High-Speed Study of Drop-Weight Impact Ignition of PBX 9501 Using Infrared Thermography

Reaction in explosive materials does not occur as a result of homogenous heating of the sample, but rather from a localized region of high temperature called a hot spot. Observation of hot spot development is critical in understanding the heat transfer mechanisms occurring during reaction. Due to the strong temperature dependence of explosives, the overall reaction rate is dominated physically by these hot spots. Once formed, these hot spots either fail to react chemically due to thermal diffusion or react exothermically thus creating an ignition site in the solid explosive. The slightest difference of physical properties can change the positioning of hot spot development, creating an argument that the differences in material properties influence the formation of hot spots, which produce an exothermic reaction.

Flame Propagation in Natural Gas Fueled Direct Injection Engines

Injected natural gas requires some form of ignition assist in order to ignite in the time available in a diesel engine combustion chamber. A glow plug — a heated surface — is one form of ignition assist. Ignition by glow plug results in a single site of ignition from which the flame must propagate to other jets in the injection pattern. The goal of this work was to determine what factors affect how the flame propagates from this initial ignition site to the remaining unburned mixture site. The combustion of natural gas jets under diesel engine conditions was studied over a range to temperatures, pressures with and without a glow plug shield using a CFR engine as a rapid compression device. The results showed that of all the factors considered it is the geometry of the injection pattern, combustion chamber and glow plug shield that are most dominant in controlling combustion rates and fuel utilization.

Tinnitus

Chronic idiopathic subjective tinnitus is a common condition affecting around one in ten of the population at any given time. For the majority of people it is an annoyance rather than a major health issue but for approximately 0.5 per cent of the population tinnitus interferes with their ability to pursue a normal life. Modern theories of the pathogenesis of the condition concentrate on the central auditory system although the peripheral auditory system can be a trigger or ignition site for tinnitus. Although a cure remains elusive there are several good treatment strategies based on psychological and neurophysiological models of tinnitus that promote habituation to the symptom.

The flame behaviour of liquefied petroleum gas spray impinging on a flat plate in a constant volume combustion chamber

Liquefied petroleum gas (LPG) sprays and diffusion flames are investigated in a constant volume combustion chamber having an impingement plate. The spray and flame images are visualized and compared with diesel and gasoline images over a wide range of ambient pressure. The high-speed digital camera is used to take the flame images. The injection pressure is generated by a Haskel air-driven pump, and the initial chamber pressure is adjusted by the amount of pumping air. The LPG spray and flame photographs are compared with those of gasoline and diesel fuel at the same conditions, and then the spray and flame development behaviour is analysed. The spray photographs show that the dispersion characteristics of LPG spray are sensitive to the ambient pressure. In a low initial chamber pressure LPG fuel in the liquid phase evaporates quickly and does not reach down easily to the impinging plate having a hot coil for ignition. That makes the temperature and equivalence ratio low near the ignition coil, thus making ignition diffcult. On the other hand, in a high initial chamber pressure the spray leaving the nozzle gathers around the ignition site after impinging on the plate, which makes an intense flame near the plate. If applied to small-sized direct injection engines that are not able to avoid spray impinging on a cylinder wall, LPG will have faster and cleaner combustion than diesel or gasoline fuels. However, the chamber geometry should be carefully designed to enable a sufficient amount of vaporized fuel to get to the ignition site