Intebrake 3-D CFD Transient Simulation Studies for Predicting Flow Performance

This paper presents transient, complex, moving mesh, 3-D CFD analysis of an intebrake lubrication oil circuit for predicting flow performance. Intebrake is a mechanism for improving braking performance during over speeding conditions. The mechanism briefly opens the exhaust valve at the end of a compression stroke with a small valve lift and releases the compressed gases, thereby helping in quick application of the brake. There is no fueling during the process and hence, no combustion induced pressure rise which helps in quick application of the brake. During the intebrake operation, opening of the exhaust valve is achieved by using a complex lube oil circuit inside the exhaust rocker lever. The intebrake lube oil circuit consists of various spring-operated valves with micro-sized clearances, high oil pressure generation up to ~ 250 bar, 3-D movement of the mechanism components, and it is a transient operation. The 3-D movement consists of simultaneous rotational and translational motions with dynamic motions due to net force balance between spring and fluid forces. All these factors make the simulation an absolute need as testing is extremely costly and difficult due to tight space constraints around the mechanism. The 3-D CFD model with automatic intebrake ON and OFF operations makes dynamic mesh motion more complex. In the current work, 3-D CFD simulation approach is developed which can model the intebrake operation by considering dynamic mesh, small clearances, and oil compressibility effects. The predicted intebrake lube system oil pressure is compared with transient, crank angle based test data and the results are found to be in good correlation. This approach has helped in better understanding of the intebrake response to variation of different design parameters and resolving field failures. After a single cylinder intebrake model validation, it has been extended to modeling 6-cylinders and integrated with engine 3-D CFD lube system as well.