Spray combustion is commonly employed in propulsion engineering with the most widespread application in internal combustion engines. Numerical simulations of spray combustion are usually performed in the Euler-Lagrange context, where the governing equations of the continuous (carrier) phase are solved in the Eulerian framework, whereas the dispersed phase is modelled by discrete (Lagrange) particles. Some common combustion models for LES, such as flamelet and CMC, rely on the existence of a characteristic variable such as mixture fraction and the strong correlation of the reacting species on this variable. For dilute reacting sprays, the sub-grid mixture fraction conditional scalar dissipation and its PDF are usually modelled by expressions that have been derived and tested for single phase non-premixed combustion. Appropriate modelling for the LES of combustion in relatively dense sprays is less certain since droplet-turbulence-chemistry interactions are not well understood, but may strongly affect the sub-grid quantities. Our scope is to quantify these sub-grid scale interactions and to provide suitable and accurate closures for quantities such as the mixture fraction distribution (i.e. its PDF) and its conditional scalar dissipation for the entire mixture fraction space, ranging from the LES filtered cell mean to the value at the droplet surface. To this end, direct numerical simulations of evaporation and combustion in moderately dense sprays are performed and results are compared to scaling laws for spray combustion.
Movie 1: Fully-resolved DNS of droplet evaporation (and combustion?) in fixed droplet arrays, where a 4x4x3 droplet array is shown. The droplets are indicated by the white circles. The gas phase is coloured by the mixture fraction ranging from zero (grey, pure air) to the maximum mixture fraction value right at the droplet surface (pink, gaseous fuel). The flow is turbulent which leads to transient interactions between the droplet wakes.
Movie 2: Carrier-phase DNS of droplet combustion. The droplets enter the domain from the left side and are shown as grey circles. The gas phase is coloured by the gas temperature. The droplets are heated up by the flame, which triggers droplet evaporation, subsequent fuel vapour/oxidiser mixing, ignition and combustion
- W. Qian, X. Hui, B. Wang, A. Kronenburg, C.-J. Sung, and Y. Lin, “An investigation into oxidation-induced fragmentation of soot aggregates by Langevin dynamics simulations,” Fuel, vol. 334, p. 126547, (2023).
- M. Sontheimer, A. Kronenburg, and O. T. Stein, “Grid dependence of evaporation rates in Euler–Lagrange simulations of dilute sprays,” Combust. Flame, vol. 232, p. 111515, (2021).
- B. Wang, A. Kronenburg, and O. T. Stein, “Modelling sub-grid passive scalar statistics in moderately dense evaporating sprays,” Flow, Turbul. Combust., vol. 103, pp. 519–535, (2019).
- B. Wang, A. Kronenburg, and O. T. Stein, “A new perspective on modelling passive scalar conditional mixing statistics in turbulent spray flames,” Combust. Flame, vol. 208, pp. 376–387, (2019).
- B. Wang, A. Kronenburg, G. L. Tufano, and O. T. Stein, “Fully resolved DNS of droplet array combustion in turbulent convective flows and modelling for mixing fields in inter-droplet space,” Combust. Flame, vol. 189, pp. 347–366, (2018).
- B. Wang, H. Chu, A. Kronenburg, and O. T. Stein, “A Resolved Simulation Study on the Interactions Between Droplets and Turbulent Flames Using OpenFOAM,” in High Performance Computing in Science and Engineering ’17, (2018), pp. 205–220.
- B. Wang, A. Kronenburg, D. Dietzel, and O. T. Stein, “Assessment of scaling laws for mixing fields in inter-droplet space,” Proc. Combust. Inst., vol. 36, pp. 2451–2458, (2017).
- B. Wang, A. Kronenburg, and O. T. Stein, “Assessment of scaling laws for mixing fields in interdroplet space in reacting flows,” in 27th Europ Conf. on Liquid Atomiz. Spray Syst. (ILASS), Brighton, UK, (2016).
- M. R. G. Zoby, A. Kronenburg, S. Navarro-Martinez, and A. J. Marquis, “Assessment of Conventional Droplet Evaporation Models for Spray Flames,” in High Performance Computing in Science and Engineering ’11, (2012), pp. 209–227.
- M. R. G. Zoby, S. Navarro-Martinez, A. Kronenburg, and A. J. Marquis, “Evaporation rates of droplet arrays in turbulent reacting flows,” Proc. Combust. Inst., vol. 33, pp. 2117–2125, (2011).
- M. R. G. Zoby, S. Navarro-Martinez, A. Kronenburg, and A. J. Marquis, “Turbulent mixing in three-dimensional droplet arrays,” Int. J. Heat Fluid Flow, vol. 32, pp. 499–509, (2011).
Andreas KronenburgUniv.-Prof. Dr.
Director of the Institute