Examination of the Influence of Alternative Fuels on Particulate Matter Properties Emitted from a Non-Proprietary Combustor

Round 1

Reviewer 1 Report (Previous Reviewer 1)

Comments and Suggestions for Authors

The paper can be accepted for further publication based on current revised status.

Author Response

The authors thank the reviewer for their support. No comments to address

Reviewer 2 Report (Previous Reviewer 2)

Comments and Suggestions for Authors

First of all, I would like to acknowledge the effort made by the authors in the detailed and extensive answers, and the effort to include some modifications and clarifications in the document. I consider that the quality of the paper has been improved, and now it could be published.

Author Response

The authors thank the reviewer for their support. On balance of reviewers 1 – 3, the authors believe the manuscript is in an acceptable state for publication and request the editors to decide if further modifications are required, beyond the proof reading and reference checks. Reviewer 1 has no comments or recommendations for the manuscript, reviewer 2 only has a "could be improved" for the methods and results.  Importantly both reviewers 1 and 2 believe the conclusions are supported by the results and the introduction is sufficient and both state the manuscript is acceptable for publication.

Reviewer 3 Report (Previous Reviewer 3)

Comments and Suggestions for Authors

This paper aims to propose a novel combination of Positive Matrix Factorization (PMF) and high resolution AMS analysis to evaluate the impact of fuel composition of volatile particulate matter (vPM) emissions on an open-source design combustor rig. However, there are several s requires to be corrected.

Comments on the Quality of English Language

 Minor editing of English language required

Author Response

On balance of reviewers 1 – 3, the authors believe the manuscript is in an acceptable state for publication and request the editors to decide if further modifications are required, beyond the proof reading and reference checks. Reviewer 1 has no comments or recommendations for the manuscript, reviewer 2 only has a "could be improved" for the methods and results, whereas reviewer 3 suggest there must be some improvements.  Importantly both reviewers 1 and 2 believe the conclusions are supported by the results and the introduction is sufficient and both state the manuscript is acceptable for publication.

Reviewer 4 Report (New Reviewer)

Comments and Suggestions for Authors This manuscript discusses the issue of PM2.5 emissions from biomass fuels.  It is hard to read.  Due to the lack of characterization, only one PM detector sensor was used, leading to a superficial disscussion. For the particulate matters, add some SEM images? analysize the partical sizes distribution? give some information about elements analysis? While only a vague PM concentration is given here, and derives some curves with obvious errors. The fuels chosen also does not show any typical characteristics of alternative fuels.

 

I think you shall revise it to be more readable.

Author Response

The authors believe reviewer 4 has either not read our manuscript properly or has failed to understand it. In detail:

• Reviewer 4 summarises the manuscript as “issues of PM2.5 emissions”. PM2.5 is not mentioned in our manuscript. The AMS, LII and MSS are PM1 instruments, shown clearly in table 2, and the majority of the collected data is PM0.1, as can be seen in SI:Figure 4 SMPS data. The sampling system negates larger particle transmission.
• “Due to the lack of characterization, only one PM detector sensor was used”. This is completely false. The PM sensors used in this manuscript are:
  • Aerosol mass spectrometer
  • Several number-size distribution measurements
  • nvPM mass detector (MSS)
  • Several nvPM and TPM number counters
  • A semi-continuous OCEC analyser.

These are all detailed in table 2.

• The reviewer is suggesting adding SEM images from a project that is completed, which is impossible, and the manuscript is not about particle morphology.
• “analyse the particle sizes distribution?” The SMPS data has been extensively analysed and presented. In the SI, figures 1, 4, 5 and 10 are SMPS data with figure 4 showing the size distributions per fuel for all runs. In the manuscript, SMPS data is used in Figures 3 and 4 and the associated discussions and is discussed in section 2.5.
• “give some information about elements analysis?” The fuel properties have elemental analysis and the AMS high resolution data presents the elemental C_xH_y components of the 2 PMF factors of the vPM, something unstudied in prior literature.
• “While only a vague PM concentration is given here, and derives some curves with obvious error”. The authors have extensively analysed all PM data from all sensors, attempted to find correlations with the fuel properties, performed Positive Matrix Factorisation on AMS data, performed detailed high resolution AMS analysis, performed a large correlation analysis on all the AMS data, and looked to the literature to explain the results. There is more than a “vague PM concentration” presented. We strongly disagree with this statement
• The reviewer says the fuels chosen do not show any typical characteristics of alternative fuels. This is completely false. As stated in the manuscript, the two SAF fuels are “an Alcohol-to-Jet synthetic paraffinic kerosene (ATJ-SPK), with a composition entirely of alkanes, and A-HA; a Catalytic Hydrothermal Conversion Jet (CHCJ) fuel”, both recognised SAF fuels. Plus, blends of SAF-HEFA fuels and JetA1.

 

Round 2

Reviewer 4 Report (New Reviewer)

Comments and Suggestions for Authors

It's the first time I've seen such a grumpy author, hehe. Well, since I understand it completely wrong. Then the suggestion to write the paper a little more readable probably has a little sense. After all, I believe I have a little review experience, and this is the first time I completely can not understand it. 

 

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper has examined changing aerosol properties as a function of changing fuel characteristics. Diaromatic content, viscosity and molecular weight was hypothesised to explain some of the discrepancies in particle number and mass concentrations. The composition of the organic vPM was also shown, and the composition varied very little as a function of fuel composition at all rig conditions examined. The detection of a QOA factor emitted from a RQL rig has been replicated. Some interesting conclusions have been obtained.

Different methods for examining the influence properties are studied. What is the advantages of the proposed method in this paper?

More application examples can be provided to verify the conclusions.

Comments on the Quality of English Language

Minor editing of English language required

Reviewer 2 Report

Comments and Suggestions for Authors

Most of the paper is comprehensive and detailed, and most of the results are coherent with previous knowledge. In general, I consider it an interesting and well-written research. Nevertheless, some issues need additional information. It does not imply an outstanding innovation in the approach or methodology in this research field; and the contributions that this research makes compared to previously existing ones should be highlighted. In this sense, you should emphasize the innovation in your approach and focus the analysis on novelties.

The methodology employed in the sample collection process, as well as the dilution process, the nine fuels used, and the instrumentation utilized, are generally clear and well-explained. Regarding the document's structure, there are areas for improvement, such as the ‘repetition’ of sections 2.4 and 2.6, both addressing “instrumentation.”. In my opinion, two primary areas crucial for enhancement are:

Firstly, concerning experimental uncertainty. A comprehensive understanding of experimental uncertainty is needed to maintain the integrity and credibility of engineering and scientific research. It is essential to note that the graphs do not depict data with their associated uncertainty ranges. In any experimental study, careful consideration and analysis of measurement uncertainty, repeatability, and error propagation are vital. This aspect should be addressed for improvement. Overall, representing experimental results with a validity range is integral for maintaining scientific rigor, supporting informed decision-making, and fostering a culture of transparency in research practices. As in any experimental study, the measurement results should be shown with their analysis of uncertainty study included. Additionally, you should qualify the oscillations, standard deviation, fluctuations, etc. You must include the uncertainty study, please.

Secondly, there is a need to enhance the mathematical rigor in results analysis. I perceive a lack of a comprehensive study quantifying the weight of each considered factor. While this study serves as an initial phase for measuring various fuels, a rigorous analysis of these results is yet to be conducted. The discussion should interpret findings in relation to existing literature, emphasizing the study's novelty and importance. Acknowledging limitations and potential biases adds depth to the interpretation. Practical implications, such as environmental and public health considerations, should be explored, along with recommendations for future research or policy applications.

Reviewer 3 Report

Comments and Suggestions for Authors

In this paper the influence of alternative fuels on particulate matter properties in an aircraft gas turbine engine was investigated experimentally on a non-proprietary combustor rig. The effects such as composition and concentration on the number and mass concentration of PM were investigated and discussed. However, the article requires a major revision in the structure and language.

1. The section of introduction is short of the reviews of recent developments on the related studies including discovery, methodology, technique, theory and so on.

2. All the tables should follow the MDPI format, and please check the details from the website.

3. The author mentioned that “Because of these considerations, the relationships shown are likely representative of the engine exit plane’s particles,...” But it is not sounded according to the description of sampling system alone without the description of combustor rig setup. Please add the illustration of the combustor rig setup.

4. It is difficult for readers to identify the discussions from other view points of tremendous references. Usually, references should be reviewed in the section of introduction. Few references can be applied for supporting the conclusions.

5. The sections of results and discussions should be merged on purpose to judging the authors’ view points from corresponding results.

6. Conclusions should be clear and concise. Please rewrite the section of conclusions with several clear points with quantitative results.

7. Logical confusion widely exists in the section of discussions. For example, “Except for TP1, diaromatics had a greater correlation than monoaromatics with number concentrations at each test point, despite monoaromatics having a stronger correlation with the averages across conditions” in Line 457 to Line 460. Does monoaromatics have a stronger correlation, or not?

8. Several errors requires to corrected. For example, “1-16 bara” should be “1-16 bar” in Line 113 and “have strong correlation” should be “have a strong correlation” in Line 398.

Comments on the Quality of English Language

A moderate editing of English language is required in scientific experssion and grammatical error correction