Some Diesel Exhaust Reactivity Information Derived by Gas Chromatography

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 caused 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 designs, 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. It is questionable if diesel engine hydrocarbons from well-designed engines need be controlled below present levels to reduce smog in metropolitan areas, especially since diesel engines burn less than 10% of the total vehicle fuel used.