Abstract
Laboratory gasoline and natural gas reciprocating engine
testing was conducted for spark plugs made with a range of
model, developmental, and commercially available electrode
alloys with and without sparking surface alloy insert pads
(platinum group and novel Cr-based alloys), selected to explore
the effects of a range of electrode alloy thermal, chemical, and
mechanical characteristics on erosion resistance. Extensive
internal oxidation and cracking were observed in both gasoline
and natural gas engine tests, indicative of an inherent degree of
susceptibility of currently used electrode materials when heated
to elevated temperatures, no matter what the ignition
conditions. Highly alloyed heat-resistant alloys with excellent
oxidation resistance in many high-temperature environments
suffered from increased rates of erosion, as the gains in
oxidation resistance were more than offset by hotter running
temperatures resulting from decreased electrode alloy thermal
conductivity. Promising early results were obtained with a
novel Cr-6MgO-0.5Ti-0.3La2O3 insert pad electrode alloy,
investigated as an alternative to Pt or Ir base alloys, which
showed little erosion and good resistance to cracking and
oxidation.
