The contribution of ceramography to the development of ceramic spark plug electrode materials for large gas engines

Large gas engines play a key role in energy supply and transport. Due to emission regulations and high fuel prices, engines achieving both high efficiency and low emissions are required. Development efforts to that effect have resulted in combustion methods relying on lean air-fuel mixtures as well as high ignition pressures. The conditions in the combustion chamber cause high wear on the spark plug electrodes. Conventional electrodes have a limited lifetime and they are expensive due to the use of precious metal alloys. Compared with conventional materials, alternative ceramic electrode materials offer advantages in terms of high thermal stability, high oxidation and corrosion resistance, as well as lower material prices. Disadvantages include insufficient electrical conductivity, brittleness and the difficulty of joining them with metallic materials. In this paper wear and oxidation behavior of selected materials are evaluated, using ceramographic methods. Microsections of the joining zone are used to analyse the change in the microstructure resulting from the bonding process. The results show the strengths, weaknesses and limitations of the selected ceramics as electrode materials, based on ceramographic methods, which helped essentially to understand the oxidation behavior, the bonding process and wear.