LES and RANS Spray Combustion Analysis of OME_3-5 and n-Dodecane

Journal Article · Wed May 08 00:00:00 EDT 2024 · Energies

DOI:https://doi.org/10.3390/en17102265· OSTI ID:2589246

Wiesmann, Frederik ^[1]; Nguyen, Tuan M. ^[2]; Manin, Julien ^[2]; Pickett, Lyle M. ^[2]; Wan, Kevin ^[2]; Tagliante, Fabien ^[2]; Lauer, Thomas ^[1]

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1. Technische Univ. Wien (Austria)
2. Sandia National Laboratories (SNL-CA), Livermore, CA (United States)

Clean-burning oxygenated and synthetic fuels derived from renewable power, so-called e-fuels, are a promising pathway to decarbonize compression–ignition engines. Polyoxymethylene dimethyl ethers (PODEs or OMEs) are one candidate of such fuels with good prospects. Their lack of carbon-to-carbon bonds and high concentration of chemically bound oxygen effectively negate the emergence of polycyclic aromatic hydrocarbons (PAHs) and even their precursors like acetylene (C₂H₂), enabling soot-free combustion without the soot-NO_x trade-off common for diesel engines. The differences in the spray combustion process for OMEs and diesel-like reference fuels like n-dodecane and their potential implications on engine applications include discrepancies in the observed ignition delay, the stabilized flame lift-off location, and significant deviations in high-temperature flame morphology. For CFD simulations, the accurate modeling and prediction of these differences between OMEs and n-dodecane proved challenging. This study investigates the spray combustion process of an OME_{3 − 5} mixture and n-dodecane with advanced optical diagnostics, Reynolds-Averaged Navier–Stokes (RANS), and Large-Eddy Simulations (LESs) within a constant-volume vessel. Cool-flame and high-temperature combustion were measured simultaneously via high-speed (50 kHz) imaging with formaldehyde (CH₂O) planar laser-induced fluorescence (PLIF) representing the former and line-of-sight OH* chemiluminescence the latter. Both RANS and LES simulations accurately describe the cool-flame development process with the formation of CH₂O. However, CH₂O consumption and the onset of high-temperature reactions, signaled by the rise of OH* levels, show significant deviations between RANS, LES, and experiments as well as between n-dodecane and OME. A focus is set on the quality of the simulated results compared to the experimentally observed spatial distribution of OH*, especially in OME fuel-rich regions. The influence of the turbulence modeling is investigated for the two distinct ambient temperatures of 900 K and 1200 K within the Engine Combustion Network Spray A setup. The capabilities and limitations of the RANS simulations are demonstrated with the initial cool-flame propagation and periodic oscillations of CH₂O formation/consumption during the quasi-steady combustion period captured by the LES.

• Research Organization: Sandia National Laboratories (SNL-CA), Livermore, CA (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA); USDOE Office of Energy Efficiency and Renewable Energy (EERE), Office of Sustainable Transportation. Vehicle Technologies Office (VTO); Austrian Research Promotion Agency (FFG)
• Grant/Contract Number: NA0003525
• OSTI ID: 2589246
• Journal Information: Energies, Journal Name: Energies Journal Issue: 10 Vol. 17; ISSN 1996-1073
• Publisher: MDPI AG
• Country of Publication: United States
• Language: English

Related Subjects

CFD
ECN
LES
OME
PODE
RANS
e-fuels
oxygenated fuels
polyoxymethylene ether
spray combustion