In the present work, the combustion of vitiated hydrogen jets issuing from differently shaped nozzles is modelled using the LES method. We investigate the impact of nozzle cross-sectional geometries (circular, square, triangular, hexagonal and hexagram) and the jet Reynolds numbers ($\mathrm{Re}=$ 18,000, 20,000 and 23,600) on the flame lift-off height, its structure, the locations of the temperature maxima and species distributions. The triangular nozzle yields the highest mixing rate and therefore the fastest decay of axial velocity and the fastest growth of the average temperature along the flame axis. It was found that for the largest $\mathrm{Re}$, the zone of intense mixing and the reaction zone occur in distinct regions, while for the lower $\mathrm{Re}$, these regions combine into an indistinguishable zone. Finally, it is shown that the lift-off height of the flames and the mean temperature field are non-linearly correlated with $\mathrm{Re}$ and strongly dependent on the nozzle shape.

In the current work, the jet spray flame reflecting an experimental configuration of a piloted spray burner with a vitiated hot co-flow is modeled using large eddy simulation (LES). We consider a diluted polydisperse spray, which evaporates and diffuses from a fuel-rich spray core, mixes with an oxidizer and eventually auto-ignites. The objective of the present study is to assess an influence of evaporation models and mean droplet diameter on the combustion process in a lifted flame, starting from an auto-ignition up to the flame stabilization. Three evaporation models are involved, i.e., (i) “D² law”, (ii) infinite conductivity model with Stefan flow effect, and (iii) infinite conductivity non-equilibrium evaporation model based on a Langmuir-Knudsen law. An in-house high-order numerical code was used to carry out the computations. The continuous gas phase is modeled in the Eulerian coordinate system while the spray droplets are tracked in space in the Lagrangian manner. The obtained results show that in a stable combustion regime a flame size and liftoff height only slightly depend on evaporation model. However, in general, it is observed that the spray size can affect the flame structure to a much larger extent. On the other hand, for bigger droplets differences in initial size distribution cause only small flame movement downstream or upstream toward the fuel nozzle. For auto-ignition and initial flame development phase it is observed that both the droplets size and evaporation model affect the obtained results significantly.

In the current work the jet spray combustion reflecting an experimental piloted spray burner is simulated numerically. In the simulations the diluted ethanol spray evaporates in the hot surrounding, the gaseous fuel diffuses from spray fuel-rich core into the oxidizer fuel-lean region and autoignites. An in-house high-order compact difference LES solver is used to carry out the computations. The reaction rates are modelled using Implicit LES approach based on the single-step global reaction. The continuous phase is modelled in the Eulerian reference frame while the droplets in the Lagrangian form. The studies are focused on the influence of the co-flow temperature and spray initial Sauter mean diameter (SMD) on the flame lift-off height, autoignition delay and the reaction zone features. The results are compared with the experimental data and show good agreement in terms of lift-off height. It is almost linearly related to the co-flow temperatures. It is found that for the same fuel mass loading, droplets with smaller SMDs significantly shorten the autoignition delay. Moreover the autoignition delay and the lift-off heights are influenced mostly by the droplets SMD rather than by the co-flow temperature.