In this paper, we conducted an experimental investigation on water droplets gravitating in a layer of typical forest fuel (as illustrated by pine needle litter) in the course of its thermal decomposition. We used a high-speed (200 fps) video recording system, Tema Automotive software with continuous tracking of a moving object as well as a set of low-inertia (no more than 0.1 second) thermocouples. Similar experiments were performed at moderate temperatures (below the onset temperature of forest fuel pyrolysis, i. e. about 300 K). Two approaches were used: continuous tracking of a moving water droplet using high-speed video recording and registration of a droplet path using the readings of thermocouples placed at different levels in a forest fuel layer. We determined the typical depths of an forest fuel layer that water droplets reach with the initial volume of these droplets ranging from 90 to 900 µL. The typical velocities of water droplets were calculated at different depths of the forest fuel layer. We also determined the share of the mass of water spent in an forest fuel layer on evaporation and cooling of the material down to the temperatures below those of thermal decomposition. Finally, we identified the physical processes influencing water droplets moving through the layers of forest fuel heated up to the high temperatures similar to those of thermal decomposition.

This work studies the process feasibility of milling a metal-matrix composite based on Inconel 625 with added NiTi-TiB2 fabricated by direct laser deposition. The composite is intended for manufacturing turbine blades and it has strength characteristics on par with those of Inconel 625. However, the addition of TiB2 has improved its heat and wear resistance. This material is new, and its machinability has not been studied. The new composite was milled with end mill cutters, and recommendations were worked out on the cutting speed, feed per tooth, cutter flank angle, as well as depth and width of milling. The wear of cutter teeth flank was more intense. After the flank wear land on the back surface of a tooth had reached 0.11–0.15 mm, there was a sharp increase in the forces applied which was followed by brittle fracture of the tooth. Milling at a speed of 25 m/min ensured 28 min of stable operation. However, afterwards the critical wear value of 0.11 mm was quickly approached at a cutting speed of 50 m/min, and critical wear followed after 14 min. Dependencies of the cutting forces vs. time for all the selected cutting speeds and throughout the entire testing time period have a tendency to increase, which indicates the influence of cutter wear on the cutting forces. It was found that the durability of the cutters increases with an increase in the milling width and a decrease in the milling depth.

The article presents the results of experimental studies of water droplets propagation through the sample of typical forest fuel materials: needles, leaves, and their mixture. Different conditions are considered: without any additional energy supply, with heating, in the course of intensive thermal decomposition and flaming combustion. Three methods of registration are applied: thermocouple measurements, control of the weight of the sample as a whole and of its individual layers, and high-speed video recording. Water-based compositions with special additives (bentonite, bischofite, and foaming agents) typical for forest fire extinguishing systems are used. The experiments are carried out using aerosol and single water drops, as well as a small group of the latter. It is shown that the mechanisms, conditions and characteristics of droplet propagation through the layers of needles, leaves and their mixtures differ significantly. The scientific novelty of the work is the determining of the values of all the key characteristics of these processes in the conditions of intensive pyrolysis of the material, as well as through its inert layers.

This article presents the main findings of the experimental research into the fire suppression by continuous spraying of water over the combustion zone and by pulsed liquid aerosol delivery according to two schemes. The test samples contained either birch leaves only or mixed of (leaves, twigs, and needles). We monitored the temperature in the fuel bed and used thermocouple readings to determine the conditions and characteristics of suppressing the combustion and thermal decomposition of the material. Using optical methods and high speed recording, we obtained the parameters of sprayed liquid-flow as well as the processes involved in the interaction between liquid aerosol and the decomposing forest fuel. The experimental study helped us establish how much time and quenching liquid is sufficient to suppress the forest fuel combustion. Furthermore, we determined the influence of the forest fuel volume on the conditions and characteristics of the processes under study. Finally, we identified the main physical principles of the thermal decomposition of forest fuel when using the proposed approaches to spraying water into the combustion zone. The research findings enable the optimization of aerial firefighting in terms of wildfire containment and suppression.