Experimental Analysis of Water Pressure and Temperature Influence on Atomization and Evolution of a Port Water Injection Spray

Round 1

Reviewer 1 Report

1. The current study investigates the influence of water pressure and temperature on the atomization of port water injection spray used in cleaning applications.
2. The abstract must be modified and shortened, it cannot be accepted in its current state, in lines from 9-25 is just generic introduction which is more suited for introduction, please be concise and reduce this to several lines only. Then Please consider reviewing the abstract and highlight the novelty, major findings and conclusions.
3. What is GDI? Please mention the meaning of acronyms first time they appear in the manuscript
4. Introduction is not sufficient and must be expanded, please provide more critical literature review rather than generic one about spray and atomization systems, please report on past studies in more details and mention what they did, what were their main findings and what does the current study brings in terms of new knowledge and difference to the field.
5. After line 76 please answer the following question: What is the research gap did you find from the previous researchers in your field? Mention it properly. It will improve the strength of the article.
6. Please enlarge figure 1 it is very difficult to read any of the details in the description of the experimental setup
7. Please change the name of section 3 to results and discussion, I have never seen any papers use the word comments before
8. I don’t think the temperature have any significant effect on the injected mass. The effect is minor and can not be considered as significant or what the authors call evident. Perhaps if you want to point out this mention what is the difference in % terms because from looking at the two figures it is not showing this. For example, the mean injected quantity at 55 and 20 C is less than 3-4%!
9. Line 162-163 I don’t think there is any effect from temperature please consider checking this paragraph. It seems to me that in Figure 2 the pressure is the main factor affecting the mass flow
10. Figure 3 is not clear, there are four coloured lines but legends are only three, is there something missing there?
11. It is difficult to read the y axis of figure 4 a please fix this issue
12. Why the authors did not consider using design of experiments to provide a simple illustration of the influential parameters on the injection quantity. It appears that the combination of ET and temperature does make a difference on the injection quantity but the authors did not explain why? Could this be due to increased at higher ET?
13. Line 219 please avoid using unnecessary wording in your sentence such as “As expected and evidenced in Figure 7,” there is no need to stress out a point many times in one sentence
14. My question again in Figure 7 is this difference significant? Please try to describe it in terms of % it can better give the readers an idea of the influence of pressure
15. Line 286 “the atomization quality improvement was anyway not as” please rephrase this sentence
16. Moderate English changes required all over the manuscript
17. Please make sure that all the figures styles are consistent with each other, the later ones have different formatting style than the previous ones
18. The results are merely described and is limited to comparing the experimental observation. The authors are encouraged to include more discussion and critically discuss the observations from this investigation with existing literature.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The paper presents the impact of water injection into the engine intake system on its emission and operating parameters. The work presented for review is interesting. However, the authors did not avoid a number of mistakes.

Comments:

1. Why is such a careful water injection analysis important for indirect injection? The temperature in the engine cylinder is high enough for the water to evaporate quite early. Were these results used to optimize the engine?
2. On what basis did the authors choose such a range of injected water?
3. How was the dose of a single shot measured? With what accuracy was it determined?
4. Energizing time [ms] (in Fig. 2) and Time [ms] it is this same time? If so, the units should be standardized. In Abbreviations is: ET [ms].
5. In Figures 5 and 6 it would be good to add a length scale to determine the extent of the stream.
6. In Figure 8 is: Time from ET. Is it time from the start of injection? It is unclear here.
7. In Figure 11 is: Time after ET Start [ms]. It is time after closing the injector?

 

Editorial:

1. Figure 1 is hard to read.
2. Graph 4a is poorly formatted and difficult to read,
3. What does unit mean: for example 15 bar,g?
4. In Fig. 3 are 4 lines but only 3 in the legend description. It is similar in Fig. 2b.
5. In Fig/ 6d is Ta=-11=oC. Please correct it accordingly.
6. The captions under the charts are not very precise.You use the letters a-d to mark the graphs, but the caption is not there. This makes it very difficult to read the charts, the reviewer must guess what is on the charts for which parameters.

Summarizing, please indicate which water droplet distribution is optimal? What range, what the speed of the drop, etc. are the best for engine.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

In the current paper, an investigation of spray characteristics from a indirect water injection system intended for spark-ignition engines is performed. The paper is well structured, the methodology used is consistent with the research objectives and the conclusions can be of interest for other researchers working on the field. However, a few suggestions for improvement are provided below:

1) Figure 1 is hardly readable. I would arrange both setups vertically instead of horizontally, in order to use the full page width, making the labels' font larger.

2) Why did the authors consider only room conditions (1 bar 25ºC) for the discharge? Considering that, as they well explain in their introduction, knocking trend would be higher at high load and low speed conditions, discharge pressures around 2-2.5 bar and temperatures in the range of 40-45ºC would be more relevant. If the it is due to limitations in the experimental arrangement, it should be at least discussed.

3) Given the fact that the test design for spray visualization is a full factorial, expressing it as a table (Table 3) may not be necessary. It would suffice to express in the main text the values of injection pressure and water temperature considered. Instead, for PDPA I would maintain Table 5 to provide in a simple way the conditions that were skipped.

4) Please provide the details of the injector command signal supplied. Is it a simple 5V voltage square signal with a certain duration, and the current seen in Figure 3 would be the result in the coil? Additionally, the legend in Figure 3 is not complete. Please rearrange it.

5) From Figure 6 it would seem that the injector has 3 or 4 discharge holes. Please provide this information when describing the injector in section 2. Also, looking at the spray structure, characterized by very disperse droplets far from the nozzle tip, it would seem that the spray penetration can be very sensitive to the specific method used to determine it from the images (background correction, intensity threshold, maximum distance on axis vs. maximum distance overall, etc). Have the authors performed a sensitivity on this?

6) Looking at Figure 7, the spray penetration results from 5 and 7 bar injection pressure seem overlapped for the lower temperature levels (20 and 55 ºC), while expected trend appears at higher temperatures. I wonder if this change of behavior can be affected by a transition on turbulence regime. Can the authors provide an estimation of Reynolds number at the nozzle exit based on the holes diameter and the mass flow?

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

All questions answered and the paper can be accepted.