Design and Materials for Long-Life Spark Plugs 2006-01-0617
Durability of spark plug electrodes is mainly determined by spark gap widening, caused by electrode wear. The performance of a spark plug strongly depends on the electrode material, the electrode design, and the operating conditions, i.e. temperature, atmosphere, spark energy, and current.
The knowledge about erosion mechanisms of spark plug materials and their dependence on spark plug parameters is of fundamental interest for the development of materials with a high resistance against electrode erosion. Endurance tests were carried out in a compression chamber to study the spark erosion behavior of different electrode materials in the temperature range between 200 and 900°C. The experiments were carried out in pure nitrogen and synthetic dry air. The pressure in the chamber was 7 bar. In pure nitrogen no erosion was observed which suggests that oxidation is the principal mechanism.
The ignitability relies both on the electrode gap and the electrode diameter. Their influence on spark erosion was studied for pure platinum and nickel. Furthermore, the effect of atmospheric pressure and the contribution of different spark discharge phases to the electrode wear were determined. It was found that platinum and nickel show a completely different behavior due to different oxidation mechanisms. This affects both design and material development of new spark plugs.