2-Stroke Scavenging in Conventional and Minimally-Modified 4-Stroke Engines for Heavy Duty Applications at Low to Medium Speeds

Round 1

Reviewer 1 Report

The author presented the transformation of a standard 4-stroke cylinder head into a torque-improved and gradually more efficient 2-stroke design. Calculations, flow simulations, and visualizations of experimental flows in relevant geometries and time scales were undertaken to indicate the feasibility, followed by a small engine demonstration. The method is very clear and useful. I would like to recommend this paper to be published in journal Inventions after a minor correction:

-         The description of “obstruction angle” could be more obvious.

Author Response

Dear Editor, dear Reviewer,

thank you very much for the generally positive valuation of the manuscript.  Please find below detailed answers to your remarks and questions.

The changes in the revised manuscript were marked in yellow (attached).

In addition to your comments I had to correct Eq. 4: As for 4-stroke, the relative friction must refer to the internal gross power and not to the external net power. The corresponding Fig. 4 in the previous manuscript was already in accordance to the corrected Eq.4.

Furthermore, I corrected some misguiding figure references. Lines 317 “Fig. 5”, 345 and 346 “Fig. 5d”, and 347 “Fig. 6e”.

I hope to satisfy your question and concern and thank you again!

Reviewer 1

The author presented the transformation of a standard 4-stroke cylinder head into a torque-improved and gradually more efficient 2-stroke design. Calculations, flow simulations, and visualizations of experimental flows in relevant geometries and time scales were undertaken to indicate the feasibility, followed by a small engine demonstration. The method is very clear and useful. I would like to recommend this paper to be published in journal Inventions after a minor correction:

-         The description of “obstruction angle” could be more obvious.

Answer: The obstruction angle α is introduced in line 131, along with Fig. 2: „The effectively blocked circumference is herein denoted as the obstruction angle α. The experimental jockey in Fig. 2c results to α ≈ 120°.“

Author Response File: Author Response.docx

Reviewer 2 Report

Aim of this work is to analyze the performance of a 4-stroke engine minimally modified in order to operate as 2-stroke engine at low to medium speeds. The subject is present in open literature, therefore it can be considered a "hot topic" for internal combustion engine field. The following points shall be addressed in order the paper to be eligible for publication:

Line 30: why “lower dead point” instead of “Bottom Dead Center, BDC”? the same applies later to “cubic capacity”: is this equivalent to “displacement”? if so, why not to use the more common “displacement”?

Fig. 1(b): “real” is generally replaced in literature by “geometric”

Line 89: please comment more extensively the statement “where the limited time … is less critical”

Line 165-166: the assumption to double the energy losses due to the cycling at double the speed is questionable, given that the energy losses usually depend on the square of the rotational speed; please comment

Figures 5f) and g): the difference between these two figures is not clear

Finally, the Authors state: "As previously suggested [9], the engine could be modified to be switched between 2-stroke (for 394 low rpm) and 4-stroke (for high rpm)"; in my opinion, I would have approached the problem in order the engine to operate in an opposed way, i.e. 4-stroke at low-medium speed and load and 2-stroke elsewhere, in order to obtain some downsizing as well. Can you please comment on this?

Author Response

Please see the attachement

Author Response File: Author Response.docx