The tribology of cam-roller follower conjunction is highly dependent on the engine type and working conditions. The interface experiences transient conditions due to variations in contact geometry and kinematics, as well as loading. These lead to instantaneous and capricious behavior of the lubricant through the contact, which determines the regime of lubrication. The resulting frictional characteristics are affected by the shear of the lubricant film and the interaction of rough surfaces themselves. Thus, specific analysis is required for any intended new engine configuration. Therefore, a tribo-dynamic model, combining valve train dynamics, contact kinematics and tribological analysis is required. An important issue is to develop a simple yet reliable and representative model to address the above mentioned pertinent issues. This would make for rapid scenario-building simulations which are critical in industrial design time-scales. The current model has been developed in response to the above mentioned requirements. A multi-body dynamic model for the valve train system based on the key design parameters is developed and integrated with an EHL tribological model for the cam-follower contact. To keep the model simple and easy to use and to avoid time-consuming computations, the analytical EHL model makes use of Grubin’s oil film thickness equation. Viscous and boundary contributions to friction are obtained as these account for the losses which adversely affect the engine fuel efficiency.
The Darcy–Buckingham (DB) law, critical to the prediction of unsaturated flow, is widely used but has rarely been experimentally tested, and therefore may not be adequate in certain conditions. Failure of this law would imply that the unsaturated hydraulic conductivity is not constant for a given water content, as assumed in nearly all subsurface flow models. This study aims to test the DB law on unsaturated porous rock, complementing the few previous tests, all done on soils. Two lithotypes of calcareous porous rocks were tested. The quasi-steady centrifuge method was used to measure the flux density for different centrifugal driving forces while maintaining essentially constant water content, as required. Any deviations from the direct proportionality of the measured flux and the applied force would indicate a violation of the DB law. Our results show that, for the tested rocks and conditions, no physical phenomena occurred to cause a failure of the DB law.
The water retention function is essential for modeling flow and transport in porous media. Its experimental determination is still challenging because each of the standard methods is limited to partial moisture ranges. The pore-size distribution (PSD) obtained by the mercury intrusion porosimetry (MIP) may be used as a unifying property that spans across the individual ranges of retention properties obtained with standard methods. This study compares the MIP and quasi-steady centrifuge (QSC) methods with standard ones (suction table, evaporation, and dewpoint potentiameter) to determine the retention curves of subsoil clods and calcareous rocks over most of the moisture range. The selected soils, having a relatively rigid structure compared with other soils, are more similar to the rocks even if there is a non-negligible difference in terms of mechanical strength. The QSC, developed for rock samples, was tested for soil to see if the method is also applicable for mechanically less stable media. The porosity characteristics of soil and rock samples showed bi-and trimodal PSDs. The single MIP test allowed describing the mercury retention curve (MRC) for most of the volumetric mercury content range. The MRCs could be used to fill the gaps in the retention curves that occur with the standard retention procedure when switching from one measurement range to the other. The MIP and QSC methods proved to be relatively fast and reliable for measuring a wider range of the retention curve. However, the application of QSC method to soil samples is limited by effects of compaction due to centrifugal force.
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