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Effects of ambient pressure on ignition and flame characteristics in diesel spray combustion

Pang, Kar Mun; Jangi, Mehdi LU ; Bai, Xue Song LU ; Schramm, Jesper; Walther, Jens Honore and Glarborg, Peter (2019) In Fuel 237. p.676-685
Abstract

This work reports on numerical investigation of effects of ambient pressure (Pam) on spray combustion under engine-like conditions. Three cases with different Pam of 42, 85 and 170 bar at a fixed ambient temperature of 1000 K are considered. Zero-dimensional calculations are first performed for autoignition of stagnant adiabatic homogenous mixtures to evaluate performance of the selected diesel surrogate fuel models and to identify the Pam effects on the most reactive mixture. An Eulerian-based transported probability density function model is then chosen for the three-dimensional computational fluid dynamics study. The results show the predicted ignition delay times and flame lift-off lengths are in... (More)

This work reports on numerical investigation of effects of ambient pressure (Pam) on spray combustion under engine-like conditions. Three cases with different Pam of 42, 85 and 170 bar at a fixed ambient temperature of 1000 K are considered. Zero-dimensional calculations are first performed for autoignition of stagnant adiabatic homogenous mixtures to evaluate performance of the selected diesel surrogate fuel models and to identify the Pam effects on the most reactive mixture. An Eulerian-based transported probability density function model is then chosen for the three-dimensional computational fluid dynamics study. The results show the predicted ignition delay times and flame lift-off lengths are in reasonably good agreement with experiment, with the relative difference below 28%. The current work reveals that low-temperature reactions occur across a wide range of mixture fraction but a noticeable rise of temperature (>100 K above ambient temperature) is detected first on the fuel-lean side of the stoichiometric line in all three cases. The high-temperature ignition occurs first on the fuel-rich side in the 42 and 85 bar cases, where the igniting mixture appears to be more fuel-rich in the latter case. As Pam is further increased to 170 bar, the igniting mixture becomes more fuel-lean and the high-temperature ignition occurs on the fuel-lean side. The ignition behavior is found to depend on both physical and chemical processes. At 170 bar, the reaction rate increases and the associated transition from low- to high-temperature ignition is relatively fast, as compared to the transport of warmer products from the lean zone into the fuel-rich mixture. Also, within the fuel-rich region, the local temperature is low due to liquid fuel vaporization and the condition is not appropriate for ignition. These collectively cause the high-temperature ignition to occur on the fuel-lean side. Analyses on the quasi-steady spray flame structures reveal that, apart from poorer air entrainment due to reduced lift-off length, the higher rich-zone temperature and lower scalar dissipation rate also lead to a higher peak soot volume fraction at higher Pam.

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Please use this url to cite or link to this publication:
author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Ignition, Pressure effects, Spray flame, Transported probability density function
in
Fuel
volume
237
pages
10 pages
publisher
Elsevier
external identifiers
  • scopus:85054672441
ISSN
0016-2361
DOI
10.1016/j.fuel.2018.10.020
language
English
LU publication?
yes
id
1c08bb80-5170-48a0-b0ae-86341a08c559
date added to LUP
2018-10-26 12:44:56
date last changed
2019-09-17 04:42:06
@article{1c08bb80-5170-48a0-b0ae-86341a08c559,
  abstract     = {<p>This work reports on numerical investigation of effects of ambient pressure (P<sub>am</sub>) on spray combustion under engine-like conditions. Three cases with different P<sub>am</sub> of 42, 85 and 170 bar at a fixed ambient temperature of 1000 K are considered. Zero-dimensional calculations are first performed for autoignition of stagnant adiabatic homogenous mixtures to evaluate performance of the selected diesel surrogate fuel models and to identify the P<sub>am</sub> effects on the most reactive mixture. An Eulerian-based transported probability density function model is then chosen for the three-dimensional computational fluid dynamics study. The results show the predicted ignition delay times and flame lift-off lengths are in reasonably good agreement with experiment, with the relative difference below 28%. The current work reveals that low-temperature reactions occur across a wide range of mixture fraction but a noticeable rise of temperature (&gt;100 K above ambient temperature) is detected first on the fuel-lean side of the stoichiometric line in all three cases. The high-temperature ignition occurs first on the fuel-rich side in the 42 and 85 bar cases, where the igniting mixture appears to be more fuel-rich in the latter case. As P<sub>am</sub> is further increased to 170 bar, the igniting mixture becomes more fuel-lean and the high-temperature ignition occurs on the fuel-lean side. The ignition behavior is found to depend on both physical and chemical processes. At 170 bar, the reaction rate increases and the associated transition from low- to high-temperature ignition is relatively fast, as compared to the transport of warmer products from the lean zone into the fuel-rich mixture. Also, within the fuel-rich region, the local temperature is low due to liquid fuel vaporization and the condition is not appropriate for ignition. These collectively cause the high-temperature ignition to occur on the fuel-lean side. Analyses on the quasi-steady spray flame structures reveal that, apart from poorer air entrainment due to reduced lift-off length, the higher rich-zone temperature and lower scalar dissipation rate also lead to a higher peak soot volume fraction at higher P<sub>am</sub>.</p>},
  author       = {Pang, Kar Mun and Jangi, Mehdi and Bai, Xue Song and Schramm, Jesper and Walther, Jens Honore and Glarborg, Peter},
  issn         = {0016-2361},
  keyword      = {Ignition,Pressure effects,Spray flame,Transported probability density function},
  language     = {eng},
  pages        = {676--685},
  publisher    = {Elsevier},
  series       = {Fuel},
  title        = {Effects of ambient pressure on ignition and flame characteristics in diesel spray combustion},
  url          = {http://dx.doi.org/10.1016/j.fuel.2018.10.020},
  volume       = {237},
  year         = {2019},
}