Project
Modeling of aluminum particle combustion
Aluminum (Al) is the most abundant metal element in the Earth’s crust. With a substantially greater energy density than hydrocarbons, burning aluminum produces solid oxides under standard conditions, which can be easily collected for recycling. Moreover, Al-water reaction yields hydrogen as a valuable byproduct. Despite aluminum’s potential as a promising fuel for the future being widely recognized, the underlying mechanisms are scarcely understood. This proposed research focuses on the commonly encountered heterogeneous combustion of aluminum dust in applications. Recently, several experimental investigations using advanced techniques have shed light on the key characteristics of single aluminum particle combustion. Based on the knowledge gained from the authors’ latest numerical investigations regarding the most crucial issues in modeling the combustion of Al particles within the framework of Eulerian-Lagrangian approach, the primary objective of this proposed research is to develop a reliable Eulerian-Lagrangian modeling framework for predicting existing Al combustion experiments, with the ultimate goal of applying the established framework to realistic applications. Accurate models for convective heat transfer in a transient regime, radiation, melting, evaporation, particle surface reactions, gas-phase reactions, and other key processes need to be developed. For model validation, particle resolved simulations were performed. The detached flame around the burning Al particle and the distinct liquid cap that covers the Al particle were analyzed in detail. This research is part of the Federal Ministry of Education and Research (BMBF)-funded project, the model developed through this research will be used to analyze and optimize a particle reactor designed to produce hydrogen on an industrial scale.
Project Details
Project term
January 21, 2025–January 28, 2026
Affiliations
RWTH Aachen University
Institute
Institute for Combustion Technology (ITV)
Principal Investigator
Methods
Bounary-layer resolved simulations were performed using OpenFOAM for understanding the detailed transport and combustion processes around an Al particle. Eulerin-Lagragian simulations were conducted using CIAO to understand the combustion behavior of Al dust flames that contain multiple particles. The resolved simulations were used as a reference for the development of Lagrangian models. In both solvers, the Navier Stokes equations are solved in the low-Mach limit. CIAO implements a finite difference method on a spatially and temporally staggered grid with the semi-implicit fractional-step method. On the contrary, OpenFOAM allows various temporal discretization schemes and adopts a finite volume method for spatial discretization using a collocated grid. Further, velocity and scalar spatial derivatives are discretized with finite differences scheme in CIAO, while OpenFOAM uses the finite volume-based schemes. Besides, a pressure correction is adopted by both codes to ensure mass conservation. In OpenFOAM, a Pressure-Implicit with Splitting of Operators (PISO) is applied. Both codes decompose the computational domain by applying a distributed memory parallelization strategy using the Message Passing Interface (MPI). A finite rate chemistry approach will be adopted for the combustion modeling.
Results
The resolved simulations have been performed using custom solvers in OpenFOAM for both spherical Al particles and doublet particles with a condensed Al cap. Different Reynolds numbers were studied. The heat and mass transfer and drag force were studied in detail. Particularly, based on the simulation results obtained, a valid Lagrangian modeling method was proposed for Al particle combustion, including new models for the heat and mass transfer and the drag force with and without an oxide cap.
Simulations of aluminum particle dust combustion have been carried out using CIAO. To enable comparison with the experiments, simulations were performed using the AMPAL-637 particle size distribution. A 2D channel configuration has been used. For comparison with experiments, simulations were conducted at different aluminum dust concentrations, ranging from 292 to 598 Good agreements with the experiments in the literature were obtained.
Discussion
The boundary resolved simulations have revealed that the interfacial transport properties of Al droplets are different from those of traditional hydrocarbon droplets. This is particularly the case when an oxide cap, partially covering the Al droplet, is involved. Accordingly, the Lagrangian interfacial models must be revised for representing the distinct feature of burning Al particles. A valid Lagrangian modeling framework has been established. This research has enabled a numerical study of realistic Al dust combustion. The following issues merit further investigation: (1) The condensed fine alumina droplets interact with each other, potentially involving nucleation, surface growth, and coagulation. The detailed size distribution of the alumina droplets is important not only for the combustion but also for the recycling. This needs to be in depth studied. (2) The current Lagrangian modeling framework makes various simplified assumptions, such as the interactions between the discrete alumina droplets, the condensation and deposition onto the surface of Al droplets, interactions between Al particles, etc. These are expected to be considered.
Additional Project Information
DFG classification: 404 Fluid Mechanics, Technical Thermodynamics and Thermal Energy Engineering
Software: CIAO, OpenFOAM
Cluster: CLAIX