A Numerical Investigation on De-NOx Technology and Abnormal Combustion Control for a Hydrogen Engine with EGR System
Round 1
Reviewer 1 Report
L163 how is the in cylinder flow at the beginning of the simulation defined? It is only stated, that simulation was started at Intake closing, what neglects the in cylinder flow due to the intake stroke.
Line 195: How is the rapid compression period defined by the author?
Line 205: a figure with the change of the combustion phases due to ignition angle variation would be helpful for understanding the magnitude of the impact of different ignition angles
Line 209: there is no ignition delay visibly in the ROHR is there a reason? the ROHR starts immediately with the ignition timing.
Line 227 why is the oxygen content reduced? Only due to combustion, that’s clear, but there is also higher pressure and temperature reached than the other ignition timing will ever reach
Line 241: how can PFI fuel timing (-30°CA) influence, while intake valve is closed (-117°CA) or is ignition timing meant?
Line 239: is there same energy amount assumed due to the different A/F ratios?. That would mean, that different compression lines would be seen. Hence, when fuel amount is reduced, there is no wonder, why the ROR is reduced with leaner mixture.
3.1 is “state of the art knowledge on engine behavior, no new ideas are presented
Line 280: figure 7 and 8 is there 15% and 10% mixed up? Is EGR assumes as external or internal? It is not stated, why the step from 15 to 20% EGR nearly interrupts combustion, is there same ignition timing for all 4 operation points
The hole paragraph is a little bit confusing
In line 268 is same lambda 1,47 assumed, in line 302 is stated, that the oxygen concentrations reduced? What is correct? Or is there the energy amount also reduced? Is there same power output calculated?
Line 326 mixed up values of 15% EGRA and 1% EGR?
Line 354: how can LTC be used to control injection of Fuel? Or is combustion meant?
L395 the pressure curve is not rally fitting to the curves in figure 3 which has a leaner lambda (1,47 to 1,2 but both ignition 30°resp. 29°CA) but higher calculated peak pressure level.
In general it is missing, how the distribution of Hydrogen is calculated in the engine, esp. when at the end it is stated, that electronically controlled injection is helpful.
Also shoulb be clearly stated how the fuel incection shloud be desigend to improve control of unintentional combustion phenomena.
Also some values in the text and figures are mixed up, which makes some statements confusing.
Also a comparison and matching of (pre-) calculated simulation and measured date should be included.
Author Response
Please kindly see the attach.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The paper "A Numerical Investigation on Abnormal Combustion on a Hydrogen Engine with EGR System" presents an interesting analysis of the combustion process characteristics in a hydrogen engine under various conditions. The results presented in the paper were obtained on the basis of a developed three-dimensional (3D) model of a premixed hydrogen engine, agree with the known data and do not raise doubts. Below are some minor notes on the content of the paper.
- In the abstract and the paper, I recommend specifically writing what is the purpose of the work.
- The paper does not provide information about the temperature and pressure of the mixture at the inlet to engine, at which the research was carried out. The combustion process and engine power, as well as the temperature in the cylinder during the combustion process and NOx emissions, depend on their values.
- In section 3.4 "Effects of EGR system on Pre-ignition" does not provide specific results on the effect of EGR system on pre-ignition.
- There is not information in the paper about conditions under which the pressure diagrams were obtained (Figure 12) during normal combustion and pre-ignition.
- In section 3.5 "Measures to Controll Abnormal Combustion" the authors recommend using liquid hydrogen supply. This will reduce the temperature of the intake air. But the paper does not show the results of the intake temperature influence on the combustion process, pressure and temperature diagrams in the cylinder.
Author Response
Response to Reviewer 1 Comments
Dear Reviewer,
Thank you very much for your comments. The manuscript is entitled as follows: “A Numerical Investigation on Abnormal Combustion on a Hydrogen Engine with EGR System
” (Manuscript ID: processes-932239). We also wish to take this opportunity to thank the reviewers for their constructive comments and valuable recommendations. We have carefully revised the manuscript according to reviewers’ suggestion.
Our responses to the comments are listed below:
Point 1: In the abstract and the paper, I recommend specifically writing what is the purpose of the work.
Response 1: Yes, we fixed the abstract and Introduction of this paper:
Abstract: Nowadays hydrogen engines can use exhaust gas recirculation (EGR) technology to control the intensity of premixed combustion and reduce the NOx emissions. The study was aimed on improving of hydrogen engine NOx emissions and abnormal combustion by EGR technology. To reach the above goals, a three-dimensional (3D) CFD model of a single-cylinder hydrogen-fueled engine with EGR system was applied.
EGR system could delay the spontaneous combustion reaction of the end-gas and reduce the probability of knocking. The pressure rise rate was controlled and the in-cylinder hot spots were reduced by EGR system, which could suppress the occurrence of the pre-ignition in the hydrogen engine.
Introduction: Abnormal combustion of hydrogen-fueled engines has become a major problem that limits its utility [26]. At present, computational fluid dynamics (CFD) has developed rapidly [27,28]. It has become a reality to study the flow field characteristics, combustion characteristics, and abnormal combustion inside the cylinders of the hydrogen-fueled engines using high-performance computer simulation technology [29].
Nowadays hydrogen engines can use EGR technology to control the intensity of premixed combustion and reduce the NOx emissions. The study was aimed on improving of hydrogen engine NOx emissions and abnormal combustion by EGR technology.
Point 2: The paper does not provide information about the temperature and pressure of the mixture at the inlet to engine, at which the research was carried out. The combustion process and engine power, as well as the temperature in the cylinder during the combustion process and NOx emissions, depend on their values.
Response 2: We provide more information about the temperature and pressure of the mixture at the inlet to engine. The main modifications are as follows:
The experiment data of K5A hydrogen engine was under 100% load without EGR. The atmospheric pressure was 101.08 kPa, and initial air temperature is 304 K. The engine intake air temperature was 305.2 K, and the cooling water temperature was 348 K. The intake air humidity was 22.52 g/kg, and the relative humidity of intake air was 78.7%. Moreover, the gas used in the experiment contains 99.8% hydrogen and 0.2% other gases (N2, CH4, CO, H2O etc.). CFD model uses the same initial condition settings as the experiment data.
Point 3: In section 3.4 "Effects of EGR system on Pre-ignition" does not provide specific results on the effect of EGR system on pre-ignition.
Response 3: Yes, we failed to provide specific results, only provided the trend of reducing the pre-ignition. Pre-ignition occurs randomly, which is a big problem of hydrogen engine. This part of the experiment and simulation is too difficult to do, we have not finished this work.
Point 4: There is not information in the paper about conditions under which the pressure diagrams were obtained (Figure 12) during normal combustion and pre-ignition.
Response 4: Yes, a very good comment. We added the new conditions (Figure 12) during normal combustion and pre-ignition:
The condition of normal combustion is one case from Figure 7 under 2000r/min engine speed and 1.47 air/fuel ratio. The pre-ignition condition of the K5A hydrogen-fueled engine in Figure 12 was measured at an engine speed of 2200 r/min and an ignition timing of -29°CA aTDC while the air/fuel ratio was λ=1.2.
Point 5: In section 3.5 "Measures to Controll Abnormal Combustion" the authors recommend using liquid hydrogen supply. This will reduce the temperature of the intake air. But the paper does not show the results of the intake temperature influence on the combustion process, pressure and temperature diagrams in the cylinder.
Response 5: We deleted the liquid hydrogen supply part in section 3.5.
Thank you very much for the excellent and professional revision of our manuscript.
Yours sincerely,
Hao Guo
Author Response File: Author Response.docx
Reviewer 3 Report
Comments for A Numerical Investigation on Abnormal Combustion on a Hydrogen Engine with EGR System
This paper used EGR to control the abnormal combustion for a hydrogen engine. The topic was in the scope and writing of this paper was acceptable. Recommend accept after addressing the following issues.
The title of this paper should be revised. I try to find some abnormal combustion in abstract, but failed. After reading this paper, the focus is not abnormal combustion, in my opinion. See the first sentence of last paragraph of introduction, that is the main idea of this paper.
The following papers may be helpful for robust this topic, please cite in introduction if possible.
Gao J, Tian G, Sorniotti A, et al. Review of thermal management of catalytic converters to decrease engine emissions during cold start and warm up[J]. Applied Thermal Engineering, 2019, 147: 177-187.
In the validation section, it is better to provide more information about your experiment.
Figure 3: It seems unusual for the cases of 30 º. Why the value was higher than 0 for heat release rates after 20º CA? How about the engine load?
Why the authors choose the cases of 30 º where the position in crank angle of the peak in-cylinder pressure was before TDC? This situation will not happen in the process of engine calibration.
Author Response
Response to Reviewer 2 Comments
Dear Reviewer,
Thank you very much for your comments. The manuscript is entitled as follows: “A Numerical Investigation on Abnormal Combustion on a Hydrogen Engine with EGR System
” (Manuscript ID: processes-932239). We also wish to take this opportunity to thank the reviewers for their constructive comments and valuable recommendations. We have carefully revised the manuscript according to reviewers’ suggestion.
Our responses to the comments are listed below:
Point 1: The title of this paper should be revised. I try to find some abnormal combustion in abstract, but failed. After reading this paper, the focus is not abnormal combustion, in my opinion. See the first sentence of last paragraph of introduction, that is the main idea of this paper.
Response 1: Yes, we fixed the title of this paper:
A Numerical Investigation on De-NOx Technology and Abnormal Combustion Control on a Hydrogen Engine with EGR System
Point 2: The following papers may be helpful for robust this topic, please cite in introduction if possible.
Gao J, Tian G, Sorniotti A, et al. Review of thermal management of catalytic converters to decrease engine emissions during cold start and warm up[J]. Applied Thermal Engineering, 2019, 147: 177-187.
Response 2: Really a good paper. The References are added as follows:
- Gao J, Tian G, Sorniotti A, et al. Review of thermal management of catalytic converters to decrease engine emissions during cold start and warm up[J]. Applied Thermal Engineering, 2019, 147: 177-187.
Point 3: In the validation section, it is better to provide more information about your experiment.
Response 3: We provide more information about our experiment. The main modifications are as follows:
The experiment data of K5A hydrogen engine was under 100% load without EGR. The atmospheric pressure was 101.08 kPa, and initial air temperature is 304 K. The engine intake air temperature was 305.2 K, and the cooling water temperature was 348 K. The intake air humidity was 22.52 g/kg, and the relative humidity of intake air was 78.7%. Moreover, the gas used in the experiment contains 99.8% hydrogen and 0.2% other gases (N2, CH4, CO, H2O etc.). CFD model uses the same initial condition settings as the experiment data.
Point 4: Figure 3: It seems unusual for the cases of 30 º. Why the value was higher than 0 for heat release rates after 20º CA? How about the engine load?
Why the authors choose the cases of 30 º where the position in crank angle of the peak in-cylinder pressure was before TDC? This situation will not happen in the process of engine calibration.
Response 4: Yes, a very good comment. We deleted the cases of 30º, and fixed Figure 3 and Figure 4. This situation really will not happen in the process of engine calibration. The main modifications are as follows:
Figure 3. Pressure and heat release rate under different ignition advance angles.
(a) (b)
Figure 4. Average temperature and NO production rate at different ignition advance angles: (a) Average temperature; (b) NO generation rate.
Thank you very much for the excellent and professional revision of our manuscript.
Yours sincerely,
Hao Guo
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
line 165 what is meant by valve life (=valve lift?)
Line 206 what ist meant with "...and the mixture gas is formed sufficiently after spark". do you mean "... the mixture gas is combusted sufficiently after spark.
Line 380: a hint would be helpful, that the pre-ignition is only a single working cycle and not a avaraged, like which ist typically calculated. after the preignition cycle the next working cycle ist typically very different at a real engine.
Author Response
Response to Reviewer 1 Comments
Dear Reviewer,
Thank you very much for your comments. The manuscript is entitled as follows: “A Numerical Investigation on Abnormal Combustion on a Hydrogen Engine with EGR System
” (Manuscript ID: processes-932239). We also wish to take this opportunity to thank the reviewers for their constructive comments and valuable recommendations. We have carefully revised the manuscript according to reviewers’ suggestion.
Our responses to the comments are listed below:
Point 1: line 165 what is meant by valve life (=valve lift?)
Line 206 what ist meant with "...and the mixture gas is formed sufficiently after spark". do you mean "... the mixture gas is combusted sufficiently after spark.
Response 1: Yes, we fixed this.
Point 2: Line 380: a hint would be helpful, that the pre-ignition is only a single working cycle and not a avaraged, like which ist typically calculated. after the preignition cycle the next working cycle ist typically very different at a real engine.
Response 2: A very good and helpful comment. The main modifications are as follows:
The pre-ignition here is only a single working cycle and not an averaged simulation case, as it is typically calculated. After the pre-ignition cycle, the next working cycle is typically very different at a real engine.
Thank you very much for the excellent and professional revision of our manuscript.
Yours sincerely,
Hao Guo
Author Response File: Author Response.docx
