The Impact of Ash Forming Lubricant Additives on NOx Sensor Performance

摘要

Ash forming compounds derived from the combustion of fuel and. from engine lubricants have the potential to foul NO_x sensors. A study was conducted with diesel truck engines to evaluate the impact of these ash forming compounds on NO_x sensor fouling. Engines were operated with diesel fuels and lubricant oils composed of different chemical compositions. Sensors were installed in the exhaust systems of laboratory diesel engines during dynamometer tests. During operation of the laboratory engines, the NO_x sensor output signals were monitored. The accuracy and response rates of sensors were measured prior to the tests and upon the completion of the tests, showing no deteriorating trends. After a substantial amount of engine running hours, NO_x sensors were removed from the exhaust system for further inspection. Certain sensors were cut open and analyzed for deposits in active NO_x sensor surfaces. Analysis showed elevated concentrations of Calcium, Phosphorous, Iron and Magnesium at the outer surface of the measuring element. At the inside surface, however, no elevated concentrations of ash forming elements were detected causing no impact on overall NO_x sensor performance.