Ensuring Operational Performance and Environmental Sustainability of Marine Diesel Engines through the Use of Biodiesel Fuel

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this article, the authors have investigated the issues related to ensuring the operational performance and environmental sustainability of marine diesel engines using biodiesel fuel. This research was conducted on 5S60ME-C8 MAN-B&W marine diesel engines and 6DL-16 Daihatsu Diesel marine diesel engines operating using RMG380 petroleum fuel and B10 and B30 biodiesel fuels. The authors reported that the use of B10 and B30 biofuels B30 reduces the concentration of nitrogen oxides in exhaust gases by 14.71-25.13%, but at the same time increases the specific effective fuel consumption by 6.01-1.55%. According to the title of the article “Ensuring operational performance and environmental sustainability of marine diesel engines through the use of biodiesel fuel” It was expected that all performance parameters and environmental pollutants of diesel fuel would be investigated. In this article, the focus has been on the reduction of NO_X, and the result obtained also has doubts that the authors should correctly state the reason for the reduction by carefully examining the other references.

 

1- Considering that the title of the article is about the use of biodiesel in the marine diesel engine, in the section of literature review and introduction, more things should be said about biodiesel fuel. In this section, the authors have given explanations about other alternative fuels such as alcohols and hydrogen, but the explanations provided about biodiesel do not seem sufficient. Please see the reference below for more information. https://doi.org/10.3390/su14063284

2- Only NOx have been investigated in the article. One of the most important pollutants of diesel engine is particulate matter. Was there no need to check these pollutants? https://doi.org/10.1080/17597269.2024.2330188

3-Figure 5-a should be revised. Numbering 1, 2 and 3 is done in the figure, if only DF and 1 and 2 are explained in the description of the caption.

4-Very important aspects of engine performance such as power and torque are ignored in this article. What effect has the use of fuel blends had on these parameters?

5-The first sentence of the discussion and conclusion sections are the same:

“One of the options for ensuring the environmental performance of marine diesel engines (primarily nitrogen oxide emissions NO_X) is the use of biofuels”

“One of the ways to ensure environmental efficiency and expand the range of environmental sustainability of marine diesel engines is the use of biofuels”

6- According to the results intended by the authors, it is better to change the title

Author Response

1- Considering that the title of the article is about the use of biodiesel in the marine diesel engine, in the section of literature review and introduction, more things should be said about biodiesel fuel. In this section, the authors have given explanations about other alternative fuels such as alcohols and hydrogen, but the explanations provided about biodiesel do not seem sufficient. Please see the reference below for more information. https://doi.org/10.3390/su14063284

 

We have added information to the literature review and introduction sections.

We have highlighted this information as

¹¹Vegetable oils as motor fuels can be used both in pure form and in a mixture with diesel and other petroleum fuels, as well as with gas condensates, alcohols, ethers and other alternative fuels. The source of vegetable oils are oil crops, the seeds or fruits of which contain vegetable fats. Oil plants include more than 150 species of plants from which vegetable oils are produced. Depending on the climatic conditions and the availability of cultivation, raw materials for the production of biodiesel can be various vegetable oils - from olive oil to animal fat.

About 87.4% of the world production of vegetable oils is palm, soybean, rapeseed and sunflower oils, the remaining 12.6% is peanut, cottonseed, olive, coconut and palm kernel. Undoubtedly, most of this volume is used in the food industry. However, part of the oil is used as raw material for biofuel production. Rapeseed oil ranks third in terms of production in the world after palm and soybean oil. At the same time, rapeseed oil is the most actively used for the production of biodiesel fuel. Different vegetable oils contain different amounts of fatty acids, which leads to certain differences in their characteristics. All vegetable fuels have similar basic characteristics to each other - density, flash point, lower calorific value. During combustion, they emit approximately 10...12% less heat than petroleum-based diesel fuel. There are no standards for the calorific value of fuel from oil, but a higher calorific value of fuel is an important property used in determining its quality.

The American society of testing and materials (ASTM) defines the cetane number as the main quality characteristic of fuel based on vegetable oils. The ASTM D6751 specification specifies a minimum cetane number of 47 for vegetable fuels.

All vegetable oil-based fuels made from the most commonly used feedstock exceed this value. A distinctive feature of oil fuels is the minimum level of sulfur content. This allows their use in special ecological areas – SECAs).

The ecological efficiency of biofuel use is also characterized by a lower amount of carbon dioxide produced during its combustion. When burned, traditional fuels produce a large amount of carbon dioxide, which is considered a greenhouse gas and the reason for keeping the sun's heat on the planet. Burning coal and oil raises the temperature and causes global warming. The use of biofuel reduces the impact of greenhouse gases on the environment.

Various scientific studies contain conflicting data regarding the amount of nitrogen oxides NO_X emissions when using biodiesel fuel. This discrepancy is related to the variability of the experiment, the type of petroleum fuel, as well as the conditions of the experiment (biofuel concentration in the fuel mixture with petroleum-derived fuel, diesel engine operating modes, features and characteristics of its cooling and exhaust systems).

 

We have also added the reference you recommended.

69. Shadidi, B.; Najafi, G.; Zolfigol, M.A. A Review of the Existing Potentials in Biodiesel Production in Iran. Sustainability. 2022, 14, 3284. https://doi.org/10.3390/su14063284.

 

2- Only NOx have been investigated in the article. One of the most important pollutants of diesel engine is particulate matter. Was there no need to check these pollutants? https://doi.org/10.1080/17597269.2024.2330188

 

We have added the following information.

¹²In addition to oxides of sulfur SO_X and nitrogen NO_X, the exhaust gases of marine diesel engines also contain other harmful components. Primarily, these are carbon dioxide CO, particulate matter PM, black carbon C. However, international standards for limiting such emissions have not been approved at the moment. The emission of carbon dioxide CO is regulated by the requirements of the Kyoto Protocol; monitoring of particulate matter PM emissions is more relevant for road transport, which operates in urban regions and affects the atmosphere significantly; monitoring of black carbon C emissions is especially relevant for the northern latitudes of Europe and the Polar regions.

 

We have also added the reference you recommended.

67. Najafi, G.; Shadidi, B.; Mamat, R.; Safieddin Ardebili, S. M.; Hazrati, S.; Ebadi, M. T.; Ghazali, M. F. Multi-objective optimization of the performance and emissions characteris,tics of a CI engine powered by Pyrus glabra biodiesel as a novel feedstock using response surface method. Biofuels. 2024. 1–10. https://doi.org/10.1080/17597269.2024.2330188.

 

3-Figure 5-a should be revised. Numbering 1, 2 and 3 is done in the figure, if only DF and 1 and 2 are explained in the description of the caption.

 

We revised Figure 4-a. (As we understand, your comment refers to Figure 4a).

 

4-Very important aspects of engine performance such as power and torque are ignored in this article. What effect has the use of fuel blends had on these parameters?

 

We have added the following information.

¹⁴Fuels of biological origin are characterized by a lower calorific value compared to fuels of petroleum origin. At the same time, the amount of energy released during combustion of biofuel in the diesel cylinder decreases. This is the reason for the decrease in torque and power of the diesel when it operates only on biofuel. That is why biodiesel fuel is not used in its pure form (only as FAME fuel), in addition, the composition of biodiesel fuel in its mixture with fuel of petroleum origin does not exceed 30% (which corresponds to biodiesel fuel B30). In this case, maintaining the required torque (and consequently the power of the diesel engine) is ensured by maintaining the required crankshaft rotational frequency. This necessitates increasing the cycle fuel supply when using biodiesel fuel.

 

5-The first sentence of the discussion and conclusion sections are the same:

“One of the options for ensuring the environmental performance of marine diesel engines (primarily nitrogen oxide emissions NO_X) is the use of biofuels”

“One of the ways to ensure environmental efficiency and expand the range of environmental sustainability of marine diesel engines is the use of biofuels”

 

We have replaced the first sentence of the discussion section with the following text.

¹⁵The operation of marine diesel engines is inseparably linked not only to ensuring their required power but also to maintaining the environmental performance of their operation. In this regard, the main parameters regulated by the requirements of Annex VI of MARPOL are the sulfur content in the fuel and the emission of nitrogen oxides. Ensuring the environmental sustainability of marine diesel engines can be achieved by using fuel blends that include biodiesel. The combustion of biodiesel results in a reduction of nitrogen oxide concentrations in the exhaust gases.

 

6- According to the results intended by the authors, it is better to change the title

 

We believe that the results of the article reflect the title of the article.

The results confirm that the use of biodiesel fuels affects the energy, economic, and environmental performance of diesel engines. In this case, two different fuels were selected as biodiesel: B10 (with a biodiesel content of 10%) and B30 (with a biodiesel content of 30%); and two different engines were used: the two-stroke 5S60ME-C8 MAN-B&W and the four-stroke 6DL-16 Daihatsu Diesel. Additionally, optimal injection timing angles for biodiesel fuel were determined, at which the best values for such performance indicators of marine diesel engines as maximum combustion pressure, exhaust gas temperature, specific fuel consumption, and nitrogen oxide concentration in exhaust gases are achieved.

Marine diesels (like other thermal engines) have other important operational indicators as well. However, it is not possible to investigate all these indicators within the scope of a single study.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This work stands out for its focused investigation on using B10 and B30 biodiesel blends in marine diesel engines, a topic less explored than similar research on road and railway engines. It uniquely evaluates two- and four-stroke engines, providing comprehensive insights into biodiesel's impact on fuel consumption, emissions, and optimal injection timing. The study's dual emphasis on environmental and economic performance, alongside practical operational data, sets it apart from other literature, making a significant contribution to sustainable marine engineering.

This work is good but needs more important points to be addressed before its acceptance. Hence, I suggest a minor revision.

1. Could the authors elaborate on the rationale for selecting various load levels (e.g., 65%, 75%, 85%, 95%) for evaluating the main engine?

2. How do these loads align with the actual operating circumstances experienced by marine diesel engines in the real world?

3. Testing is done on a Bulk Carrier vessel. How representative is the vessel in question of the maritime fleet? Could vessel or engine designs drastically affect results?

4. The paper discusses the use of B10 and B30 biodiesel blends. Were any other blends (e.g., B20) considered? Explain the reason

 

Comments on the Quality of English Language

The quality of the English language used in the paper is good.

Author Response

1. Could the authors elaborate on the rationale for selecting various load levels (e.g., 65%, 75%, 85%, 95%) for evaluating the main engine?

We have added the following information.

²¹The choice of the main engine load levels was justified by the following. According to the requirements of diesel operation, its continuous operating power should not exceed 95% of the rated power. Reducing the main engine power below 65% reduces the ship's speed significantly. That is why the research was conducted in the range of 65–95% with an interval of 10%.

 

²¹The choice of the auxiliary engine load levels was justified by the following.According to the requirements for diesel operation, their continuous operating power should not exceed 80% of the rated power.Reducing the power of auxiliary diesel engines below 50% significantly increases the specific effective fuel consumption and temperature stress of the cylinder group parts.That is why the research was conducted in the range of 50–80% with an interval of 10%.

 

2. How do these loads align with the actual operating circumstances experienced by marine diesel engines in the real world?

We have added the following information.

²²At the same time, this load range met the requirements of the charterer and the shipping company. In addition, this range is the most common of all operating modes for most diesel engines used on seagoing vessels as main engines.

²²At the same time, this range of loads provided energy to all ship consumers (navigation equipment, deck mechanisms, ship systems, engine room mechanisms). In addition, this range is the most common of all operating modes for most diesel engines that are used on sea vessels as auxiliary ones.

 

3. Testing is done on a Bulk Carrier vessel. How representative is the vessel in question of the maritime fleet? Could vessel or engine designs drastically affect results?

The tests were conducted on the vessel where one of the authors of the article worked as a second engineer. Another author of the article is a representative of the company that provides technical management of the vessel. This determined the choice of the vessel. Similar tests can be conducted on any vessel whose main and auxiliary engines can operate using biodiesel fuel. The design of the vessel and the engine do not fundamentally affect the results. We conducted research for two types of diesel engines: a two-stroke, which was used as the main engine, and four-stroke ones, which were used as auxiliary engines. Therefore, the obtained results can be implemented on any vessels and any diesel engines.

 

4. The paper discusses the use of B10 and B30 biodiesel blends. Were any other blends (e.g., B20) considered? Explain the reason

We have added the following information.

²⁴Currently, marine diesel engines use biofuels with a maximum FAME content of no more than 30%. B30 is such a fuel. B10 fuel was used to expand the experimental data array and determine the effect of biological components of fuel on diesel engine performance.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

1.    I believe that this study is a good result of applying biodiesel to actual marine diesel engines.

2.     Please describe the specifications of each engine and measuring equipment.

3.     Please add figures for the installation of each engine and measurement equipment.

Comments on the Quality of English Language

None.

Author Response

2. Please describe the specifications of each engine and measuring equipment.

We have added the following information.

³²The MAN-B&W Diesel Group's 5S60ME-C8 main engine transmitted its power to the fixed-pitch propeller using a direct drive. Depending on navigation conditions and the commercial assignment for the voyage, the operating modes of the 5S60ME-C8 MAN-B&W Diesel Group diesel engine were 65–95% of the rated load. During starting and shunting modes, the diesel engine was operated at loads of 10–50%. The main engine could be operated using fuel with a viscosity of up to 700 sSt at 40° C.

The auxiliary engines 6DL-16 Daihatsu Diesel were the drive for the electric generators and were part of the ship's power plant. Their power was sufficient to ensure all operations on the vessel in all modes (emergency, mooring, cargo, normal). In this case, either one of the three engines or two engines were in operation. In this case, they worked in parallel mode. Depending on the load on the ship's power plant, the operating modes of the 6DL-16 Daihatsu Diesel engines were 50–80% of the nominal load. Operation of auxiliary diesel engines was possible using fuel with a viscosity of up to 500 sSt at 40° С.

 

³²All measuring equipment that ensured control and regulation of the diesel engine operating parameters was located in the central control post of the engine room.

 

3. Please add figures for the installation of each engine and measurement equipment.

We have added the following figures.

³³A general view of the main engine 5S60ME-C8 MAN-B&W Diesel Group is shown in Figure 3.

³³Figure 3. A general view of the main engine 5S60ME-C8 MAN-B&W Diesel Group

³³A general view of the auxiliary engines 6DL-16 Daihatsu Diesel is shown in Figure 4.

³³Figure 4. A general view of the auxiliary engines 6DL-16 Daihatsu Diesel

³³Figure 6. A the central control post of the engine room

³³Figure 7. Main and auxiliary engine control computer

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Thanks to the authors for responding to comments and correcting them in the revised manuscript