We study experimentally the isoviscous displacement flow of two immiscible Newtonian fluids in an inclined pipe. The less dense displacing fluid is placed above the denser displaced fluid in a density-stable configuration. The displacing and displaced solutions are oil-and water-based, respectively. The former exhibits nonwetting behavior in the vicinity of the pipe wall, whereas the latter is wetting. The pipe has a small diameter-to-length ratio. The mixing and interpenetration of two fluids have been studied over a wide range of controlling parameters, revealing remarkable results. Compared to the previously studied miscible limit, we observe behavior at the interface between the two fluids where the displaced fluid stays "pinned" to the lower wall of the pipe upon pumping the displacing one. This phenomenon, which is observed over the full range of investigated flow rates, tilt angles, and density contrasts, is associated with the wetting characteristic of the displacing liquid and is also present when light and heavy viscosity mineral oils are used as the displacing fluid. Ultrasonic Doppler velocimetry revealed a segmented velocity profile at the interface of the immiscible fluids. Due to pinning, the efficiency of the removal of displaced fluid in the immiscible limit can be lowered by 14% compared to the miscible case due to the combined effects of the density-stable configuration and the immiscibility of the flow. Within the family of immiscible fluids, the maximum efficiency is achieved at close-to-vertical tilt angles, large density contrasts, and counterintuitively low imposed flow rates, which is of great importance in industrial design.
The results of a three-year collaborative research study into the sources of unburnt hydrocarbon (uHC) emissions are reported. The study sought to extend existing knowledge of the sources in an engine to the crucial period following a cold start and before the-exhaust catalyst becomes fully efective. The study, carried out on a range of engines but centred on the Rover M I 6 four-valve engine, identifed a number of sources, all of which are equally important in the warm-up period. The paper concludes with some recommendations for the control of uHC emissions
NOTATION
AArrhenius factor [(m3/kg)0.6/s] E activation energy (kJ/kg mol) P pressure (kN/m2) R specific gas constant (kJ/kg K) R universal gas constant (kJ/kg mol K)
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