High pressure injection systems have essential roles in realizing highly controllable fuel injections in internal combustion engines. The primary atomization processes in the near field of the spray, and even inside the injector, determine the subsequent spray development with a considerable impact on the combustion and pollutant formation. Therefore, the processes should be understood as much as possible; for instance, to develop mathematical and numerical models. However, the experimental difficulties are extremely high, especially near the injector nozzle or inside the nozzle, due to the very small geometrical scales, the highly concentrated optical dense spray processes and the high speed and drastic transient nature of the spray. In this study, several unique and partly recently developed techniques are applied for detailed measurements on the flow inside the nozzle and the spray development very near the nozzle. As far as possible, the same three-hole injector for high pressure diesel injection is used to utilize and compare different measurement approaches. In a comprehensive section, the approach is taken to discuss the measurement results in comparison. It is possible to combine the observations within and outside the injector and to discuss the entire spray development processes for high pressure diesel sprays. This allows one to confirm theories and to provide detailed and, in parts, even quantitative data for the validation of numerical models.
Air assisted atomizers are widely used for various purposes, for example coating processes, medical processes, and sprinkler. However, the spray development processes, especially the breakup phenomena are not fully understood yet. Generally, the main breakup of the air assisted atomizer depends on whether the mixing is internal or external. The border between these processes is not clear. In order to study changes in the spray configuration due to the way of mixing, the spray was investigated for the transition from internal to external mixing. Therefore, an air assisted atomizer which allows adjusting the distance between injector to cover was used. The atomizer consists of two components, which are a liquid injector and an injector cover with orifice. The atomization air flows through the gap between the injector and the cover. The position of cover orifice is able to be traversed from the position fully attached to the injector to several millimetre distances from the injector nozzle. In this study, the water spray characteristics depending on the air and liquid mixture position were investigated experimentally by two optical measurement techniques. Imaging techniques were used for taking the spray structure as well as liquid core in near nozzle field. The water mass flow, atomization air mass flow, and the cover position were changed and their effects on the spray were investigated. Phase Doppler Anemometer (PDA) was applied for measurement of velocity and size of droplets in water spray which injected into the atmosphere. The measurement positions were set at planes which located on 20 and 40mm downstream from the nozzle orifice. For each downstream position, radial profiles of the spray pattern were measured on one air to water flow rate condition. The cover positions were changed and the differences on the droplet velocity and diameter as a function of radial distance on each nozzle cover positions were discussed. Also, high resolution direct imaging technique has been developed and applied for measurement of size of droplets. The results from these measurement techniques were compared and they correspond well at the high air to water flow rate conditions. At the low air to water flow rate condition, the agreement of the results of these measurements became lower. It might be caused by the bouncing unspherical droplets. KeywordsAir-assisted-atomizer, Laser diagnostics, Direct imaging techniques, Atomization process, Atmospheric-pressure IntroductionThe twin fluid atomizer can be applied for various purposes for example coating processes, medical processes, and sprinkler. Most of twin-fluid nozzles were categorized to air assisted or air blast. The main difference is velocity of air flow, and the air velocity of air assisted atomizer is higher than that of air blast atomizer. The effect of mass flow rate of air and water on droplet diameter from air blast atomizer was investigated by Nukiyama etal.[1] in 1939. Lefebvre [2] summarized and explained about factors which influenced to mean droplet size...
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