Characterization of erosion and failure processes of spark plugs after field service in natural gas engines

Microstructural and optical spectroscopic analyses were carried out on as-received and used spark plugs after field service in natural gas (NG) reciprocating engines. The objective of this work was to examine the corrosion and erosion mechanisms of natural gas engine spark plug as well as identify the primary life limiting processes during field operation. The optical emission spectroscopic analysis showed a strong Ca signal in the exposed spark plugs and scanning electron microscopy showed substantial formation of Ca-enriched glassy oxide phase(s) on the electrode surfaces. In addition, intergranular cracking was observed in the subsurface region of both iridium (Ir) and platinum-tungsten (Pt-W) alloy electrode insert tips. The coalescence and subsequent growth of these cracks would accelerate the wear of the electrodes and shorten the lifetime of the spark plugs. Also, extensive internal oxidation and subsequent crack generation occurred along the interface between Ni-base alloy electrode and Pt-W alloy tip insert during field service, which would result in substantial degradation in the ignitability and performance of the electrodes, and thus spark plug failure.