An Investigation of the Influence of Gas Injection Rate Shape on High-Pressure Direct-Injection Natural Gas Marine Engines

Round 1

Reviewer 1 Report

1.       Line 34 – heave should be corrected (heavy).

2.       Line 83. The space after recently and before comma position to be removed.

3.       References no 32, 33 and 34 seems not to have been introduced in the text of the manuscript. Please introduce them.

4.       Line 96. I suggest the authors to briefly present the findings of the mentioned references [28,31, 35-41].

5.       I suggest statement in line 105 to be supported by relevant references [28-45] or to be connected with previous paragraph.

6.       In order to be more convenient to the reader, I suggest the table 1 reference (line 123) to be put in the manuscript, before the table itself (line 118).

7.       In order the references sequence to be more easily followed by the reader, I suggest table 2 (line 144) to be put before reference 57 mentioning in the text (line 141).

8.       I understand that in line 165, figure no (figure 4.) is wrong. I suppose the correct is figure 2, please change it. I suggest also figure 2 to be put before table 3 in the manuscript.

9.       Line 195 – A space before “Therefore”, must be possibly removed. The same before “Short” in line 208.

10.   In order to be more convenient for the reader I suggest Figure 5 (a) to (d)  to be presented in the same page or figure 5 (d) to be a separate figure.

11.   It would be interesting, the specifications of the natural gas and the diesel where used for the experiments to be presented in the manuscript. I suggest the authors to do so. These could also be discussed in correlation to references no 14 and 15.

Below references could also be considered for above discussion

Golimowski, W.; Krzaczek, P.; Marcinkowski, D.; Gracz, W.; Wałowski, G. Impact of Biogas and Waste Fats Methyl Esters on NO, NO2, CO, and PM Emission by Dual Fuel Diesel Engine. Sustainability 2019, 11, 1799.

Najafi, B.; Akbarian, E.; Lashkarpour, S. M.; Aghbashlo, M.; Ghaziaskar, H. S. and Tabatabaei, M.; Modeling of a dual fueled diesel engine operated by a novel fuel containing glycerol triacetate additive and biodiesel using artificial neural network tuned by genetic algorithm to reduce engine emissions. Energy (168) 2019, pp. 1128-1137.

Ashok, B. and Nanthagopal, K.; 15 - Eco friendly biofuels for CI engine applications, In Woodhead Publishing Series in Energy, Advances in Eco-Fuels for a Sustainable Environment, Eds: Kalam Azad. Woodhead Publishing 2019, pp. 407-440.

12.   There are some linguistic mistakes and language improvement is possible. I suggest the authors to review English language once again.

Author Response

Respond to reviewer 1

The authors would like to express our sincere thanks to the reviewer for the valuable suggestions. We have checked the whole manuscript according to the suggestions, and the detailed responses are as follows:

1.         Line 34 – heave should be corrected (heavy).

R: Thank you, the word has been corrected.

 

2.         Line 83. The space after recently and before comma position to be removed.

R: Thank you, the space has been removed.

 

3.         References no 32, 33 and 34 seems not to have been introduced in the text of the manuscript. Please introduce them.

R: Thank you, I apologize that the descriptions cited references NO 32, 33 and 34 were removed in previous manuscript because the descriptions are less relevant to the content in present study. The references NO 32, 33 and 34 have been removed in the revised manuscript and the numbers of references have been corrected.

 

4.         Line 96. I suggest the authors to briefly present the findings of the mentioned references [28,31, 35-41].

R: Thank you, the findings of the mentioned references have been described in the revised manuscript.

 

5.         I suggest statement in line 105 to be supported by relevant references [28-45] or to be connected with previous paragraph.

R: Thank you, the statement has been supported by references [29-41] in the revised manuscript.

 

6.         In order to be more convenient to the reader, I suggest the table 1 reference (line 123) to be put in the manuscript, before the table itself (line 118).

R: Thank you, the reference has been put before the table 1 in the updated manuscript.

 

7.         In order the references sequence to be more easily followed by the reader, I suggest table 2 (line 144) to be put before reference 57 mentioning in the text (line 141).

R: Thank you, a general description has been put before reference 55, and the references NO 45~54 is cited in this section.

 

8.         I understand that in line 165, figure no (figure 4.) is wrong. I suppose the correct is figure 2, please change it. I suggest also figure 2 to be put before table 3 in the manuscript.

R: Thank you, the Figure NO has been corrected, and the Fig. 2 has been put before table 3 in the revised manuscript.

 

9.         Line 195 – A space before “Therefore”, must be possibly removed. The same before “Short” in line 208.

R: Thank you, the two spaces have been removed.

 

10.     In order to be more convenient for the reader I suggest Figure 5 (a) to (d) to be presented in the same page or figure 5 (d) to be a separate figure.

R: Thank you. Figure 5 has been divided into Figure 5 and Figure 6.

 

11.     It would be interesting, the specifications of the natural gas and the diesel where used for the experiments to be presented in the manuscript. I suggest the authors to do so. These could also be discussed in correlation to references no 14 and 15.

Below references could also be considered for above discussion

Golimowski, W.; Krzaczek, P.; Marcinkowski, D.; Gracz, W.; Wałowski, G. Impact of Biogas and Waste Fats Methyl Esters on NO, NO2, CO, and PM Emission by Dual Fuel Diesel Engine. Sustainability 2019, 11, 1799.

Najafi, B.; Akbarian, E.; Lashkarpour, S. M.; Aghbashlo, M.; Ghaziaskar, H. S. and Tabatabaei, M.; Modeling of a dual fueled diesel engine operated by a novel fuel containing glycerol triacetate additive and biodiesel using artificial neural network tuned by genetic algorithm to reduce engine emissions. Energy (168) 2019, pp. 1128-1137.

Ashok, B. and Nanthagopal, K.; 15 - Eco friendly biofuels for CI engine applications, In Woodhead Publishing Series in Energy, Advances in Eco-Fuels for a Sustainable Environment, Eds: Kalam Azad. Woodhead Publishing 2019, pp. 407-440.

R: Thank you for your advice. The specifications of natural gas and diesel are described in the revised manuscript. And a brief discussion is conducted in correlation to the references you mentioned.

 

12.     There are some linguistic mistakes and language improvement is possible. I suggest the authors to review English language once again.

R: Thank you, English proof reading was conducted to further improve the writing.

Reviewer 2 Report

In this paper, the authors investigate the effect of natural gas injection rate shape on the performance of high-pressure directly-injected dual-fuel (diesel and natural gas) marine engines. They use the finite volume CFD model to compare the fuel consumption, and various emissions (NOx, soot, CH4, and CO+HC) for 5 different injection rate shapes and show that the wedge and trapezoid shape achieve a good balance between the fuel consumption and emissions.

I believe the manuscript has lots of merits, however, it is not very well presented.

- There are very few details on the numerical simulation model used for investigating the problem. In its current form, the document is composed of the introduction and the results. Although the authors have cited the sub-models used in the simulation in section 2.2, the general formulation should be included in the manuscript as well along with more detail on the system that is being investigated.

- Previous works such as “Effect of diesel pre-injection timing on combustion and emission characteristics of compression ignited natural gas engine”, etc., should be cited properly.

- Extensive editing of the language is required. Also, there are multiple typo and errors throughout the text that needs to be taken care of.

Author Response

Respond to reviewer 2

The authors would like to express our sincere thanks to the reviewer for the valuable suggestions. We have checked the whole manuscript according to the suggestions, and the detailed responses are as follows:

 

1.       There are very few details on the numerical simulation model used for investigating the problem. In its current form, the document is composed of the introduction and the results. Although the authors have cited the sub-models used in the simulation in section 2.2, the general formulation should be included in the manuscript as well along with more detail on the system that is being investigated.

R: Thank you. A general description of sub-model and system has been added in the revised manuscript.

 

2.       Previous works such as “Effect of diesel pre-injection timing on combustion and emission characteristics of compression ignited natural gas engine”, etc., should be cited properly.

R: Thank you for your advice. The reference has been properly cited in the updated manuscript.

 

3.       Extensive editing of the language is required. Also, there are multiple typo and errors throughout the text that needs to be taken care of.

R: Thank you, English proof reading was conducted to further improve the writing.

 

Reviewer 3 Report

The article deals with a numerical analysis on the effect of the fuel injection rate shape on the combustion parameters and emissions in high pressure direct injection reciprocating engines, using natural gas as fuel. The topic is of high relevance due to the increasing use of liquefied natural gas in marine applications, mainly for environmental concerns.

The work has been adequately introduced. The numerical model and the aim of the analysis have been illustrated with sufficient detail. A validation of the model has been carried out by comparing the numerical results obtained for a trapezoidal injection rate with experimental data availabel in the literarture. The analysis results have been adequately illustrated, although in some points need to be better clarified, as indicated below. The conclusion needs to be improved as herein suggested.

Page 5, Fig. 2: Is the comparison again for a trapezoidal injection rate with respect to experiment of ref 60 as for Fig 1? please clarify.

Tables 2 and 4. : in which axial position of the cylinder the slices are taken? Please justify why the position chosen is considered representative.

Page 11, from row 314 to 325. The discussion of the results relevant to CH4 emission is not very clear, since refers to Fig. 6 which is not indicated and comes after comments made on results shown in Fig. 7. Maybe a rearrangement of the contents should be helpful. No reference is given to support the statement of rows 324 and 325 about the flammability limit (no indication about the source of the experimental result).

The conclusion should be extended considering:

- what is the realistic possibility to change the injection rate shape with respect to the trapezoidal, which is the most close to a real one?

- as a consequence, how reliable can be considered the results obtained with different injection shapes without a proper comparison with experimental data?

 

Author Response

Respond to reviewer 3

The authors would like to express our sincere thanks to the reviewer for the valuable suggestions. We have checked the whole manuscript according to the suggestions, and the detailed responses are as follows:

 

1.       Page 5, Fig. 2: Is the comparison again for a trapezoidal injection rate with respect to experiment of ref 60 as for Fig 1? please clarify.

R: Thank you. Since the simulated engine is not the same engine as reference 60, the comparison for a trapezoidal rate with experimental data of ref 60 is unnecessary. The purpose of comparison of interaction between gas jet and diesel spray is to verify the accuracy of the sub-model used in the manuscript. Since the simulated results are in reasonable agreement with experimental data, the INFLOW boundary can be used to simulate the gas jet.

 

2.       Tables 2 and 4. in which axial position of the cylinder the slices are taken? Please justify why the position chosen is considered representative.

R: Thank you. Each slice in Table 4 and Table 5 is superimposed by four different slices. Since the natural gas injectors has four nozzles, and the four nozzles are in different axial position of the cylinder. A slice taken though the center of a nozzle can just display the equivalence ratio and temperature distributions evolved from this gas jet. To display the equivalence ratio and temperature distribution for all the gas jet, the four slices taken though the center of four different nozzle are selected.

 

3.       Page 11, from row 314 to 325. The discussion of the results relevant to CH4 emission is not very clear, since refers to Fig. 6 which is not indicated and comes after comments made on results shown in Fig. 7. Maybe a rearrangement of the contents should be helpful. No reference is given to support the statement of rows 324 and 325 about the flammability limit (no indication about the source of the experimental result).

R: Thank you for your advice. The discussion has been rearranged and reference 61 has been cited to support the flammability limit of methane in the revised manuscript.

 

4.       The conclusion should be extended considering:

- what is the realistic possibility to change the injection rate shape with respect to the trapezoidal, which is the most close to a real one?

R: Thank you. The rectangle and wedge shapes are close to square shape and ramp shape studied in reference [34]. The triangle shape is close to typical injection rate shape of Caterpillar HI90 diesel injector [SAE 2004-01-0530]. The slope shape is closed is close to the ramp shape studied in a single-cylinder engine [39].

 

5.       as a consequence, how reliable can be considered the results obtained with different injection shapes without a proper comparison with experimental data?

R: Thank you. Since the simulated model has been validated with experimental data, and the interaction between gas jet and diesel spray is also validated with experimental data. The model used in present study is reliable to predict the combustion and emission performance of the original engine.  Even if the initial and boundary conditions change, the predicted results are still reliable.

 

Reviewer 4 Report

In this article CFD model was used to study the effects of gas injection rate shape on the combustion characteristics and performance. In the introduction the novelty of the study is well explained. The results were also well discussed. I’d rather to see the model was validated by the experimental results from authors. Nevertheless, the still is acceptable for publish after correcting the following minor comments.

Line 34: correct “heave”

Line 37: “The emission of CO2 is a greenhouse gas and…” remove “the emission”

Line 105: change “include” to “including”

Fig. 1: Some explanation is needed how modeling data confirm experimental findings.

Line 78: change “select” to “selected”

Please make the conclusions shorter.

Author Response

Respond to reviewer 4

The authors would like to express our sincere thanks to the reviewer for the valuable suggestions. We have checked the whole manuscript according to the suggestions, and the detailed responses are as follows:

 

1.       Line 34: correct “heave”

R: Thank you, the error has been corrected in the updated manuscript.

 

2.       Line 37: “The emission of CO2 is a greenhouse gas and…” remove “the emission”

R: Thank you, “The emission of” has been removed.

 

3.       Line 105: change “include” to “including”

R: Thank you, “include” has been changed to “including”

 

4.       Fig. 1: Some explanation is needed how modeling data confirm experimental findings.

R: Thank you, an explanation is added in the revised manuscript.

 

5.       Line 78: change “select” to “selected”

R: Thank you, the word has been corrected.

 

6.       Please make the conclusions shorter.

R: The conclusions have been shortened.

 

Round 2

Reviewer 2 Report

After carefully reading through your answers and modifications in the manuscript, I like to recommend the publication of this paper in its present form.