:

1. Even though you do not include degradation in your simulation, would your optimization affect the degradation of the fuel cell and how?
2. On page 36, you write: „When the battery SOC reaches the upper limit (SOCmax = 0.85), the extra braking energy is taken by the mechanical brakes.“ Could you explain this SOC limit and why it is used in this kind of powertrain?