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The effects of API SE engine oils on the activity of a 1975 prototype monolithic, noble metal oxidation catalyst have been studied in long-term multicylinder laboratory engine tests. Results of this work showed that oil consumption rates, up to 1 qt/100 miles, and lube ash up to 1.6%, do not significantly affect catalyst activity in 500 hour tests, equivalent to 20,000 miles (32,180 km). A higher-than-normal phosphorus-containing oil (0.32% P) caused significant loss in catalyst activity after testing for 30,000 miles (48,270 km). This suggests that any need for increased phosphorus-containing additives in future oils could cause catalyst poisoning before 50,000 miles.

Chromatographic analysis of diesel exhaust indicates a number of low molecular weight hydrocarbons, below C6. Using reactivity index as a criterion, much of the diesel exhaust reactivity can be attributed to ethylene and propylene lausnd by the thermal decomposition of the fuel. Hydrocarbons in the C4-C7 range, including high relative reactivity olefins, are generally low in volume concentration and therefore contribute little to the overall exhaust reactivity. Hydrocarbons, in terms of parts per million carbon above C7, are low in present diesel engine design, so individual volume concentrations are generally fractional parts per million. Reactivity per horsepower hour from diesel engine exhaust is less than that from the one small industrial gasoline engine tested by the heavy-duty truck diesel engine cycle. /GMRL/