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

Research output: Contribution to journalArticlepeer-review

Authors

  • Shijie Xu
  • Kar Mun Pang
  • Yaopeng Li
  • Ahmad Hadadpour
  • Senbin Yu
  • Shenghui Zhong
  • Xue song Bai

Colleges, School and Institutes

External organisations

  • Lunds Universitet
  • MAN Energy Solutions
  • Dalian University of Technology
  • Tianjin University

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 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.

Bibliographic note

Funding Information: This work is sponsored by Swedish Research Council (VR), and Swedish Energy Agency through KC–CECOST. Shijie Xu and Shenghui Zhong are sponsored by China Scholarship Council. We thank Rui Li for the assistance on chemical analysis. The simulations are performed on resources provided by the Swedish National Infrastructure for Computing (SNIC) at HPC2N and PDC. Publisher Copyright: © 2020 Elsevier Ltd

Details

Original languageEnglish
Article number119502
Number of pages10
JournalFuel
Volume287
Early online date31 Oct 2020
Publication statusPublished - 1 Mar 2021

Keywords

  • Dual-fuel combustion, Auto-ignition, Engine Combustion Network, Large eddy simulation, Eulerian stochastic field