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Evaluation and optimisation of phenomenological multi-step soot model for spray combustion under diesel engine-like operating conditions

Pang, Kar Mun; Jangi, Mehdi LU ; Bai, Xue-Song LU and Schramm, Jesper (2015) In Combustion Theory and Modelling 19(3). p.279-308
Abstract
In this work, a two-dimensional computational fluid dynamics study is reported of an n-heptane combustion event and the associated soot formation process in a constant volume combustion chamber. The key interest here is to evaluate the sensitivity of the chemical kinetics and submodels of a semi-empirical soot model in predicting the associated events. Numerical computation is performed using an open-source code and a chemistry coordinate mapping approach is used to expedite the calculation. A library consisting of various phenomenological multi-step soot models is constructed and integrated with the spray combustion solver. Prior to the soot modelling, combustion simulations are carried out. Numerical results show that the ignition delay... (More)
In this work, a two-dimensional computational fluid dynamics study is reported of an n-heptane combustion event and the associated soot formation process in a constant volume combustion chamber. The key interest here is to evaluate the sensitivity of the chemical kinetics and submodels of a semi-empirical soot model in predicting the associated events. Numerical computation is performed using an open-source code and a chemistry coordinate mapping approach is used to expedite the calculation. A library consisting of various phenomenological multi-step soot models is constructed and integrated with the spray combustion solver. Prior to the soot modelling, combustion simulations are carried out. Numerical results show that the ignition delay times and lift-off lengths exhibit good agreement with the experimental measurements across a wide range of operating conditions, apart from those in the cases with ambient temperature lower than 850 K. The variation of the soot precursor production with respect to the change of ambient oxygen levels qualitatively agrees with that of the conceptual models when the skeletal n-heptane mechanism is integrated with a reduced pyrene chemistry. Subsequently, a comprehensive sensitivity analysis is carried out to appraise the existing soot formation and oxidation submodels. It is revealed that the soot formation is captured when the surface growth rate is calculated using a square root function of the soot specific surface area and when a pressure-dependent model constant is considered. An optimised soot model is then proposed based on the knowledge gained through this exercise. With the implementation of optimised model, the simulated soot onset and transport phenomena before reaching quasi-steady state agree reasonably well with the experimental observation. Also, variation of spatial soot distribution and soot mass produced at oxygen molar fractions ranging from 10.0 to 21.0% for both low and high density conditions are reproduced. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
soot oxidation, n-heptane, soot formation, chemical mechanism, diesel
in
Combustion Theory and Modelling
volume
19
issue
3
pages
279 - 308
publisher
Taylor & Francis
external identifiers
  • wos:000354444000001
  • scopus:84929270367
ISSN
1364-7830
DOI
10.1080/13647830.2015.1019929
language
English
LU publication?
yes
id
a325e7d5-a851-4f25-9597-96e25a8ed08e (old id 7432329)
date added to LUP
2015-06-25 12:17:05
date last changed
2017-10-01 03:33:23
@article{a325e7d5-a851-4f25-9597-96e25a8ed08e,
  abstract     = {In this work, a two-dimensional computational fluid dynamics study is reported of an n-heptane combustion event and the associated soot formation process in a constant volume combustion chamber. The key interest here is to evaluate the sensitivity of the chemical kinetics and submodels of a semi-empirical soot model in predicting the associated events. Numerical computation is performed using an open-source code and a chemistry coordinate mapping approach is used to expedite the calculation. A library consisting of various phenomenological multi-step soot models is constructed and integrated with the spray combustion solver. Prior to the soot modelling, combustion simulations are carried out. Numerical results show that the ignition delay times and lift-off lengths exhibit good agreement with the experimental measurements across a wide range of operating conditions, apart from those in the cases with ambient temperature lower than 850 K. The variation of the soot precursor production with respect to the change of ambient oxygen levels qualitatively agrees with that of the conceptual models when the skeletal n-heptane mechanism is integrated with a reduced pyrene chemistry. Subsequently, a comprehensive sensitivity analysis is carried out to appraise the existing soot formation and oxidation submodels. It is revealed that the soot formation is captured when the surface growth rate is calculated using a square root function of the soot specific surface area and when a pressure-dependent model constant is considered. An optimised soot model is then proposed based on the knowledge gained through this exercise. With the implementation of optimised model, the simulated soot onset and transport phenomena before reaching quasi-steady state agree reasonably well with the experimental observation. Also, variation of spatial soot distribution and soot mass produced at oxygen molar fractions ranging from 10.0 to 21.0% for both low and high density conditions are reproduced.},
  author       = {Pang, Kar Mun and Jangi, Mehdi and Bai, Xue-Song and Schramm, Jesper},
  issn         = {1364-7830},
  keyword      = {soot oxidation,n-heptane,soot formation,chemical mechanism,diesel},
  language     = {eng},
  number       = {3},
  pages        = {279--308},
  publisher    = {Taylor & Francis},
  series       = {Combustion Theory and Modelling},
  title        = {Evaluation and optimisation of phenomenological multi-step soot model for spray combustion under diesel engine-like operating conditions},
  url          = {http://dx.doi.org/10.1080/13647830.2015.1019929},
  volume       = {19},
  year         = {2015},
}