Applications of Oxyhydrogen, Direct Water Injection, and Early-Intake Valve Closure Technologies on a Petrol Spark Ignition Engine—A Path towards Zero-Emission Hydrogen Internal Combustion Engines
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe paper presents an innovative approach to achieving zero-emission hydrogen internal combustion engines (H2-ICEs) by applying oxyhydrogen combustion, direct water injection, and Early Intake Valve Closure (EIVC) technologies. It demonstrates that transitioning to hydrogen fuel with pure oxygen combustion significantly reduces emissions. The study validates the baseline model against experimental data, showing good alignment. The application of water injection effectively manages cylinder and exhaust temperatures, while EIVC technology enhances engine efficiency and performance.
The authors performed a comprehensive validation of the baseline model ensures reliability. An innovative integration of oxyhydrogen combustion with water injection and EIVC for emission reduction and a detailed analysis of performance improvements and temperature management.
The scalability of the proposed solutions to larger or commercial engine applications is not discussed.
The economic and practical feasibility of sourcing and storing pure oxygen for combustion needs clarification.
How do the high cylinder temperatures in oxyhydrogen combustion models affect long-term engine durability and material integrity?
Can the proposed technologies be effectively scaled up for commercial and industrial engine applications?
What are the economic implications of using pure oxygen for combustion in terms of sourcing, storage, and overall operational costs?
How does water injection influence the overall efficiency of the engine, considering the thermal management benefits?
The quality of the figures is very low.
The paper is to be checked for misprints and grammatical errors.
Comments on the Quality of English LanguageThe paper is to be checked for misprints and grammatical errors.
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for Authors
Review of the submitted paper entitled "Applications of Oxyhydrogen, Direct Water Injection, and EIVC Technologies on A Petrol SI Engine – A path towards zero-emission H2 - ICEs".
Review Comments
The paper presents a simulation study on the utilization of oxy-combustion, direct water injection and Miller cycle Early Inlet Valve Closing (EIVC) in a Spark Ignition (SI) engine fueled by hydrogen. Simulation has taken place through commercially available Realis WAVE software and its accuracy was verified through experimental results published in literature. The subject matter of the paper is suitable for publication in the Energies Journal and also, the work, as far as I know, is original. The abstract is informative and the discussion adequately detailed.
I suggest the acceptance of the paper after Minor Revision.
My comments are as follows:
1. The use of English can be improved. I suggest editing by a native English speaker. Some paragraphs are not well written or are not understandable. Some examples are paragraphs in Lines 135-138, 255-257, 323-325, 445-451.
2. The authors provide a list of Abbreviations but some of the abbreviated terms are not explained. For example, CI (for Compressed Ignition) is not explained anywhere. Also, I believe that despite the addition of the Abbreviation list, the terms must be explained in the text when they are introduced for first time. This will improve the readability of the manuscript.
3. Lines 88, 92, 134, 144, 147, 163, 166 should not begin with a capital letter and should be appropriately aligned in the left margin of the manuscript.
4. The word “increasement” is rarely used in English. I suggest that the authors will correct it with other appropriate words such as “increment”, “growth” etc.
5. Line 31. Correct the phrase “…attracted huge amounts of engineer’s and scientists’ attentions” with something simpler and less exaggerated.
6. Lines 37-42. The authors confuse the reader when they speak about the utilization of carburators and gasoline injection. Please describe better the difference of these systems and when they are employed.
7. Equation (1) mentions an enthalpy change of -44.27 kJ/g but the text which follows mention an enthalpy change -47.87 kJ/g. Which is the correct amount?
8. Don’t write the units of numbers in italics. Correct in the entire manuscript.
9. Line 103. I suggest to correct the word “keeps” by “remains”.
10. The description of the Miller Cycle in Section 2.2. needs improvement. In Lines 101-107 please mention at what point of Figure 1 the inlet valve opens and closes (point 1a?) and how this is accomplished technically (special valve mechanism?). Also, describe better what do you mean by “blow back” effect and why it increases engine efficiency.
11. Line 118. Erase the word “structure”.
12. Line 121. A reference number is required after mentioning the work of Knaus et. al. Also, this work is not listed in the References.
13. Line 144. Change “length” by “diameter”.
14. Symbols in equation are different by the same symbols in the text. For example, in Line 144 symbols D, P and T must be corrected to be identical with those in Equation (5). Make the same correction in the entire manuscript.
15. Line 145. Explain the role and the assumed value for Cenht.
16. What are the reference temperature and reference pressure mentioned in line 147?
17.Which are the heat transfer coefficients assumed equal to 1? Lines 150-151 are not understood and can be misleading.
18. Line 166. Better define the angles theta_0 and theta_i in terms of CAD.
19.Figure 5a explains the EIVC scenarios examined in the study but one sees that both inlet valve closing timing and inlet valve lifting are changed simultaneously. Why did both parameters change simultaneously and upon what criretia? The effect of EIVC does not change when the valve lifting change at the same time? How one can isolate the two effects on the engine performance in such a way? Is the change of lifting inevitable when the valve timing changes? If so, why? Please explain these issues appropriately.
20. The symbol of hour in the SI system is “h” and not “hr”. Please correct appropriately in the entire manuscript.
21. Line 210. I believe that you have to correct into “….data exhibit downward trends at higher speeds”.
22. Place spaces before parentheses in Lines 272 and 278.
23. Lines 277-280. Which are these temperatures during the exhaust stroke? Are they average values? Please explain.
24. Hydrogen is known to have much higher flame velocity than gasoline. How does this affects the engine performance? For example does it have an impact on temperature or pressure increase rate? Why this is not observed in Figures 10a and 10b?
25. Line 309. Please rewrite the sentence to become understandable.
26. Line 348. Correct into “….temperatures are all above…”.
27.Line 355. Correct into “…charges and, thus, the cylinder…”
28. Please define the term “extent of early intake valve closure”. How is mathematically defined as a percentage value? Also, is there any correlation between this and the expansion ratio?
29. Line 378. Change “reduction” by “closure”.
30. Line 405. Correct as “….increases by 35.86%....” or appropriately.
31. Line 419. Correct the word “except”.
32. Line 423. Correct the word “model”.
33. Line 427. Correct as “At the rotational ….”.
34. Line 431. Correct into “….torque produced…”.
35. Line 437. Correct into “…8500 rpm.”.
36. The presentation and discussion of the Conclusions in Section 4 must be improved. Please make a better presentation of the results with clear and simple sentences. The presentation through bullet points and then through many “:” does not help the reader. Improve use of English.
Comments on the Quality of English Language
Review of the submitted paper entitled "Applications of Oxyhydrogen, Direct Water Injection, and EIVC Technologies on A Petrol SI Engine – A path towards zero-emission H2 - ICEs".
Review Comments
The paper presents a simulation study on the utilization of oxy-combustion, direct water injection and Miller cycle Early Inlet Valve Closing (EIVC) in a Spark Ignition (SI) engine fueled by hydrogen. Simulation has taken place through commercially available Realis WAVE software and its accuracy was verified through experimental results published in literature. The subject matter of the paper is suitable for publication in the Energies Journal and also, the work, as far as I know, is original. The abstract is informative and the discussion adequately detailed.
I suggest the acceptance of the paper after Minor Revision.
My comments are as follows:
1. The use of English can be improved. I suggest editing by a native English speaker. Some paragraphs are not well written or are not understandable. Some examples are paragraphs in Lines 135-138, 255-257, 323-325, 445-451.
2. The authors provide a list of Abbreviations but some of the abbreviated terms are not explained. For example, CI (for Compressed Ignition) is not explained anywhere. Also, I believe that despite the addition of the Abbreviation list, the terms must be explained in the text when they are introduced for first time. This will improve the readability of the manuscript.
3. Lines 88, 92, 134, 144, 147, 163, 166 should not begin with a capital letter and should be appropriately aligned in the left margin of the manuscript.
4. The word “increasement” is rarely used in English. I suggest that the authors will correct it with other appropriate words such as “increment”, “growth” etc.
5. Line 31. Correct the phrase “…attracted huge amounts of engineer’s and scientists’ attentions” with something simpler and less exaggerated.
6. Lines 37-42. The authors confuse the reader when they speak about the utilization of carburators and gasoline injection. Please describe better the difference of these systems and when they are employed.
7. Equation (1) mentions an enthalpy change of -44.27 kJ/g but the text which follows mention an enthalpy change -47.87 kJ/g. Which is the correct amount?
8. Don’t write the units of numbers in italics. Correct in the entire manuscript.
9. Line 103. I suggest to correct the word “keeps” by “remains”.
10. The description of the Miller Cycle in Section 2.2. needs improvement. In Lines 101-107 please mention at what point of Figure 1 the inlet valve opens and closes (point 1a?) and how this is accomplished technically (special valve mechanism?). Also, describe better what do you mean by “blow back” effect and why it increases engine efficiency.
11. Line 118. Erase the word “structure”.
12. Line 121. A reference number is required after mentioning the work of Knaus et. al. Also, this work is not listed in the References.
13. Line 144. Change “length” by “diameter”.
14. Symbols in equation are different by the same symbols in the text. For example, in Line 144 symbols D, P and T must be corrected to be identical with those in Equation (5). Make the same correction in the entire manuscript.
15. Line 145. Explain the role and the assumed value for Cenht.
16. What are the reference temperature and reference pressure mentioned in line 147?
17.Which are the heat transfer coefficients assumed equal to 1? Lines 150-151 are not understood and can be misleading.
18. Line 166. Better define the angles theta_0 and theta_i in terms of CAD.
19.Figure 5a explains the EIVC scenarios examined in the study but one sees that both inlet valve closing timing and inlet valve lifting are changed simultaneously. Why did both parameters change simultaneously and upon what criretia? The effect of EIVC does not change when the valve lifting change at the same time? How one can isolate the two effects on the engine performance in such a way? Is the change of lifting inevitable when the valve timing changes? If so, why? Please explain these issues appropriately.
20. The symbol of hour in the SI system is “h” and not “hr”. Please correct appropriately in the entire manuscript.
21. Line 210. I believe that you have to correct into “….data exhibit downward trends at higher speeds”.
22. Place spaces before parentheses in Lines 272 and 278.
23. Lines 277-280. Which are these temperatures during the exhaust stroke? Are they average values? Please explain.
24. Hydrogen is known to have much higher flame velocity than gasoline. How does this affects the engine performance? For example does it have an impact on temperature or pressure increase rate? Why this is not observed in Figures 10a and 10b?
25. Line 309. Please rewrite the sentence to become understandable.
26. Line 348. Correct into “….temperatures are all above…”.
27.Line 355. Correct into “…charges and, thus, the cylinder…”
28. Please define the term “extent of early intake valve closure”. How is mathematically defined as a percentage value? Also, is there any correlation between this and the expansion ratio?
29. Line 378. Change “reduction” by “closure”.
30. Line 405. Correct as “….increases by 35.86%....” or appropriately.
31. Line 419. Correct the word “except”.
32. Line 423. Correct the word “model”.
33. Line 427. Correct as “At the rotational ….”.
34. Line 431. Correct into “….torque produced…”.
35. Line 437. Correct into “…8500 rpm.”.
36. The presentation and discussion of the Conclusions in Section 4 must be improved. Please make a better presentation of the results with clear and simple sentences. The presentation through bullet points and then through many “:” does not help the reader. Improve use of English.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsPlease explain the acronyms at their first appearance (line 36 for example)
Please introduce figures in the text before the figures itself (figs. 1, 3)
Please correct the references in line 121
Please explain the user defined variables of formula nr.3
The error of table/figure 6 and 7 is very very high the model should be calibrated on this brake power at least from 100% to 50% of the rpm. Here the error is higher at high rpm
Please correct: paragraph 3.1.4 have the title but not the test
Graphs of Figure 15 are not clear at all...the lines are similar to each other, this create confusing
The main dimensions of the baseline engine are not declared
The engine model construction should be better explained and detect
The calibration is poor
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
Comments and Suggestions for AuthorsAccept
