A parametric study of ignition dynamics at ECN Spray A thermochemical conditions using 2D DNS

Journal Article · Sat Nov 03 00:00:00 EDT 2018 · Proceedings of the Combustion Institute

DOI:https://doi.org/10.1016/j.proci.2018.08.026· OSTI ID:1497654

Krisman, Alex ^[1]; Hawkes, Evatt R. ^[2]; Chen, Jacqueline H. ^[1]

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1. Sandia National Lab. (SNL-CA), Livermore, CA (United States)
2. The University of New South Wales, Sydney, NSW (Australia)

The ignition process in diesel engines is highly complex and incompletely understood. Here, two-dimensional direct numerical simulations are performed to investigate the ignition dynamics and their sensitivity to thermochemical and mixing parameters. The thermochemical and mixing conditions are matched to the benchmark Spray A experiment from the Engine Combustion Network. The results reveal a complex ignition process with overlapping stages of: low-temperature ignition (cool flames), rich premixed ignition, and nonpremixed ignition, which are qualitatively consistent with prior experimental and numerical investigations, however, this is the first time that fully-resolved simulations have been reported at the actual Spray A thermochemical condition. Parametric variations are then performed for the Damköhler number Da, oxidiser temperature, oxygen concentration, and peak mixture fraction (a measure of premixedness), to study their effect on the ignition dynamics. It is observed that with both increasing oxidiser temperature and decreasing oxygen concentration, that the cool flame moves to richer mixtures, the overlap in the ignition stages decreases, and the (nondimensional) time taken to reach a fully burning state increases. With increasing Da, the cool-flame speed is decreased due to lower mean mixing rates, which causes a delayed onset of high-temperature ignition. With increasing peak mixture fraction, the onset of each stage of ignition is not affected, but the overall duration of the ignition increases leading to a longer burn duration. In conclusion, the results suggest that turbulence–chemistry interactions play a significant role in determining the timing and location in composition space of the entire ignition process.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Oak Ridge Leadership Computing Facility (OLCF); Sandia National Laboratories (SNL-CA), Livermore, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Chemical Sciences, Geosciences & Biosciences Division; USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: AC04-94AL85000; NA0003525; AC05-00OR22725
• OSTI ID: 1497654
• Alternate ID(s): OSTI ID: 1637107
• Report Number(s): SAND--2017-13722J; 672182
• Journal Information: Proceedings of the Combustion Institute, Journal Name: Proceedings of the Combustion Institute Journal Issue: 4 Vol. 37; ISSN 1540-7489
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
42 ENGINEERING
Combustion mode analysis
Negative temperature coefficient
Spray A
Two-stage ignition
n-dodecane