Contact systems for use in sulfur containing, reformulated gasolines

As part of the overall effort to reduce pollution effects associated with automotive emissions, government mandates have required a reduction in the sulfur level of gasoline. This has required changes in the refining process. Along with a reduction in overall sulfur levels, the new process also produces an apparent change in the chemistry of the residual sulfur species. Although not yet fully characterized, initial data suggests that this newer species is chemically more reactive than the older form. With sensors using conventional Ag and Pd-Ag contact materials, signal noise is much higher in the newer gasolines even with the reduced ppm sulfur levels. Similar results were also found with higher ppm sulfur fuels from countries, such as Australia, South Africa, and Malaysia, where the gasoline formulations or distribution/refining conditions may not tightly as tightly controlled. SEM data indicates the noise is associated with the formation of sulfide surface films. In order to provide long term, noise free signals in these newer fuels, a new family of Au based contact materials and a complimentary thick film ink has been developed to overcome these issues. Test data is provided to show the improved performance of these new materials in an accelerated test using a fuel doped with 20 ppm elemental sulfur.