One of the topical problems of coal power engineering both from the point of increasing efficiency and ecological safety of heat energy production and need to utilize low-grade coals and coal wastes is the development of combustion technology for coal in the form of a coal-water suspension (CWS). The technologies of CWS combustion place high demands to the spraying devices (nozzles): absence of narrow fuel channels, which can be locked; low fuel velocities relative to the solid walls, which will reduce abrasive wear. The authors of the paper propose a pneumatic nozzle based on the use of the properties of near-wall and cumulative jets of liquid and gas and Coanda effect, which meets the basic requirements for CWS injectors. Aerodynamics control plays the determining role in the efficiency of pneumatic nozzle operation. In this paper, the structure of a single-phase gas flow in the proposed pneumatic nozzle is studied under different regime parameters using the experimental and numerical methods. The studies were carried out using the particle image velocimetry (PIV) and mathematical modeling of the flows by means of the DES and RSM turbulence models. It is shown that in the entire investigated range of excess air pressure, the converging annular jet turns into the concentrated one and forms the direct and return cumulative axial jets in the nozzle near the axis of symmetry. Due to interaction of the return and annular jets in the diffuser, a toroidal vortex is formed. At operation of a liquid fuel nozzle, such a return flow will contribute to the effective destruction of a liquid jet and formation of a highly dispersed two-phase flow. With an excess air pressure in the nozzle of 1 bar, a sound annular converging jet is formed at the nozzle outlet; with a further increase in pressure, the outflowing jet becomes supersonic, the oblique shock waves are formed there, and the axial jet acquires a barrel-like shape with formation of the Mach disks. Such a complex spatial arrangement of the flow (both in the toroidal vortex and outside it) ensures efficient dispersion of liquid fuel in this nozzle.

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The research presents the numerical modeling findings of the secondary breakup of droplets of coal water slurries containing petrochemicals (CWSP). The modeling method of the secondary droplet breakup is based on the VOF method for interface resolution, LES model for describing turbulence, and the technology of adapted dynamic grids. We have established the droplet breakup modes depending on the Weber number varying from 7 to 212. We have also examined the structure of the flow behind droplets. We have tested the numerical method, and the results are in good agreement with the existing experiments.