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The article presents the results of experimental studies of the collisions characteristics for water droplets in an aerosol at its entry into the air counter flow. The temperature of the latter ranged from 20?C to 500?C. Experiments were also carried out with the flow of combustion products having a temperature of 800- 850?C. The initial dimensions (radii) of the droplets in the aerosol were 50-1000 ?m. Visualization of the droplet motion in the counter flow of air and combustion products required the use of a hollow cylinder made of quartz glass with a height of 1 m and an internal diameter of 0.15 m, a cross-correlation complex and optical methods (particle image velocimetry, particle tracking velocimetry, interferometric particle imaging). The characteristics of the droplet interaction (size, velocity, total surface area of the liquid before and after) were controlled using a high-speed video camera and tracking algorithms in the TEMA AUTOMOTIVE software package. The main modes of drops interaction have been identified: bounce, coagulation, scatter, and breakup. The statistical information database has been obtained to describe the interaction modes using diagrams, taking into account the ratio of the sizes of colliding drops, velocities of their motion, and an angle between trajectories of motion. The influence of gas temperature on the probabilistic criteria of droplet collisions, as well as the integral criterion characterizing the change in the liquid surface area due to the intensification of droplet collisions in the gas medium has been established.

The paper presents the experimental results about fire extinction in the model fire sites of forest combustible materials. We use the high-speed video recording tools during the experiments, as well as the system of multiphase media diagnostics based on panoramic optical flow visualization techniques. The presented experi¬ments prove that it is possible to extinguish the forest combustible material (FCM) by small amount of water. The study considers several ways to stop FCM thermal decomposition: by individual large water droplets (1-3 mm), by an aerosol flow (the droplet size is from 0.05 mm to 0.12 mm), or through water film formation on the FCM surface. Typical durations of the FCM thermal decomposition and time of fire suppression are determined for various conditions of interaction with water. The experimental results identify which amount of water is enough to extinguish the FCM by different ways of water transfer to the reacting surface layer. Fur¬thermore, it is estimated how the component composition and the properties of the tested FCM mixtures effects onto the characteristics of the investigated processes. The residual fraction of the FCM was evaluated by comparison of initial and final (after extinguishing) mass of the sample.

Numerical researches have been carried out to study the influence of air flow temperature and a fossil fuel particle rate on sufficient conditions of ignition in a ?coal particle - air? system. Developed mathematical model takes into account interconnected processes of heat transfer in a coal particle and gas area, thermal decomposition of organic material, diffusion and gas-phase oxidation of volatiles, heating of a coke (carbon) and its heterogeneous ignition. The effect of low-temperature (about 600 K) ignition for a single coal particle is impossible even at variation of its rate (radius) from 0.05 mm to 0.5 mm. Nevertheless this process is possible for group of particles (two, three, et al.) situated at close-range from each other. The physical aspects of the problem are discussed.