Large-eddy simulation of n-dodecane spray flame: Effects of nozzle diameters on autoignition at varying ambient temperatures

Research output: Contribution to journalArticlepeer-review

Authors

  • Jiun Cai Ong
  • Kar Mun Pang
  • Xue Song Bai
  • Mehdi Jangi
  • Jens Honore Walther

Colleges, School and Institutes

External organisations

  • Technical University of Denmark
  • MAN Energy Solutions
  • Lunds Universitet
  • ETH Zurich

Abstract

In the present study, large-eddy simulations (LES) are used to identify the underlying mechanism that governs the ignition phenomena of spray flames from different nozzle diameters when the ambient temperature (T am) varies. Two nozzle sizes of 90μm and 186μm are chosen. They correspond to the nozzle sizes used by Spray A and Spray D, respectively, in the Engine Combustion Network. LES studies of both nozzles are performed at three T am of 800K, 900K, and 1000K. The numerical models are validated using the experimental liquid and vapor penetration, mixture fraction (Z) distribution, as well as ignition delay time (IDT). The ignition characteristics of both Spray A and Spray D are well predicted, with a maximum relative difference of 14% as compared to the experiments. The simulations also predict the annular ignition sites for Spray D at T am 900K, which is consistent with the experimental observation. It is found that the mixture with Z 0.2 at the spray periphery is more favorable for ignition to occur than the overly fuel-rich mixture of Z < 0.2 formed in the core of spray. This leads to the annular ignition sites at higher T am. Significantly longer IDT for Spray D is obtained at T am of 800K due to higher scalar dissipation rates (χ) during high temperature (HT) ignition. The maximum χ during HT ignition for Spray D is larger than that in Spray A by approximately a factor of 5. In contrast, at Tam=K, the χ values are similar between Spray A and Spray D. This elucidates the increase in the difference of IDT between Spray D and Spray A as T am decreases. This may explain the contradicting findings on the effects of nozzle diameters on IDT from literature.

Bibliographic note

Funding Information: The authors gratefully acknowledge the financial support from the Independent Research Fund Denmark (DFF) and MAN Energy Solutions under the grant number 8022-00143B. The computation was performed using the Niflheim cluster at the Technical University of Denmark (DTU). Publisher Copyright: © 2020 The Combustion Institute. Copyright: Copyright 2020 Elsevier B.V., All rights reserved.

Details

Original languageEnglish
JournalProceedings of the Combustion Institute
Publication statusAccepted/In press - 2020

Keywords

  • Autoignition, LES, Nozzle Size, Spray A, Spray D