An Experimental Study on the Flash Boiling Characteristics of Liquid Ammonia Spray in a Constant Volume Chamber under High Injection Pressure
, Jie Wu 1, Lei Wang 1, Hua Lou 1, Songfeng Li 1, Lvmeng Huang 2 and Zhanming Chen 1,2,*
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsIn the present work, the authors conducted an experimental study to examine the ambient and injection pressures on the jet evolution of liquid ammonia. The Schlieren method was employed to detect the liquid and vapor boundaries. The liquid and vapor penetration lengths as well as the corresponding projected area were measured. Overall, the topic of this work is interesting, and the findings are reasonably discussed. However, to be published as a journal paper, the following comments should be addressed:
Major points:
1. Generally, the English is reasonably good, but there are many small typos that affect the paper quality. For example, in the title, it should be ‘An experimental study on …’. In the abstract, ‘Moreover, ambient pressure …’ and ‘With increasing ambient pressure’. There are many typos like that. Please double-check during the revision. The authors may install ‘Grammarly’ for that purpose.
2. From the Introduction, the reader may get the impression flash boiling is not good. Should we take advantage of flash boiling, which might benefit from faster evaporation? The authors may consider this point and add relative discussions.
3. More details related to the experimental setup should be provided. For example, how did the authors control the CVC temperature? There is no thermocouple from Figure 1. Most importantly, how did the authors detect liquid and vapor phases (penetration and area) using the Schlieren method only? Are there any experimental uncertainties? How was the ammonia temperature controlled at 320 K? And the dimension of the CVC as well as the optical window?
4. Is Rp of 0.32 good enough as the transition flash boiling point? Considering it is very close to the flare boiling point (0.3), maybe it is better to use 0.5 or 0.6? As we can see from the measured results, the transition flash boiling point (0.32) showed a similar trend to the flare boiling point (0.1). Please comment on this.
5. The authors may consider using more literature references that conducted similar research work to support their findings. For example, the trend of penetration lengths with the function of ambient and injection pressures.
6. ‘spray resistance phenomenon’ is very interesting. Please add more supporting references for the discussions of this.
Minor points (mostly grammatical):
1. In the abstract, it is unusual to use ‘penetration distance’. ‘late spray’ can be ‘late stage of the injection’. Please have an explanation or change the word for it. In addition, ‘nozzle hole’ is recommended instead of ‘spray hole’. ‘Obstruction of ambient gas’ is not a good phrase, why not use ‘restriction’ instead?
2. Line 44, is the LHV of NG 47.2 MJ/kg? Shouldn't it be about 50 MJ/kg? Line 47, please use ‘these approaches such as’. Line 65, ‘However’ is frequently used. Maybe the authors can use ‘Note that’. Line 74, what is ‘current spark ignition GDI’? Line 75, ‘geometry’ should be ‘jet structure’?
3. Line 87, ‘there is no need to increase the injection pressure when gaseous ammonia was used due to the low boiling point’. Is this true? What is the normal PFI injection pressure for ammonia?
4. Line 147. 1.87 MPa could not be seen from Table 3. Please double-check. Typo. Line 159, ‘when the ambient’. Line 216, should it be ‘Two different injection pressures’? Line 262, ‘accelerated’ should be ‘accelerate’. Line 275, ‘elevating’ should be elevation’. Line 278, ‘regarded to’ should be ‘attributed to’. Line 281, what is ‘spray penetration gap’?
5. ‘Figure 5’. Why are the initial penetrations at 80 MPa not zero? What is the resolution of the camera response time? For example, what is the frequency between two consecutive images?
6. Again. ‘liquid penetration distance’ is not a good phrase. Why not use ‘liquid penetration length’ as in the literature? Line 241, ‘penetration of the spray gas region’ should be ‘vapor penetration length’.
7. Line 328. ‘at the state of cold under other conditions’ should be ‘at cold conditions’. By the way, is it at room temperature? Line 372. ‘as Pa’ increased ‘as the ambient pressure increased’.
8. A minor suggestion. In Figures 11 and 12, maybe the penetration areas of the liquid region can be removed.
9. In the introduction, the authors may consider citing two recent works on ammonia spray and combustion, ‘J. Clean. Prod. 436 (2024) 140622’ and ‘SAE Technical Paper 2022-01-1078’. And regarding the discussion of cavitation, the authors may consider taking a reference of ‘Int. J. Engine Res. 25 (2023) 613-630’.
Comments on the Quality of English LanguageThe English is generally fine. But there are several grammatical typos that must be rectified.
Author Response
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Author Response File: 
Author Response.docx
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors presented an experimental study the flash boiling characteristics of liquid ammonia spray in a constant volume chamber under high injection pressure. The paper has good scientific soundness and can be accepted after minor revisions:
The main quantitative results are to be mentioned in the abstract
The novelty of the paper is to be clearly stated
An actual photo of the experimental setup is to be added
The data acquisition system and measurement techniques are to be described in details
An experimental uncertainty study is to be performed
Why is the time limited to 0.4 seconds in some experiments?
Author Response
The point-by-point response can be found as the upload file
Author Response File: Author Response.docx
Reviewer 3 Report
Comments and Suggestions for AuthorsThe authors have investigated experimentally the spray characteristics of liquid ammonia under varying ambient pressures and temperatures, spanning a wide range of superheat degrees. The work is presented in a well-structured manner and easy to understand. Following are few suggestions which will help improve the overall quality of the paper.
1. Literature review is not comprehensive with only 20 citations mostly from years 2021/ 2022/ 2023. This can be improved by highlighting the previous work done in at least past decade and improvement in the technology.
2. Only the data for the development of transition flash boiling spray over time, obtained from experiment, is presented for various conditions. However, a comparison of current work results with literature or theory is absolutely missing. This is very important for a reader as readers are not only interested in current study outcomes but want to see the comparison, either with theory or previously published work.
3. Can you explain why in the experiment, the ambient temperature in the tank was preheated to 500 K, and why the temperature of liquid ammonia fuel was fixed to 320 K? Any specific reason?
4. Figure 2: The font size of the "Lables and Axes title" is too small to read. Please increase the font size used in Figure 2.
5. In acknowledging section please replace "im-prove" to "improve".
Comments on the Quality of English LanguageThe quality of English in the manuscript is good.
Author Response
The point-by-point response can be found as the upload file
Author Response File: Author Response.docx
Reviewer 4 Report
Comments and Suggestions for AuthorsThe paper entitled “An experimental study the flash boiling characteristics of liquid ammonia spray in a constant volume chamber under high injection pressure” deals with studying flash boiling characteristics of liquid ammonia spray under high injection pressure regarding using of liquid ammonia as an alternative fuel for internal combustion engines.
The topic is hot, the high energy content of ammonia attracts attention to use it in internal combustion engines as fuel or co-fuel. Because ammonia is a polar low-boiling point liquid, its flash boiling under spraying under the circumstances of engine conditions is an important phenomenon, thus studying this topic is useful, and collecting data about it has high importance The literature contains data about liquid ammonia flash boiling below 30 MPa injection pressure, but the studies over higher injection pressures than 30 MPa give new pieces of information.
The selected test methods and the evaluation of the results are adequate and clear. The paper is written fluently. The target is clear, and the descriptions of the test methods and the experimental setup are correct. The gas-liquid penetration measuring requests a large number of points, which were done by authors to show the tendencies of the measured data in the function of a wide scale of variables, which gives a solid base for conclusions.
The discussion part is as short as a conclusion. Perhaps it had better call Chapter 3 “Results and Discussion” and insert the discussion part information into this chapter, and Chapter 4 could be shortened and called to be “Conclusion”.
Based on a large number of experimental data, clear targets, well-built experiments, and correct evaluations, I can suggest publishing the paper after a minor revision mentioned above.
Author Response
The point-by-point response can be found as the upload file
Author Response File: Author Response.docx
Round 2
Reviewer 3 Report
Comments and Suggestions for AuthorsAuthors have responded well to the questions raised in first review; however, I still suggest increasing the font size of the axes title and legend in FIGURE 2.
