EGR and Emulsified Fuel Combination Effects on the Combustion, Performance, and NOx Emissions in Marine Diesel Engines

Round 1

Reviewer 1 Report

In this paper, the authors study the effect of the EGR, WFE, and their combinations on diesel combustion using an RCEM. The organization and composition of the manuscript are good. And the subject of the manuscript falls within the scope of this journal. However, there are some changes and improvements that need to be addressed before it can be accepted.

 

(1) Right, introducing the EGR and water in the cylinder are beneficial to reduce combustion temperature and the thermal NOx emissions. However, EGR and water techniques also have some disadvantages, such as low combustion rate and flame propagation. In addition, the combustion process and emissions formation and oxidation of the internal combustion engine are also affected by the spatial and temporal temperature history in the cylinder, boundary conditions, and engine operating conditions. Thus, the Introduction of this manuscript is insufficient. More related papers should be presented in the revised manuscript, which also enrich the analysis as well as the introduction section by letting the readers aware of the related progress (such as International Journal of Hydrogen Energy. 2020;45:17935-52; Energy Conversion and Management. 2019;195:1319-33).

(2) GT-Power is a powerful software. However, it needs a lot of experimental input data and boundary conditions, such as designing parameters, controlling parameters and operating parameters. For instance, how was data for cylinder head flow, swirl or tumble coefficient measured? In addition, which combustion model was used in this paper? More information should be listed in the manuscript. These works could help you validated the one dimensional GT-Power model and explain the validation process (Fuel. 2021;297:120762)

(3) Generally, the in-cylinder pressure and heat release rate are the crucial parameters to validate the simulation. It is chiefly because the in-cylinder temperature, heat transfer, piston movement and its conversion output power and emissions formation and oxidation are heavily relied on the in-cylinder pressure and heat release rate. Thus, why the authors did not present the in-cylinder pressure calibration in figure 10?

(4) Did the authors conduct the grid independent analysis when calibrated the KIVA-3V model?

(5) It is well known that, oxygen concentration, combustion temperature and the residence time of the reaction play decisive roles in the formation of NOx emissions. In addition, the formation of the CO emission is due to incomplete combustion caused by low cylinder temperature and low oxygen concentration, which slow the local oxidation reactions. Furthermore, the HC emissions are mainly attributed to several reasons as following. First, the unburned mixture in the cylinder escapes into the exhaust port during the gas exchange due to valve overlap. Second, the unburned mixture is compressed into the crevices in the combustion chamber, released during the exhaust valves opening and formed the HC emissions. Third, the unburned mixture is absorbed into the lubricating oil used for lubricating the piston and piston rings, and then released during the expansion stroke, particularly at the cold start conditions. Crevices in the combustion chamber play dominant role in the formation of HC emissions. Therefore, more fundamental explanations should be discussed in the revised paper.

 

(6) Besides, I would like to kindly suggest a revision with regard to the expression in English language: again, even if understandable, this good work would benefit from a little more clarity in some sentences.

Author Response

The authors wish to thank the reviewer for his insightful comments, which have substantially improved our manuscript. The response is included in the PDF file.

Author Response File: Author Response.pdf

Reviewer 2 Report

The effects of co-utilization of EGR and WFE on combustion and NOx emissions were studied on account of this the study is interesting and presents significant results. Some issues are addressed  below:

Issue 1. EGR has three main effects on reducing NOX emissions: Thermal effect, dilution effect, and chemical effect. However, the authors mentioned only the dilution effect in the introduction section. It is recommended to explain the other effects briefly.

Issue 2. Page 2 line 60 Authors wrote that "unless it can increase the possibility of nocking,"... Did the writers mean to write the word "knocking"?

Issue 3. "RHEODOL SP-L 10" is the product name of the used surfactant. It is more meaningful to use its chemical name (Sorbitan monolaurate). Additionally, the preparation steps for water in fuel emulsion can be presented, which would make it easier for new researchers in this area to form emulsion fuel.

Issue 4. The word "RCEM" is not given in the abbreviations section. or spell out the full term at its first mention, indicate its abbreviation in parenthesis, and use the abbreviation from then on.

Issue 5. The graphs in Figure 10 are not presented. Only the Figure caption is given.

 

Issue 6. The possible reasons for the increase in IMEP in the case of 18%O2 +WFE 40+increased injection pressure should be explained. As stated by the authors it was the only case that provided the NO reduction and the increased IMEP simultaneously. Therefore, it needs further interpretation.

Author Response

The authors wish to thank the reviewer for his insightful comments, which have substantially improved our manuscript. The response is included in the PDF file.

Author Response File: Author Response.pdf