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Comment on the paper “Experimental study of effect of hydrogen addition on combustion of low caloric value gas fuels”
international journal of hydrogen energy xxx (xxxx) xxx
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/he
Comment on the paper “Experimental study of effect of hydrogen addition on combustion of low caloric value gas fuels” € Parsa Tamadonfar a, Omer L. Gu¨lder b,* a b
Department of Aerospace Engineering, Sharif University of Technology, Tehran, Iran Institute for Aerospace Studies, University of Toronto, Toronto, Canada
article info
abstract
Article history:
This short communication points to some dubious and physically unattainable experi-
Received 3 November 2018
mental data and results reported by Yue et al. [1] on the effect of hydrogen enrichment of
Accepted 3 December 2018
low calorific value gas on engine performance.
Available online xxx
© 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Keywords: Hydrogen enrichment Engine performance Low calorific value gas
In a recent paper in press in this journal by Yue et al. [1], the authors reported experimental data regarding the combustion pressure, engine volumetric efficiency, flame thickness, Markstein length, and the vorticity within the engine when various fractions of hydrogen (and carbon dioxide) were added to the fuel consisting of mainly methane. Although the authors [1] declare that “data from [sic] Figs. 2e8 (of Yue et al. paper [1]) were obtained by experiments”, to our surprise the paper did not include the description of any measurement techniques used nor did it cite references or authors’ previous publications that would have the experimental methodology information. A closer scrutiny of the data presented revealed some disconcerting issues. These are detailed below in the order they appeared in the paper [1]. The combustion pressure profiles with RH2 ¼ 10% and 30% shown in Fig. 2 of Yue et al. paper [1] are puzzling. At the fixed equivalence ratio of unity, engine speed of 1500 rpm at a throttle setting of 30%, the combustion pressure difference
between the two cases would be mainly dependent on the change in the number of moles of the combustion products, and on the combustion temperature to a limited extend. Switching from RH2 ¼ 10% to RH2 ¼ 30%, the ratio of the number of moles of products to the number of moles of reactants for the stoichiometric case will change from 0.995 to 0.982. That is, with more hydrogen addition to the reactants, number of moles of products decrease. Further, increasing RH2 from 10% to 30% would not change the combustion temperature significantly. Under these circumstances, the measured maximum pressure increase of almost a factor of two, when RH2 changes from 10% to 30%, is not justifiable. Even considering the faster burn rate with increasing hydrogen fraction wouldn't explain the pressure increase reported in Fig. 2 of Yue et al. paper [1]. The authors claim that the addition of hydrogen to the low calorific value gas enhances the engine volumetric efficiency. It is not clear how does the hydrogen addition improve the
* Corresponding author. € E-mail addresses: [email protected], [email protected] (O.L. Gu¨lder). https://doi.org/10.1016/j.ijhydene.2018.12.006 0360-3199/© 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. € Comment on the paper “Experimental study of effect of hydrogen addition on Please cite this article as: Tamadonfar P, Gu¨lder OL, combustion of low caloric value gas fuels”, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2018.12.006
2
international journal of hydrogen energy xxx (xxxx) xxx
engine volumetric efficiency. What is the methodology the authors used to assess the engine volumetric efficiency? There is no indication of the methodology used to measure the flame thickness data plotted in Fig. 3a of Yue et al. paper [1]. Common techniques used by researchers to estimate the flame thickness include planar laser-based flame diagnostics such as OH-PLIF and Rayleigh scattering. On the other hand, applying such techniques to flames in the combustion chambers of running engines is not trivial. What was the experimental methodology the authors employed to infer the flame front thickness with various fuel compositions? Similar concerns can be raised for the reported variations of density ratio, Lewis number, and Markstein length with engine crank angle displayed in Figs. 3b, c, and d of Yue et al. paper [1]. What is definition of Markstein length for premixed turbulent flames? What variables of the flame front were measured to get the Markstein length? It is a mystery how had the pictures shown in Fig. 4 of Yue et al. paper [1] been captured. Are they Schlieren images? Are these images from the combustion chamber of the ZS1100 M type single cylinder gas engine mentioned in the paper's experimental section or from a different combustion apparatus? The paper does not mention any suitable experimental set up for such image capture nor the availability of an optically accessible research engine. The authors plotted in Fig. 8a of Yue et al. paper [1] vorticity values as a function of engine crank angle for various fuel compositions. As is well-known, vorticity cannot be measured directly, but can be evaluated from the velocity field data. Formal definition of vorticity can be written as ! w ¼V! u that is, the vorticity is the curl of the velocity vector. This means that velocity field data are essential to get an estimate
of the vorticity. How did the authors measure the velocity field? At what spatial location within the combustion chamber had the vorticity values been evaluated? Fig. 8b displays the variation of the combustion progress variable as a function of engine crank angle. What is the definition of “combustion progress variable”? How did the authors measure it? We are hesitant to suggest that the authors “fabricated” all the data reported in the paper; however all indications paint a picture of a paper based on mostly made-up data. This is a very troubling incident and we were perplexed with the fact that such a manuscript had managed to pass through the assessment of the reviewers of the IJHE which has a relatively high impact factor among energy-related journals. One of us being a reviewer of this journal (OLG), we feel obligated to draw attention of the editors and reviewers to prevent similar incidences that would tarnish the excellent reputation of the IJHE. This paper [1] was brought to our attention as a result of an inappropriate citation of one of our papers (Ref. 10 of Yue et al. paper [1]). The authors referred to our publication as “Tamadonfar [10] used hysteresis method to measure the laminar combustion rate of methane and propane mixed with hydrogen, and found that the laminar combustion rate of the mixture was linear with hydrogen fraction”, which has nothing to do with the subject matter and content of our publication.
reference
[1] Jian Hai Yue, Hang Zhou, Ming Qiang Zhu. Experimental study of effect of hydrogen addition on combustion of low caloric value gas fuels. Int J Hydrogen Energy (in press) https://doi. org/10.1016/j.ijhydene.2018.08.086.
€ Comment on the paper “Experimental study of effect of hydrogen addition on Please cite this article as: Tamadonfar P, Gu¨lder OL, combustion of low caloric value gas fuels”, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2018.12.006
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/he
Comment on the paper “Experimental study of effect of hydrogen addition on combustion of low caloric value gas fuels” € Parsa Tamadonfar a, Omer L. Gu¨lder b,* a b
Department of Aerospace Engineering, Sharif University of Technology, Tehran, Iran Institute for Aerospace Studies, University of Toronto, Toronto, Canada
article info
abstract
Article history:
This short communication points to some dubious and physically unattainable experi-
Received 3 November 2018
mental data and results reported by Yue et al. [1] on the effect of hydrogen enrichment of
Accepted 3 December 2018
low calorific value gas on engine performance.
Available online xxx
© 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Keywords: Hydrogen enrichment Engine performance Low calorific value gas
In a recent paper in press in this journal by Yue et al. [1], the authors reported experimental data regarding the combustion pressure, engine volumetric efficiency, flame thickness, Markstein length, and the vorticity within the engine when various fractions of hydrogen (and carbon dioxide) were added to the fuel consisting of mainly methane. Although the authors [1] declare that “data from [sic] Figs. 2e8 (of Yue et al. paper [1]) were obtained by experiments”, to our surprise the paper did not include the description of any measurement techniques used nor did it cite references or authors’ previous publications that would have the experimental methodology information. A closer scrutiny of the data presented revealed some disconcerting issues. These are detailed below in the order they appeared in the paper [1]. The combustion pressure profiles with RH2 ¼ 10% and 30% shown in Fig. 2 of Yue et al. paper [1] are puzzling. At the fixed equivalence ratio of unity, engine speed of 1500 rpm at a throttle setting of 30%, the combustion pressure difference
between the two cases would be mainly dependent on the change in the number of moles of the combustion products, and on the combustion temperature to a limited extend. Switching from RH2 ¼ 10% to RH2 ¼ 30%, the ratio of the number of moles of products to the number of moles of reactants for the stoichiometric case will change from 0.995 to 0.982. That is, with more hydrogen addition to the reactants, number of moles of products decrease. Further, increasing RH2 from 10% to 30% would not change the combustion temperature significantly. Under these circumstances, the measured maximum pressure increase of almost a factor of two, when RH2 changes from 10% to 30%, is not justifiable. Even considering the faster burn rate with increasing hydrogen fraction wouldn't explain the pressure increase reported in Fig. 2 of Yue et al. paper [1]. The authors claim that the addition of hydrogen to the low calorific value gas enhances the engine volumetric efficiency. It is not clear how does the hydrogen addition improve the
* Corresponding author. € E-mail addresses: [email protected], [email protected] (O.L. Gu¨lder). https://doi.org/10.1016/j.ijhydene.2018.12.006 0360-3199/© 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. € Comment on the paper “Experimental study of effect of hydrogen addition on Please cite this article as: Tamadonfar P, Gu¨lder OL, combustion of low caloric value gas fuels”, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2018.12.006
2
international journal of hydrogen energy xxx (xxxx) xxx
engine volumetric efficiency. What is the methodology the authors used to assess the engine volumetric efficiency? There is no indication of the methodology used to measure the flame thickness data plotted in Fig. 3a of Yue et al. paper [1]. Common techniques used by researchers to estimate the flame thickness include planar laser-based flame diagnostics such as OH-PLIF and Rayleigh scattering. On the other hand, applying such techniques to flames in the combustion chambers of running engines is not trivial. What was the experimental methodology the authors employed to infer the flame front thickness with various fuel compositions? Similar concerns can be raised for the reported variations of density ratio, Lewis number, and Markstein length with engine crank angle displayed in Figs. 3b, c, and d of Yue et al. paper [1]. What is definition of Markstein length for premixed turbulent flames? What variables of the flame front were measured to get the Markstein length? It is a mystery how had the pictures shown in Fig. 4 of Yue et al. paper [1] been captured. Are they Schlieren images? Are these images from the combustion chamber of the ZS1100 M type single cylinder gas engine mentioned in the paper's experimental section or from a different combustion apparatus? The paper does not mention any suitable experimental set up for such image capture nor the availability of an optically accessible research engine. The authors plotted in Fig. 8a of Yue et al. paper [1] vorticity values as a function of engine crank angle for various fuel compositions. As is well-known, vorticity cannot be measured directly, but can be evaluated from the velocity field data. Formal definition of vorticity can be written as ! w ¼V! u that is, the vorticity is the curl of the velocity vector. This means that velocity field data are essential to get an estimate
of the vorticity. How did the authors measure the velocity field? At what spatial location within the combustion chamber had the vorticity values been evaluated? Fig. 8b displays the variation of the combustion progress variable as a function of engine crank angle. What is the definition of “combustion progress variable”? How did the authors measure it? We are hesitant to suggest that the authors “fabricated” all the data reported in the paper; however all indications paint a picture of a paper based on mostly made-up data. This is a very troubling incident and we were perplexed with the fact that such a manuscript had managed to pass through the assessment of the reviewers of the IJHE which has a relatively high impact factor among energy-related journals. One of us being a reviewer of this journal (OLG), we feel obligated to draw attention of the editors and reviewers to prevent similar incidences that would tarnish the excellent reputation of the IJHE. This paper [1] was brought to our attention as a result of an inappropriate citation of one of our papers (Ref. 10 of Yue et al. paper [1]). The authors referred to our publication as “Tamadonfar [10] used hysteresis method to measure the laminar combustion rate of methane and propane mixed with hydrogen, and found that the laminar combustion rate of the mixture was linear with hydrogen fraction”, which has nothing to do with the subject matter and content of our publication.
reference
[1] Jian Hai Yue, Hang Zhou, Ming Qiang Zhu. Experimental study of effect of hydrogen addition on combustion of low caloric value gas fuels. Int J Hydrogen Energy (in press) https://doi. org/10.1016/j.ijhydene.2018.08.086.
€ Comment on the paper “Experimental study of effect of hydrogen addition on Please cite this article as: Tamadonfar P, Gu¨lder OL, combustion of low caloric value gas fuels”, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2018.12.006