Performance and Exhaust Emissions of a Spark Ignition Internal Combustion Engine Fed with Butanol–Glycerol Blend
Round 1
Reviewer 1 Report
In this manuscript, the authors study the performance and emissions of a positive ignition internal combustion engine fuelled with a mixture of butanol and glycerol. The results obtained are compared with those of the same engine powered by gasoline and by butanol only which, therefore, are used as reference fuels.
The manuscript is clear and well written. However, before publication, I think it is useful for the authors to clarify two points in particular.
- How did the authors determine the percentage of glycerol to be used in the blend? Is it an optimal value, the result of analyses carried out on different possible mixtures, or a simple trial value, or is this percentage the result of a reasoning based on the current or possible production potential of the components of the mixture? In particular, this last point should be commented upon, if we consider the possibility of replacing part of commercial gasoline with this combustible mixture.
- The authors highlight the comparison of the performances obtained with the chosen mixture with that of gasoline fuelling. Therefore, in the submitted study, they seem to consider mainly the automotive field, as can also be learned from the abstract where it is said that this particular combustible mixture could be directly substituted for commercial gasoline. However, the engine chosen for the tests, whose unit displacement is characteristic of a light duty engine with high performance, was tested at a rotational speed of 600 rpm. Automotive engines never reach such rotational speeds, but operate at higher values. What is the reason for the choice of the regime for experimental tests, which is not representative of real use, if not during the engine start-up phases? It is unclear, in fact, why the engine should follow the conditions for octane number measurements in the CFR engine, when the focus is on emissions and performance for automotive application. The authors should clarify this aspect.
There are also some minor changes, including:
- line 131: the brackets at reference 7 are missing;
- figure 3a, pressure gradient plots are missing.
Author Response
Responses are in the file attached.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
- [Line 28] The beginning of the introduction is given without references or explaining the information source.
- [Line 45] How will you explain that today the production cost of the by-product glycerol is about 0?
- [Line 178] In my opinion, the list of fuels used in tests may need to be separated from the text "The methodology for the investigation ..." [Line 169]. You just need to list them in a separate line.
- [Line 211] The figure number does not appear.
- [Line 207] The equipment is described sufficiently. The methods could be described more detailed.
- [Line 306] The figure number does not appear.
- [Line 333] In my opinion, Fig. 4a and 4b could be placed next to each other.
- [Line 398] How many repetitions have been performed in the exhaust gas measurements? The values for CO, NOx, UHC emissions seems are given too precise. Emission in ppm is unreliable. It should be in [g/kWh] or in [g/kg. fuel] or for car in [g/km].
- A more detailed explanation of the reduction or increase in the exhaust components would be advisable.
- Think about the measured values in context with the accuracy of the used measuring devices. Consider this when formulating conclusions.
- State the scientific value (importance) of your contribution in the conclusions.
Author Response
Responses are in the file attaxched.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
I recommend accepting the article after editing.
