A Study on the Flow Resistance of Fluids Flowing in the Engine Oil-Cooler Chosen

Oil-coolers are necessary components in high performance diesel engines. The heat removed by the cooler is a component in the total heat rejection via the engine coolant. Oil-cooler absorbs the heat rejected during the piston cooling and engine rubbing friction power loss. During flows of both coolant and engine oil via the oil-cooler, some flow resistances occur. The aim of the study is to determine values of the flow resistance coefficient for oil going through the cooler at various temperatures. The test stand was developed to determine time needed to empty tanks from liquids flowing through oil-cooler. The flow model was elaborated to study the mentioned flow resistance coefficient with respect to changing liquid temperature. The 20 °C increase in liquid temperature resulted in a flow resistance coefficient decrease of 30% for coolant and of the much more for engine oil. It was found that better results would be achieved with flows forced by means of pumps instead of using gravitational forces on the test stand.

Simulation of the oil supply through the connecting rod to the piston cooling channels in medium speed engines

The importance of the oil flow simulation in connecting rod oil channels during the engine development process is recently increasing. This can be observed either in medium speed engines, where, as one of the traditional solutions, the oil for piston cooling is supplied through the connecting rod, or in automotive engine VCR (variable compression ratio) connecting rods, where engine oil is used to change the compression ratio of the engine. In both cases, precise numerical results are necessary to shorten the prototyping period and to reduce the overall development cost. The multi-physics character of the simulation problem basically consists of the interaction between the dynamics of the crank train components and the oil flow. For the oil supply to the piston cooling channels through the connecting rod in medium speed engines, being the objective of this paper, a major influencing factor is the oil pressure behavior in the piston cooling gallery providing periodical interaction with its supply. At the same time, the connecting rod elastic deformation during engine operation can be regarded as negligible and the planar motion of the connecting rod can be reproduced by combination of translational and rotational acceleration fields in the CFD solver. The paper includes the description of the applied simulation approach, the results and a comparison with the state-of-the art calculation without consideration of the above-mentioned influencing factors.

Numerical and experimental investigation on the effect of the two-phase flow pattern on heat transfer of piston cooling gallery

To study factors affecting the formation and conversion of two-phase flow pattern as well as the heat transfer of piston cooling gallery, a transient visual target test bench was set up to research the oscillatory flow characteristics in the cooling gallery under idle condition of the engine. The computational fluid dynamics (CFD) was employed while dynamic mesh technology, SST k–ω turbulence model and volume of fluid (VOF) two-phase flow model were applied to simulate the flow process of piston cooling gallery so as to predict the distribution pattern of two-phase flow. Simulation results were in good agreement with that experimentally obtained. It was observed that in the reciprocating movement of the piston, the action of two-phase flow oscillation was severe, forming some unstable wave flows and slug flows. Results show that under the same pipe diameter, the increase of fluid viscosity results in the decrease of amplitude and the increase of the liquid slugs number as well as the enhancement on heat transfer effect. In addition, it was revealed that injection pressure has little effect on the two-phase flow pattern. However, when the pressure is reduced, the change of the liquid phase is weakened and the locations of flow pattern transition move towards to the behind, thus the impact on the heat transfer is also faint.

Heavy Duty Engine Piston Cooling Gallery Oil Filling Ratio Measurement and Comparison of Results With Simulation

Pistons for heavy duty diesel applications endure high thermal loads and therefore result in reduced durability. Pistons for such heavy duty applications are generally designed with an internal oil gallery — called the piston cooling gallery (PCG) — where the intent is to reduce the piston crown temperatures through forced convection cooling and thereby ensure the durability of the piston. One of the key factors influencing the efficiency of such a heat-transfer process is the volume fraction of oil inside the piston cooling gallery — defined as the filling ratio (FR) — during engine operation. As a part of this study, a motoring engine measurement system was developed to measure the piston filling ratio of an inline-6 production heavy duty engine. In this system, multiple high precision pressure sensors were applied to the piston cooling gallery and a linkage was designed and fabricated to transfer the piston cooling gallery oil pressure signal out of the motoring engine. This pressure information was then correlated with the oil filling ratio through a series of calibration runs with known oil quantity in the piston cooling gallery. This proposed method can be used to measure the piston cooling gallery oil filling ratio for heavy duty engine pistons. A preliminary transient Computational Fluid Dynamics (CFD) analysis was performed to identify the filling ratio and transient pressures at the corresponding transducer locations in the piston cooling gallery for one of the motoring test operating speeds (1200 RPM). A mesh dependency study was performed for the CFD analysis and the results were compared against those from the motoring test.