In previous work, composite intake valves for use in internal combustion (IC) engines were manufactured by resin transfer molding (RTM) and demonstrated in a fully functional IC engine on a dynamometer. These valves consisted of a high temperature polyimide matrix, LaRC PETI-RFI and PETI-RTM, reinforced with a carbon fiber preform. While this previous work successfully demonstrated the potential for composite intake valves, several issues were noted including limited temperature resistance in the engine combustion chamber. Thermal barrier coatings were considered, but it was hypothesized that co-molded metallic components would both improve the temperature resistance and the durability of the composite valves. In the current work, pre-machined, net-shape metallic caps are added to the composite valve, covering the valve face and seat areas. These caps are placed in the die cavity at the same time as the fiber preform, prior to the transfer of the matrix polymer. In addition to protecting the face of the valve from the temperature of the impinging combustion gases, the continuous metallic cap also provides a heat transfer path to the engine valve seat. Caps of varying geometry were co-molded and studied. The results of this study suggest that a strong fit is generated from the geometry of the cap/composite interface, but that residual stress build-up can be, significant enough to distort the metal cap. Mechanical testing of the valve head stiffness indicates that a measureable improvement may be associated with the metallic cap. Further, fired engine testing confirms the potential of'this modification, suggesting that continuedinvestigation intofiber preform optimization to reduce the effects of residual stress generation at the metal-composite interface could yield a durable lightweight alternative valve.
展开▼
