The paper present the development of a closed-loop control algorithm for a 2-stage turbocharging system aiming to optimize fuel consumption, by minimizing pumping losses, and transient response, by minimizing time to reach a charging pressure set-point. The task is challenging, as the two objectives require counteracting management of low and high pressure turbocharging stage and the relevant turbine control device, i.e. waste-gate position. The subject is interesting, as the number of application of turbocharging technique to gasoline engines is growing, aiming at the reduction of fuel consumption and CO2 emissions while improving performances. Anyway, the paper is not acceptable in its present version, as different aspects need to be clarified. The term “over-actuation” is widely used in the manuscript. Though its meaning is arguable, a definition should be included. It must be specified the relationship between the waste-gate actuation signals and the relevant waste-gate positions, that is, for example, if uwg,hp=100% corresponds to a complete closure of the waste-gate of the high pressure turbine. Lines 98-105 and 117-124: text is exactly the same. Figure 3: a better choice of colors representing the different levels of engine speed should be done to improve the readability. The indication of graph for high and low pressure stage should be clearer, as it can only be derived by the mass reported on X axis. Moreover, no indication on waste-gate combinations can be observed in the figure. This also prevent to fully understand the statement at line 151. Line 155: the discussed figure is number 4, not 6. Line 163: the statement should be clarified in terms of waste-gate positions (closed-opened) of the two stages. Line 164: the statement “… this hold true even for small mass flows” should be proved with an example from fig.4. Figure 5: a better explanation has to be included. The step input start after 1 s, this should be specified when giving values of t95 (lines 180 and 181). What do the two curves represent? What is Dpchar, norm? There is probably an error in the indication of the parameter shown in the last two graphs, as one should be the actuation signal of the low pressure stage waste-gate. Terms included in equations 17, 23 and 29 should be explained, taking also into account that they are not included in abbreviations and indices. Line 245: what does “sates” mean? Line 255: please check the statement, as the controller reducing pumping losses should mostly use the low pressure stage. Figure 7: as in figure 5, there is probably an error in the indication of the parameter shown in the last two graphs, as one should be the actuation signal of the low pressure stage waste-gate. More important, following the text explanation (lines 259-264), the third strategy, optimizing both the objectives, should reach strategy 1 after the transient in order to reduce fuel consumption. It is not clear (and is misleading, observing the figure) why it becomes strategy 2 in figure caption. The presented transient response is a quite simple case study: what about the controller behavior on a driving cycle or in real world conditions?
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Authors worked to revise the first version of their manuscript, but there are still several open issues. - Model validation: it is not enough to write (lines 119-120) that NOx calculated values were validated through measurements on the test bench. The comparison should be presented, while giving information on instruments and test rig. - Remark “there is no overlap between zones of maximum temperature and NOx levels”. Response: “The formation of NOx is lag compared to the variation of temperature”. No details are included in the manuscript about this point. - Fig.11: I’m still of the opinion that mean temperature curves are useless and misleading as I don’t’ agree with the authors’ response “mean temperature curves are still a reference to analyze the extent of the reduction of combustion temperature”. - The last remark on PM emissions aimed to check if PM calculation were made by the authors and to include some considerations on this aspect in the manuscript. None of these answers were given.
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The paper presents a numerical study on the application of Miller cycle to a turbocharged two-stroke marine diesel engine. Different timings of exhaust valve closure were investigated, while 2-stage turbocharging and exhaust gas recirculation were also considered. 1-D and 3-D simulation models were used to evaluate NOx emissions, fuel consumption and other engine parameters. Though the subject is interesting, the manuscript has to be revised in order to be accepted.
- Introduction, line 39: NOx generation is related to maximum combustion temperature and O2 availability, but only the first aspect is mentioned.
- Introduction, line 63: what about PM penalty due to EGR application?
- Figure 1: caption is too generic. It is stated that 1-D simulation allowed to define initial conditions for 3-D calculation (line 80), but in the scheme results are also derived from 1-D model. Please better specified this point.
- Table 2 and fig.4: are data referred to full load condition? No information is given about this point.
- Line 101: “TDC is defined as 360 °CA”, but TDC shown in fig.4 is at 0 °CA.
- Line 115: two injectors are quoted, but no information is given on fuel injection system in Table 1.
- Lines 117-118: it is well known that the combustion temperature influences NOx formation. Moreover, why figure 6 is related to a short interval (from 364 °CA to 378 °CA) with a 2 °CA step, while figure 7 show results for a long range (from 370 °CA to 400 °CA) with a 10 °CA step? It is not possible to compare graphs, except for 370 °CA. In this case, there is no overlap between zones of maximum temperature and NOx levels.
- Line 144: what is CF?
- Figure 11: mean temperature curves are useless, as they don’t allow to describe the strong variations of in-cylinder temperature. Moreover, please take into account that presented values are below or very close to 1600 K, which is a common threshold to consider NOx formation.
- Figures 12/13: as for figures 6/7, there is no overlap between zones of maximum temperature and NOx levels.
- Table 3: power reduction due to the application of Miller-cycle is not considered in the discussion. Which are the reduction percentages of this parameter referring to the baseline condition? NOx variations are referred to volumetric concentrations or to specific emissions?
- Line 165: please justify the statement on 2-stage turbocharging influence on charger efficiency and fuel economy (authors calculation or references).
- Figure 15: authors should justify observed results. What about engine power?
- Line 177: please check figure 15 caption.
- Figure 16: no information is given about the selected EGR layout.
- Line 194 (caption of figure 17): what does it mean EGR rate 5 and EGR rate 10? Which is the measuring unit of EGR rate and how was EGR rate defined and computed?
- Figures 17/18: see comments on figures 6/7 and 12/13.
- Figure 19: one of the symbol is not reported in legenda (red triangle with cyan contour).
- Line 217: what is BFOC?
- What about PM Emissions?
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This paper addresses the very important topic of public engagement in research, with a particular focus on energy. The authors categorized the role of the research organisations and researchers in these public engagement projects into five modes, namely, discussing, consulting, involving, collaborating, and supporting and discussed the characteristics of these modes by utilizing some actual examples to illustrate the main points. This paper would make a valuable contribution to the current discussions in this field by differentiating the different modes of public engagement in energy research and identifying a variety of methods and tools available for facilitating the participation of stakeholders.
One issue that would be very critical in promoting public engagement in research is the incentives to researchers in academia. While researchers are encouraged to commit themselves in public engagement, they are at the same time under increasing pressure to publish papers in good journals. Hence it would be crucial to have appropriate incentive structures and frameworks so that academic researchers are encouraged to get involved seriously in interactions with the public. This dimension of institutionalization has been discussed in the literature, including such work as follows:
Yarime, Masaru, Gregory Trencher, Takashi Mino, Roland W. Scholz, Lennart Olsson, Barry Ness, Niki Frantzeskaki, and Jan Rotmans, "Establishing sustainability science in higher education institutions: towards an integration of academic development, institutionalization, and collaborations with stakeholders,"Sustainability Science, 7 (Supplement 1), 101-113 (2012).
It would be very useful if the authors could also discuss how scientists and engineers in academia actually thought about public engagement and responded to societal expectations and how they tried to make a balance or create synergies between the conventional research activities mainly targeted to produce publications and those activities for public engagement. It would also be very interesting to see how the outcomes of various types of activities for public engagement were evaluated and what benefits and difficulties the researchers felt in getting involved in close interactions with various stakeholders in society.
Also it would be important to think about educational impacts of these activities for public engagement on students, particularly master's and doctoral students whose research work is involved in interactions with stakeholders, as the objectives of education, research, and public engagement would not necessarily be compatible with each other.
By considering these dimensions, it would be possible to draw useful lessons and implications for establishing policies and institutional environments in which public engagement by researchers would be promoted further in the future. Perhaps it might be necessary to introduce some changes in the criteria for evaluating the performance of researchers in the process of hiring and promotion in academia.Reviewed by
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Overall Recommendation ( ) Accept in present form (x) Accept after minor revision ( ) Reconsider after major revision ( ) Reject English Language and Style ( ) English language and style are fine (x) Minor spell check required ( ) Extensive editing of English language and style required ( ) I don't feel qualified to judge about the English Language and Style Comments and Suggestions for Authors Please see the changes I am suggesting in the attached file. Just minor changes.
peer-review-893569.v1.docx Comments for Editors (will not be revealed to authors) This can be published after taking my comments inserted as track changes into consideration.Reviewed by
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The paper presents the design of a controller for an EGR system to be applied on a turbocharged diesel engine, suitable for transient operation. The controller is developed and validated in Matlab-Simulink and GT-Power, while is finally tested on an engine. Though the subject is interesting, even if EGR control is a topic with a long history, the manuscript has to be enhanced in order to be accepted.
In particular: - Which is the final goal of the development of a new EGR controller, that is, which types of engine is the controller suitable for? This aspect is fundamental, because a number of papers are available for EGR systems control in the automotive field (see for example Shutty, Benali, Daeubler, Traver, Air system control for advanced diesel engines, SAE paper 2007-01-0970) and many problems have to be considered when controlling EGR system, first of all the interaction with the turbocharger, so it should be explained why a “simple” controller is required. - The model description is quite long, if referred to the overall manuscript length, usually it can be included in an Appendix section. - No information is given on the tested engine, while it should be specified if the controller is suitable for a high pressure EGR system only or it can be also applied to a low pressure EGR system (or even to both). - Equations 13 and 14 – line 130: four efficiencies are presented in equations, while only two are explained in the text. - Coefficients for matrixes A and B are obtained for one operating condition: what does it happen if this condition is changed in a significant way in engine speed, load and/or EGR rate? A similar remark: are the considered transient tests applied for the experimental validation sufficient to validate the designed controller? What if intake oxygen mass fraction is significantly lower than 21.3%, which is the minimum level considered in the experimental validation? - Lines 225-230: considerations on linear model are somewhat obvious. - There are a number of statements which are difficult to read and need to be rephrased, but “fuel is being completely combustion” (line 344 and 356) have to be absolutely avoided (for its English, not for the assumption). - Please check values in Table 2: error in the last line is wrong (1.23%, not 0.24%). - I don’t agree with the statement in lines 368-369: “… it is easy to implement for (probably authors mean four) other sensors in engineering practice”. Due to cost increase, each sensor to be added is subject to a strong discussion with engine manufacturers.