HIGH-RESOLUTION GAS-CHROMATOGRAPHIC DETERMINATION OF THE ATMOSPHERIC REACTIVITY OF ENGINE-OUT HYDROCARBON EMISSIONS FROM A SPARK-IGNITED ENGINE

The reactivities of engine out exhaust hydrocarbon (HC) emissions in p hotochemical smog formation have been determined for three fuels (isoo ctane, an aromatic blend, and a gasoline) in a single-cylinder, spark- ignited engine. High resolution capillary GC was used to determine the mole fractions of the exhaust hydrocarbon species. Temperature progra mmed chromatography on a single capillary column was sufficient to sep arate the major exhaust species. A library of approximately 160 hydroc arbon species was used to identify typically 90-95 % of the HC species present. GC-MS was used selectively to verify peak assignments.The ef fect of engine operating parameters (fuel-to-air ratio, spark timing, and speed) on reactivity was examined. Engine operating parameters aff ect both total emissions [g/mile] and the specific atmospheric reactiv ity [g ozone/g HC emissions] of these emissions. Changing the operatin g parameters to control total emissions may not be as effective as exp ected in controlling the total reactivity [g ozone/mile] of the emissi ons because the specific reactivity can also change simultaneously. Ef fects of changes in operating parameters differ significantly as the t ype of fuel is varied. The ability to measure exhaust hydrocarbon spec ies emissions accurately and quickly will increase in importance as re activity-based emissions standards come into widespread use.