Ignition and combustion characteristics of coal-water-oil slurry placed on modified metal surface at mixed heat transfer

We experimentally determined ignition and combustion of a sessile droplet of coal-water-oil slurry on modified steel samples at mixed heat transfer (radiation, conduction, and convection). The surfaces were modified by two different methods: using abradants and nanosecond laser irradiation. It was shown that a texture of steel samples formed by abradants allows changing the spreading diameter of a 50-mg coal-water-oil slurry droplet (0.44 mm in diameter) from 0.628 mm to 0.743 mm, and, thereby, changing the ignition delay time more than 2 times (from 0.108 s to 0.212 s). A multimodal hierarchical texture formed on steel samples after laser texturing allows increasing the effective contact area of a coal-water-oil slurry droplet with a conductive heat source by more than 18% at identical values of the droplet spreading diameter. This intensifies the droplet heating, increases the formation rate of a combustible vapor-gas mixture, and decreases the ignition delay time by 10-20% (to 0.093 s). A texture formed by laser irradiation increases the number of nucleation centers and intensifies puffing. Modification of steel by nanosecond laser irradiation makes it possible to diminish the intensity of ash deposition on the heating surface after the combustion of coal-water-oil slurry.