1990-02-01

Ceramic Piston-Cup: Design and Testing 900402

In this work, the design and testing of a silicon-nitride (Si3N4) piston-cup for a Petter AV1 laboratory diesel engine is presented.
A preliminary design was first prepared and tested for thermal shock. The tests showed that non uniform displacements occurred between the ceramic plate and the piston. An improved design was then prepared, which allowed control of the characteristics of the gasket mounted between the ceramic plate and the piston. This second design was evaluated by thermal shock and exposure to cyclic pressure variation, followed by engine tests.
A short description is given of the experimental set-up used for investigating the ceramic materials which are candidates for the moving parts exposed to thermal and dynamic shock in internal combustion engines. Finally two pistons with ceramic top plates were introduced in the engine with thermocouples mounted at different points of the liner and exhaust valve.
It was concluded that while the ceramic has superior characteristics, mounting of the ceramic plate on the piston was not satisfactory and must be modified.
During the last few years great progress has been reported in material processing, high temperature properties and design methodology for I.C. engine ceramic components. [1, 2, 3 and 4]*. The understanding and the improvement of the mechanical reliability increased the commercialization and the successful use of ceramic components in the automobile engine [5]. However the mass-production cost of high performance components is certainly the most important limitation for wider appllication of these materials in heat-engines. Therefore further studies and development covering all aspects of this technology should be carried out for successful application.
This work covers the design and testing of a silicon-nitride piston-cup including computer aided design, materials selection, prototype manufacturing.
assembly and joining, proof and bench testing. The integral casting has been used to mount the ceramic piston-cup in an aluminium adaptor, connected to the aluminium piston, and supported by a specially fitted gasket.
Designing components to operate in compression stress has been found to be a valid strategy for avoiding tensile stress failure in engine components. The use of casting technology for metal-ceramic joining to establish these beneficial assembly stresses is doubly attractive, since this way it eliminates the need for close tolerances in the metal component and reduces the tolerances required of the ceramic part.
In this paper the improvements of the preliminary design after the test results are discussed.

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