Application Study Of The Cold Shock Wave Fire-extinguishing System

Fire caused numerous casualties and enormous economic losses every year. In order to prevent fire and reduce the losses, a wide variety of fire-fighting equipments and detection instruments emerge as the times require. But when faced with the fire of tall buildings, forests, grasslands and other special conditions, fire protection supplies and fire fighters could not arrive at fire site in time owing to the limit of terrain, environmental factors and the devices, which resulted in more serious losses. Fire-extinguishing bomb, which could be launched by mortar, missile and other facility, has the advantages of realization remote fire controlling and fire fighting as not subjected to the influence of topography and terrain. But the high cost, poor stability and low security limited its practical application, and mortar, rocket and other launcher devices exsited low accuracy for super high-rise building fire, which did not meet the requirements of fire fighting. Researches mainly focused on structure optimization, fuse design, extinguishing efficiency and related factors, but the mechanism of fire extinction has not been reported.A new unmanned aerial vehicles(UAV) cold shock wave fire-extinguishing system based on fire-extinguishing bomb, FAE, shock wave fire extinction technology and UAV technology was put forward. In the system, UAV was controlled by artificial intelligence to deliver or launch cold shock wave fire-extinguishing bomb at the specified position. Once arrived at the fire site, fuse ignited the bomb, which realized the purpose of fire controlling and fire fighting. Ordinary air shock wave has the characteristics of high temperature and high pressure, while the temperature of shock wave in extinguishing medium was low because of the higher specific heat of the extinguishing medium, which is why named cold shock wave fire-extinguishing system.According to the application process of the UAV cold shock wave fire extinguishing system, the mechanical models of water-based and powder-based fire extinguishing mediums were studied, the inside wall pressure of the fire-extinguishing bomb was tested, air turbulence after the blasting dispersion of extinguishing medium was analyzed, static fire suppression mechanism of cold shock wave fire extinguishing bomb and relative influence factors were researched, the choice of ignition composition and the design of cartridge structure were analyzed. The concrete work of the doctoral dissertation as follows: The mechanical models of water-based and powder-based fire extinguishing mediumThe mechanical models of the water-based fire extinguishing medium were introduced briefly. Stress-strain curves of loose powder were obtained by MTS under uniaxial compression at various loading rates. Combined with SEM picture, we found that a large number of voids existed in the powder medium, compressive strength of the powder increased as the increase of loading stress and loading speed, the powder consumed plenty of energy during the compression process. In order to increase the loading rate of projectile body and reduce the loss of explosion energy, pre-compression powder was put forward. Static and dynamic compressive deformation behaviors of the pre-compression powder at5MPa,10MPa,15Mpa were tested by MTS and SHPB. Found that the yield strength of pre-compression powder increased with the increase of pre-loading and strain rate. Finally, the constitutive model of loose powder and pre-compression powder were establishedThe inside wall pressure test of cold shock wave fire-extinguishing bombFirstly, the relations of the inside wall pressure of the cold shock wave fire extinguishing bomb with projectile body diameter and the center charge weight were studied by dimensional analysis. Then the inside wall pressure of cold shock wave fire-extinguishing bomb filled with loose powder in different inner diameter and charge weight were tested by PVDF pressure sensor. Contrasting to water-based extinguishing bomb, the dispersion charge weight and specific charge of powder-based extinguishing bomb were higher than water-based in order to achieve the same shell fragmentation effects. Contrasting to tested pressure of infinite powder medium, Powder-based medium reflection overpressure at wall is7.8times of incident overpressure. According to the pressure wave tested by experiments, the shell fragmentation of the powder-based extinguishing bomb was resulted from shock wave and blasting gas.The shell fragmentation of cold-shock fire-extinguishing bombJudging from PVC static and dynamic mechanical test results, PVC was visco-plastic material, which had strain strengthening characteristics at initial yield stage and appeared softening when strain value accessed0.032. On the basis of these results and assumptions, a Johnson-Cook constitutive model of PVC, which is coupled with strain injury model, was established. According to the measured pressure, the dynamic response of shell structure was analyzed and the expansion velocity and expansion displacement were solved. Finally shell fragment was studied by experiment and numerical simulation. Found that the shell fragmentation started from outside surface. The shape and size of shell fragments were determined by the quantity of pre-crack, the more pre-cracks, the more uniform the spalls, but the more pre-cracks consumed the more explosive energy. In order to reach the same shell fragmentation effect, the specific charge of water-based extinguishing bomb was lower than powder-based, and the specific charge of loosen powder-based extinguishing bomb was higher than dense powder-based.The dispersion of cold shock wave fire-extinguishing bombFirstly, the blasting dispersion regularity of water-based and powder-based extinguishing bomb were observed by high-speed photography. Then, air turbulence resulted from high speed moving of droplets and powder particles in gas were stimulated by using DPM and two-phase flow model. Finally, the explosive dispersion laws of different extinguishing mediums under small size were obtained by High-Speed Schlieren Method. Found that no matter water-based or powder-based medium, entrainment phenomenon induced by drag force could drive the above flame and plenty of fresh air into the extinguishing medium area, which accelerated the medium suppression velocity and fire temperature descending speed.Suppression mechanism of the cold Shock wave fire-extinguishing bombShock wave formed by explosion dispersion of different extinguishing mediums was observed by schlieren experiment apparatus, found that shock wave with the speed of440m/s were observed in powder-based extinguishing media, while not observed in water-based media. Then, pressure, velocity, density and temperature in front and bacd of shock wave were analyzed by shock wave theory, which demonstrated the feasibility of shock wave suppression. The weak wave motion rule and its affects to surroundings were studied by numerical simulation and experimental analysis. Found that mach reflection that appeared above the liquid surface could speed up the velocity the combustible gas, but the effect was weaker than the acceleration induced by medium explosion dispersion. Afterwards water-based and powder-based suppression mechanisms were introduced briefly, the interaction and extinguishing mechanism between shock wave and media were analyzed detailed. At last, a definition of an influence factor (the height of grenade/flame height) was made. The bomb could not quench oil basin fire when the impact factor below0.118. With the increase of specific charge, the shock became stronger, spray effect and water suppression effects both got better, but strong shock wave could lead to the oil going far away from the fire extinguishing medium area, which caused the fire re-burning and spreadThe application research of the cold shock wave fire-extinguishing bombThe relations among propellant selection, amount and launched speed of cold shock wave fire-extinguishing bomb were studied simply under experiment situation. According to the conservation of energy, the energy efficiency of homemade launch tube was calculated. The different structures of cylindrical shells were designed, found that the shell adding nylon buffer could not break at the launching process.