Future Power Train Solutions for Long-Haul Trucks

Round 1

Reviewer 1 Report

Please look at the comments in the attached file,

 

the middle part of the paper could be more clearly structured and, maybe, shortened by removing some parts not related to the main theme of the paper.

 

Overall the review article is worthy of publishing, but it requires some finalization, please re-read and edit some of the statements and sentences, please make the terms and expressions more clear.

Comments for author File: Comments.pdf

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 2 Report

This paper presents a thorough and interesting review of the issues surrounding decarbonising heavy duty transport, considering both fuels and powertrains. In general, although the work gives a thorough coverage of the references involved, it can be difficult to draw conclusions from the long descriptive passages in the paper. I think that this would be helped by the use of summary tables, graphs etc to point the reader to the key conclusions from the review. I think that the work would also be improved by a comparison of the options for Heavy duty trucks in Germany (as an example) to form a conclusion to the paper.

Specific comments are below. Please note that there are a few occasions where the technical English is not quite precise enough to convey the meaning properly. 

58 – could also mention autonomous driving technologies like platooning

116 – biofuels can be combined with and electric drivetrain using a conventional engine so I don’t understand the logic of this sentence, similar comment for line 127, is the author thinking of on board reforming to supply hydrogen for a PEM fuel cell – there is a lack of precision in  the language here which is confusing

142 - there is extensive coverage of the development of H2 engines in the literature, I don’t understand the inclusion of ICE with DME and exclusion of ICE with H2?

162 – the authors miss an important distinction between LCA  and WTW emissions in this discussion, with LCA including vehicle production and disposal emissions. This section should be updated to clarify this

193 – its not clear what transport refers to in this figure – is this tonnes freight?

217 – what does crowd behaviour mean?

378 – label chemical compounds in Figure 5, it’s unclear what the text insert in the left hand figure refers to

497 – again the chemical compounds should be labelled in this figure

716 – does the author mean single cylinder engine, rather than single stroke?

728 – what does high emission gas recycling mean? EGR?

730 – single strike – should this be single cylinder?

781 – Limitations in forecourt infrastructure (ie number of pumps) limits the number of blends that can be offered, which makes backwards compatibility with the vehicle fleet important, this can be a significant barrier to adoption – eg introduction of higher blends of ethanol in gasoline

810 - The title of this section (and similar sections) should be changed to powertrain technology and vehicle availability as not all technologies have engines

817 sound pressure level A weighted (not rated) no indication of how favourable it is, just a filter frequency profile.

841 would a diagram be easier to understand

862 how is the CO2 reduction calculated – what grid carbon intensity is assumed, battery size for the trucks etc, is it on a lifecycle basis?

896 – what are the different stages, what do the annual operating costs include?

972 – this is a very in depth section, perhaps some charts might help to draw conclusions from this material

978 – need to clearly define the meaning of hybrid catenary systems (is it a truck with a battery and Overhead line charging, or a diesel engine or rail/truck hybrid system)? I think that catenary systems in development are a purely electric solution, so there is a battery and overhead charging with no diesel engine.

982 – this sentence doesn’t make sense to me

1020 – dual fuel engines also use more diesel at low speed transient conditions, so urban operation can lead to low natural gas substitution levels, see also line 1043, I think that substitution levels lower than 60% are sometimes achieved.

1062 – the engine emits up to 15% less CO2, rather than consumes

1326 – can the author state what tax and VAT levels are assumed

1400 – it’s unclear what the additives listed are – Lubrizol is a company?

1429 – Diesel fuel injection pressures ~2000 bar are common for Euro VI

1517 – higher EGR can also lead to lower brake thermal efficiency

1543 – better fuel additives?

1545 – could the author define HC SCR?

1627 – the risks with DME are not eliminated, rather reducees – the authors have stated the need for different fuel additives to reduce wear

1662 – zero tailpipe emissions

1671 – hydrogen engines can have similar efficiency to fuel cells,  based on the commonly quoted range of efficiency for FC of 40-60%, so should they be included?

1678 – a larger, heavier fuel cell system will be needed due to increased power output needed

1683 – could the author use SI units in this paragraph

1697 – energy is not transmitted by the battery, it is stored in it

1827 – zero tailpipe emissions

 

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Now the structure of the paper is clear,

the sentences have also become more sound and exact.