Sodium Cooling Efficiency in Hollow Valves for Heavy Duty Engines

As a consequence of the ongoing evolution of engines, where performance is continuously improving and the use of alternative fuels is being adopted by many engine manufacturers, thermal working conditions of the exhaust valves are increasingly critical. In order to better resist the higher temperature levels of the exhaust gases, current development ranges from improvement of the cooling concept for the overall system, new materials for valve set components up to the upgrade of the exhaust manifold material. Change in the design of several valvetrain components due to the increased thermal loads is a logical consequence of this technical evolution process. Hollow exhaust valves filled with Sodium (Na) are a known technology that is widely used in passenger car engines to improve thermal behavior and to avoid the need to change to expensive materials (Ni-base alloys). Nevertheless, shaker-cooling effect of Na for engine speeds below 3.000 [rpm] has been questioned in the past and this technology has not been fully explored in heavy duty (HD) applications [1]. In order to investigate the thermal efficiency or effectiveness and to confirm Na-filled valves as a potential technical solution for thermal issues in HD engines, back-to-back analyses (FEA) and tests (temperature measurements and endurance) were performed, mainly focused on heavy duty spark ignition (SI) engines (gas fueled) and on severe applications of diesel engines.