Modeling and Evaluation of Oxy-Combustion and In Situ Oxygen Production in a Two-Stroke Marine Engine
Round 1
Reviewer 1 Report
The goals and outputs of the paper
The aim of this paper is to simulate the 2-stroke marine diesel engine with oxy-fuel combustion. The baseline design simulated by VEMOD was calibrated against the manufacturer data. A comparison was then conducted between the baseline design and the designs with different configurations of the oxygen system production.
Comment on the originality, relevance, and long-term impact of the paper
The presented study is original and new to the literature. The provided information is useful for the community. However, the submitted manuscript needs major revisions to have an archival value. To be eligible for publication, at least one of the following three items must be completed.
1. The presented paper does not give any details of the engine data, inputs, or outputs (mentioning that the engine data is confidential, even for the very common data such as engine power and torque). With its current form, the study is not repeatable, or the data cannot be used by the readers for further research studies.
2. The model is just giving screenshots for the layouts without providing inlet/outlet conditions, or the equations running in the background. The readers will have no idea how those calculations were conducted. There was only a screenshot of the black-boxes and normalized results. Also, the study needs correlation with the experimental data, at least for one or two of the outputs.
3. Throughout the article, the authors emphasize the importance of NOx production and emission levels. However, I couldn't find any clear results for the comparison of NOx production in the results and discussion section. As the study was focused on emission rates, the authors should provide more comparative data by including GWP for hazardous exhaust gases in the results and discussion section.
Please see the following items for further comments.
· Figure 1 is pixelated. Please improve the quality of the figure. It would be also better to produce a new figure for this paper instead of using directly the one in the literature.
· Line 111. In the first instance, the baseline engine model was configured in the software to be used during the study.
à Please provide the software details here. (name, the solver type (i.e. solving mathematical models, or using different numerical methods?) Is the software commercially available or in-house developed? It would be better to mention these details at this stage. The name should also be provided in the introduction and abstract so that readers will have an idea before Section 2.1).
· Line 118. The marine engine evaluated in this study is a two-stroke, 8-cylinder CI engine.
à Please provide more information about the evaluated engine. (The model of the engine, maximum engine operation speed, power and torque, volume, fuel injection system etc.). A visual for the real engine will be beneficial.
· Line 124. This model was replicated in the simulation software 0D-1D Virtual Engine Model
è So basically, the software is solving analytical models, not using numerical methods. Could you please confirm? The authors should provide more information for the solver running in the background since the software is an in-house developed tool.
· Figure 2. Please add explanations for all abbreviations in the graph in ‘Abbreviations’ section (Cyl etc.).
· Figure 3a. How come power and torque curves are confidential? They are the main engine performance parameters for the end users, and no one will procure an engine without knowing its power, torque and fuel consumption levels.
· Figure 3a. The curves are not clear to me. Why are dots used as markers in all curves? Please use different type of markers. So for the comparison of VEMOD and manufacturer, only BSFC compared – or power-torque also compared but they are identical and cannot be observed from the graph?
Also, I believe the manufacturer means here that the baseline design simulation data is by the manufacturer. Please confirm this and give precise information.
It will be better if the authors mention ‘Baseline design – Manufacturer simulations’ and ‘Baseline design – VEMOD simulations’ in the graph to be more precise (if the provided data for manufacturer means manufacturer simulations).
In the following parts, it has been indicated that VEMOD model is having better accuracy. In order to make this comment, experimental correlation should be provided. I am sure there is data for BMEP, Power, and torque measurements, rather than manufacturer simulations (if the provided manufacturer data is not experimental).
Also if the manufacturer data is from simulations as indicated Line 118., ‘The engine manufacturer provided a reference model of the ship propulsion system which…’ details of their solver should also be provided. (analytical, using numerical methods etc.).
· Figure 3b. I believe the curve provided is the turbine supplier map. Please provide this information in the graph. And again, what is the basis for the manufacturer data? Experimental, specs, simulation of the baseline design? Please provide more precise information.
· Figure 3c. Same for Figure 3c. What is the basis for the manufacturer data? Experimental, specs, simulation of the baseline design? Please provide more precise information.
· Figure 4 thru 6. Please provide precise information for the stations in this graph. I can identify turbochargers, but what are the other stations for the system? Just symbols are given, and the system information is not clear. Also, no information has been given for the inlet/outlet conditions, or the equations running in the background. These are just the picture of the model like the boxes in the Simulink window. More information should be provided for the equations used to have an archival value.
· Figure 13. Please correct the typo ‘Serie’ in the graph.
Author Response
Please find the reply in the attached document
Author Response File: 
Author Response.pdf
Reviewer 2 Report
1. The reduction in NOx production due to nitrogen in the air is just one of the sources. There is no discussion of other sources of NOX.
2. Lack of explanation in the text of the abbreviations HFO and MDO. Abbreviations are understandable to a small group of readers, so they should be explained in the text. This will improve the clarity of the article.
3.Fig.1 shows e-electron migrations. Is an electric potential difference needed for a chemical reaction to occur?
4. rr. 74 p. 2. How was define the partial pressure responsible for the separation of oxygen from the air? Is it static pressure?
5. Fig 3. a no curves for torque and power for the reference model.
6. Fig.1 no explanation of 1, 2... etc.
Author Response
Please find the reply in the attached document
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors have been addressed most of the issues. The paper can be accepted in its present form.
