Numerical study of novel OME_1–6 combustion mechanism and spray combustion at changed ambient environments

Abstract

For a climate-neutral future mobility, the so-called e-fuels can play an essential part. Especially, oxygenated e-fuels containing oxygen in their chemical formula have the additional potential to burn with significantly lower soot levels. In particular, polyoxymethylene dimethyl ethers or oxymethylene ethers (PODEs or OMEs) do not contain carbon-carbon bonds, prohibiting the production of soot precursors like acetylene (C₂H₂). These properties make OMEs a highly interesting candidate for future climate-neutral compression-ignition engines. However, to fully leverage their potential, the auto-ignition process, flame propagation, and mixing regimes of the combustion need to be understood. To achieve this, efficient oxidation mechanisms suitable for computational fluid dynamics (CFD) calculations must be developed and validated. The present work aims to highlight the improvements made by developing an adapted oxidation mechanism for OME_1–6 and introducing it into a validated spray combustion CFD model for OMEs. The simulations were conducted for single- and multi-injection patterns, changing ambient temperatures, and oxygen contents. The results were validated against high-pressure and high-temperature constant-pressure chamber experiments. OH*-chemiluminescence measurements accomplished the characterization of the auto-ignition process. Both experiments and simulations were conducted for two different injectors. Significant improvements concerning the prediction of the ignition delay time were accomplished while also retaining an excellent agreement for the flame lift-off length. The spatial zones of high-temperature reaction activity were also affected by the adaption of the reaction kinetics. They showed a greater tendency to form OH* radicals within the center of the spray in accordance with the experiments.

Graphical abstract

Keywords

oxygenated fuels / reaction kinetics / oxidation mechanisms / computational fluid dynamics (CFD) / oxymethylene ethers (OME) / e-fuels / multi-injection / spray-combustion

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Acknowledgements

This work was the scientific result of a research project undertaken by the Research Association for Combustion Engines eV (FVV). The work at the SJTU was funded by the National Key R&D Program of China (Grant No. 2022YFE0209000) and the National Natural Science Foundation of China (Grant No. 52022058). Parts of this work were funded by the Federal Ministry for Economic Affairs and Energy (BMWi) through the German Federation of Industrial Research Associations eV (AiF). The work at the TU Wien was funded by the Ministry for Transport, Innovation and Technology (BMVIT) through the Austrian Research Promotion Agency (FFG, Grant No. 874418). The research was conducted in the framework of the collective research networking program (CORNET) project “eSpray.” The computational results presented were achieved using the Vienna Scientific Cluster (VSC) via the funded project No. 71485.

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Competing interests

The authors declare that they have no conflict of interest.

Notations

Abbreviations
C2H2	Acetylene molecule
CFD	Computational fluid dynamics
CH2O	Formaldehyde molecule
CH3O(−CH2O)n−CH3	Polyoxymethylene dimethyl ether molecule
ECN	Engine Combustion Network
FST	Institute of Fluid System Technology
ID/IDT	Ignition delay timeJSR
KHRT	Kelvin–Helmholtz–Rayleigh–Taylor
LES	Large Eddy Simulation
OH	Hydroxyl radical
OME	Oxymethylene ethers
PODE	Polyoxymethylene dimethyl ethers
OP1	ECN Spray A low temperature conditions (800 K, 22.8 kg/m3, 15% O2)
OP2	ECN Spray A conditions (900 K, 22.8 kg/m3, 15% O2)
OP3	ECN Spray A high temperature conditions (1000 K, 22.8 kg/m3, 15% O2)
OP4	ECN Spray A conditions with multi-injection (900 K, 22.8 kg/m3, 15% O2
OP5	ECN Spray A high oxygen content conditions (900 K, 22.8 kg/m3, 21% O2)
RANS	Reynolds averaged Navier–Stokes equations
SJTU	Shanghai Jiao Tong University
SOC	Start of combustion
SOI	Start of injection
Variables
CA	Injector nozzle hole area contraction coefficient
d	Diameter
k	Pre-exponential factor of reaction
L	Length
\dot{m}	Mass flow
p	Pressure
r/R	Radius
S	Sensitivity coefficient
t	Time
T	Temperature
x	Distance
Z	Mixture fraction
Zi	Element mass fraction
\rho	Density
\tau	Ignition delay time
\varphi	Equivalence ratio
{\varphi }_{\mathrm{\Omega }}	Oxygen equivalence ratio
\mathrm{\Omega }	Oxygen ratio

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2024 The authors (2024). This article is published with open access at link. springer.com and journal.hep.com.cn