Effect of MMT® Fuel Additive on Emission System Components: Detailed Parts Analysis from Clear- and MMT®-Fueled Escort Vehicles from the Alliance Study 2005-01-1108

Emission studies and component analyses were carried out on Clear-fueled and MMT^®-fueled 100,000 mile Escort vehicles from the Alliance study [SAE 2002-01-2894]. Previously reported analyses of these vehicles indicated that all differences in emission system performance could be attributed, with a 90% confidence level, to the engine cylinder head, spark plugs, oxygen sensors, and catalysts [SAE 2004-01-1084]. These parts from the Clear and MMT^®-fueled vehicles were further analyzed to determine the root causes of the differences in emission system performance. The intake/exhaust valves, fuel injectors, and EGR valves from the cylinder heads were tested, individually and in groups, for differences in vehicle emission performance. Deposits from the exhaust valves of the MMT^®-fueled vehicle were characterized by X-ray diffraction (XRD) and energy-dispersive X-ray spectrometry (EDX), and shown to resemble Mn₃O₄ with partial substitution of Zn²⁺ for Mn²⁺. Performance tests were run on the spark plugs from the two vehicles. Static and dynamic response characteristics for the oxygen sensors were measured in the laboratory. Sample cores were removed from the catalysts and tested for warmed-up and lightoff performance and oxygen storage capacity. X-Ray fluorescence (XRF) and electron microprobe analyses were also performed on the catalysts to assess the amount and spatial distribution of manganese and other contaminants. Some differences were observed in the spark plugs and HEGO sensors for the two vehicles, but these differences are not believed to have significant impact on vehicle emissions performance. Observed increases in HC and CO emissions for the MMT^®-fueled vehicle are attributable to transient leakage in intake and/or exhaust valves caused by MMT^®-derived deposits on the valves. Higher NO_x emissions observed in the MMT^®-fueled vehicle are caused by reduction in catalyst efficiency due to blockage of some catalyst channels with Mn-containing deposits.