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Individual hydrocarbon conversion efficiencies of engine-out emissions have been measured for four different catalyst formulations (Pd-only, trimetallic, Pd/Rh, and Pt/Rh) during stoichiometric and rich operation. The measurements were carried out as a function of fuel-air equivalence ratio (Φ) using a dynamometer-controlled 1993 Ford V8 engine and capillary gas chromatography. HC conversion efficiency was examined in terms of mass conversion efficiency and also using three new definitions of catalyst conversion efficiency. The efficiencies across the four catalysts show similar trends with Φ for almost all HC species. The catalyst efficiencies for alkanes, alkenes, and aromatic species decrease as Φ increases above stoichiometric: alkane efficiencies decrease faster than alkenes which in turn decrease faster than aromatics. All efficiencies fall to zero near Φ = 1.08 except those of MTBE and acetylene, which remain near 100%.

The Texas Project was a multi-year study of aftermarket conversions of a variety of light-duty vehicles to CNG or LPG. One aspect of this project was to examine the factors that influence the economics of fleet conversions to these alternative fuels. The present analysis did not include longer-term effects (such as possible increases in exhaust system life or increases in tire wear). Additionally, assumptions were required to estimate the costs of repairs to the alternative fuel system and engine. Other factors considered include conversion cost, fuel prices, annual alternative fuel tax (as applied for the state of Texas), annual miles accumulated, and the percent miles traveled while using the alternative fuel for dual fuel conversions.

On occasions automotive fuels have been contaminated by adventitious admixtures of silicon (Si)-containing compounds which have deleterious effects on automotive catalysts and oxygen sensors. The deactivation of monolithic automotive catalysts by fuel-derived silicon is due to deposition of crystalline silica (∝-SiO2) on the catalyst surface which causes mass transfer limitations and may ultimately result in plugging of the monolith. Stoichiometric conversions efficiency of three-way catalysts (TWCs) from various low-mileage vehicles were significantly deteriorated; e.g., from typical three-way efficiencies of −95% conversion to <50% conversion at 550°C after only 1500 mi of vehicle use. Laboratory aging of a TWC exposed to combustion products of isooctane fuel containing 20 ppm Si resulted in a continual decline in three-way conversions to <40% after 15,000 simulated miles.