Numerical Study of the Influence of Turbulence–Chemistry Interaction on URANS Simulations of Diesel Spray Flame Structures under Marine Engine-like Conditions
2021
Ong, Jiun Cai | Pang, Kar Mun | Jangi, Mehdi | Bai, Xue-Song | Walther, Jens Honore
The present work performs unsteady Reynolds-averaged Navier–Stokes simulations to study the effect of turbulence–chemistry interaction (TCI) on diesel spray flames. Three nozzle diameters (d₀) of 100, 180, and 363 μm are considered in the present study. The Eulerian stochastic fields (ESF) method (with the TCI effect) and well-stirred reactor (WSR) model (without the TCI effect) are considered in the present work. The model evaluation is carried out for ambient gas densities (ρₐₘ) of 30.0 and 58.5 kg/m³. The ESF method is demonstrated to be able to reproduce the ignition delay time (IDT) and lift-off length (LOL) with an improved accuracy than that from the WSR method. Furthermore, TCI has relatively more influence on LOL than on IDT. A normalized LOL (LOL*) is introduced, which considers the effect of d₀, and its subsequent effect on the fuel-richness in the rich premixed core region is analyzed. The RO₂ distribution is less influenced by the TCI effect as ambient density increases. The ESF model generally predicts a longer and wider CH₂O distribution. The difference in the spatial distribution of CH₂O between the ESF and WSR model diminishes as d₀ increases. At ρₐₘ = 30.0 kg/m³, the ESF method results in a broader region of OH with lower peak OH values than in the WSR case. However, at ρₐₘ = 58.5 kg/m³, the variation of the peak OH value is less susceptible to the increase in d₀ and the presence of the TCI model. Furthermore, the influence of TCI on the total OH mass decreases as d₀ increases. The total NOx mass qualitatively follows the same trend as the total OH mass. This present work clearly shows that the influence of TCI on the global spray and combustion characteristics becomes less prominent when d₀ increases.
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