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LES/TPDF investigation of the effects of ambient methanol concentration on pilot fuel ignition characteristics and reaction front structures

Xu, Shijie LU orcid ; Pang, Kar Mun ; Li, Yaopeng LU ; Hadadpour, Ahmad LU ; Yu, Senbin LU ; Zhong, Shenghui LU ; Jangi, Mehdi LU and Bai, Xue song LU (2021) In Fuel 287.
Abstract

Large-eddy simulations with a transported probability density function model coupled with a finite-rate chemistry is applied to study the ignition process of an n-heptane spray in a constant volume chamber with a premixed methanol-air atmosphere under conditions relevant to reactivity controlled compression ignition (RCCI) engines. Three reacting spray cases with initial methanol-air equivalence ratio (ϕm) ranging from 0 to 0.3 are investigated at an initial temperature of 900 K. The case setup is based on the Engine Combustion Network Spray-H configuration, where n-heptane fuel is used. The effects of the ambient methanol-air equivalence ratio on the ignition characteristics and the reaction front structures in... (More)

Large-eddy simulations with a transported probability density function model coupled with a finite-rate chemistry is applied to study the ignition process of an n-heptane spray in a constant volume chamber with a premixed methanol-air atmosphere under conditions relevant to reactivity controlled compression ignition (RCCI) engines. Three reacting spray cases with initial methanol-air equivalence ratio (ϕm) ranging from 0 to 0.3 are investigated at an initial temperature of 900 K. The case setup is based on the Engine Combustion Network Spray-H configuration, where n-heptane fuel is used. The effects of the ambient methanol-air equivalence ratio on the ignition characteristics and the reaction front structures in n-heptane/methanol RCCI combustion are studied in detail. It is found that the ambient methanol affects the low temperature chemistry of n-heptane, which results in a change of spatial distribution of key species such as heptyl-peroxide, and therefore the cool flame structure. With the presence of methanol in the ambient mixture cool flame is found in the entire fuel-rich region of the n-heptane jet, while when methanol is absent in the ambient mixture, the cool flame is established only around the stoichiometric mixture close to the n-heptane injector nozzle. In general, both low- and high-temperature ignition stages of n-heptane ignition are retarded by the methanol chemistry. An increase in ϕm leads to a decrease of the peak heat release rate of the n-heptane first-stage ignition. The chemistry of methanol inhibits the n-heptane ignition by decreasing the overall hydroxyl radicals (OH) formation rate and reducing the OH concentration during the transition period from the first-stage ignition to the second-stage ignition. As a result, the transition time between the two ignition stages is prolonged. Under the present lean methanol/air ambient mixture conditions, the impact of methanol on n-heptane ignition has a tendency of reducing the high-temperature, fuel-rich region, which is in favor of soot reduction.

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author
; ; ; ; ; ; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Auto-ignition, Dual-fuel combustion, Engine Combustion Network, Eulerian stochastic field, Large eddy simulation
in
Fuel
volume
287
article number
119502
publisher
Elsevier
external identifiers
  • scopus:85094918521
ISSN
0016-2361
DOI
10.1016/j.fuel.2020.119502
language
English
LU publication?
yes
id
5c69f74a-b05d-43af-99a7-21368ddec57e
date added to LUP
2020-11-23 10:46:37
date last changed
2022-04-26 21:59:55
@article{5c69f74a-b05d-43af-99a7-21368ddec57e,
  abstract     = {{<p>Large-eddy simulations with a transported probability density function model coupled with a finite-rate chemistry is applied to study the ignition process of an n-heptane spray in a constant volume chamber with a premixed methanol-air atmosphere under conditions relevant to reactivity controlled compression ignition (RCCI) engines. Three reacting spray cases with initial methanol-air equivalence ratio (ϕ<sub>m</sub>) ranging from 0 to 0.3 are investigated at an initial temperature of 900 K. The case setup is based on the Engine Combustion Network Spray-H configuration, where n-heptane fuel is used. The effects of the ambient methanol-air equivalence ratio on the ignition characteristics and the reaction front structures in n-heptane/methanol RCCI combustion are studied in detail. It is found that the ambient methanol affects the low temperature chemistry of n-heptane, which results in a change of spatial distribution of key species such as heptyl-peroxide, and therefore the cool flame structure. With the presence of methanol in the ambient mixture cool flame is found in the entire fuel-rich region of the n-heptane jet, while when methanol is absent in the ambient mixture, the cool flame is established only around the stoichiometric mixture close to the n-heptane injector nozzle. In general, both low- and high-temperature ignition stages of n-heptane ignition are retarded by the methanol chemistry. An increase in ϕ<sub>m</sub> leads to a decrease of the peak heat release rate of the n-heptane first-stage ignition. The chemistry of methanol inhibits the n-heptane ignition by decreasing the overall hydroxyl radicals (OH) formation rate and reducing the OH concentration during the transition period from the first-stage ignition to the second-stage ignition. As a result, the transition time between the two ignition stages is prolonged. Under the present lean methanol/air ambient mixture conditions, the impact of methanol on n-heptane ignition has a tendency of reducing the high-temperature, fuel-rich region, which is in favor of soot reduction.</p>}},
  author       = {{Xu, Shijie and Pang, Kar Mun and Li, Yaopeng and Hadadpour, Ahmad and Yu, Senbin and Zhong, Shenghui and Jangi, Mehdi and Bai, Xue song}},
  issn         = {{0016-2361}},
  keywords     = {{Auto-ignition; Dual-fuel combustion; Engine Combustion Network; Eulerian stochastic field; Large eddy simulation}},
  language     = {{eng}},
  month        = {{03}},
  publisher    = {{Elsevier}},
  series       = {{Fuel}},
  title        = {{LES/TPDF investigation of the effects of ambient methanol concentration on pilot fuel ignition characteristics and reaction front structures}},
  url          = {{http://dx.doi.org/10.1016/j.fuel.2020.119502}},
  doi          = {{10.1016/j.fuel.2020.119502}},
  volume       = {{287}},
  year         = {{2021}},
}