A Study on the Correlation of Factors Influencing the Cyclic Variation of Marine Natural Gas Engines

Round 1

Reviewer 1 Report

In this paper, a multi-point injection spark ignition natural gas engine is tested under different lean burn degrees to investigate the correlation between different parameters and cyclic variation, including accumulated heat release, combustion phase and burning rate. Here are the detailed comments,

1. As there are numerous previous research on this field of research, the novelty of this study should be further emphasized.
2. Introduction: The literature review is too long to be introduced in a whole paragraph. It is suggested to divide it into several paragraphs with a reasonable logic. The advantage and shortcoming of these studies should also be summarized.
3. What are the measure errors of the results? Error analysis needs to be explained.
4. Only these conditions are considered. Are they representative?
5. 6 and 7 are difficult to be understood, and it should be revised to become clearer.
6. Are there any physical meaning of the fitting data shown in Table 4 -10?

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

This reviewer considers that the study on the cyclic variation of marine natural gas engines has potential for publication, nonetheless some things still need to be addressed in order to improve the current work. The results are overall interesting, however in the current form the whole picture is not yet seen. Fundamentally corralating the maximum pressure and other responses (like combustion phasing, IMEP, and COV) provides less information than correlating the parameter the authors controlled, the lambda value. This is because both the maximum pressure and the other responses are a consequence of the in-cylinder conditions, which in this case are varied with the sweeped lambda value. In that sense, the analysis should be changed or amplified to include more insight into this lambda sweep instead of relating non-causal variables.

Revise the writing of the manuscript for grammar, form and some typos.
Improve figures' resolution and try to use 2D diagrams when only relating two variables during the discussion.
The authours should also find a attached to the review a PDF with more specific comments on grammar and specific sections.

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

Natural gas is the most successful alternative fuel for transport vehicles or ships. Lean burn is an effective way to inhibit the NOx emission, while cause the cyclic variation problem. The paper need revision before accept.

1. Why choose the China 2 emission standard?
2. In 3.3.2 and 3.3.3, CA50-CA05 is in highly correlated with flame propagation speed. The authors used them as different factors.
3. Some important references should be cited :

   Engine combustion and emission fuelled with natural gas: A review. Journal of the energy institute, 2019, 92( 4): 1123-1136.

Author Response

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Author Response File: Author Response.docx

Reviewer 4 Report

This article was a pleasant read which delves into the parametric analysis of combustion effects on the increase in cyclic variations when burning Natural gas under lean-burn combustion. The results derived from this article give key insights into which factors contribute the most to the cyclic variation which could be critical towards the design of lean-burn combustors for lower NOx emission. 

However, the article needs to elaborate a bit further on the following points namely:

Within the introduction, how does lean burn technology increase the specific heat capacity of the working fluid? 

Please elaborate more within the introduction on what are the requirements for NOx emission and what are the current emission level of emissions in marine engines.

Author Response

Thank you very much for your comments. The reply is in the attachment.

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The author did not answer all of my questions properly. They just give rebuttals to some parts of issues and have left some others.

Author Response

Thank you very much for your comments. The reply is in the attachment.

Please see the attachment.

Author Response File: Author Response.docx

Round 3

Reviewer 1 Report

The authors have replied my comments properly.