In emissions research, hydrocarbon speciation is a powerful tool used to understand the combustion process and to observe the effects of varying gasoline and alternate fuel composition, fuel additives, and emission control hardware. The procedures, which identify and quantify exhaust constituents, can also be used to evaluate evaporative emissions.
Southwest Research Institute (SwRI) performs hydrocarbon speciation of gasoline, reformulated gasoline, and alternative fuel exhaust, identifying approximately 160 individual hydrocarbon components.
Using speciation data, Institute scientists evaluate the relative reactivity of exhaust and evaporative emissions. Different hydrocarbons in urban air form differing levels of ozone (smog) depending on the reactivities of these individual components. To evaluate hydrocarbon impact on ozone formation, complete speciation is required. The procedure also determines the presence and level of toxic emissions from automobiles and other sources.
Using novel sample collection and analysis techniques, SwRI also conducts hydrocarbon speciation for diesel exhaust, which is far more challenging than gasoline exhaust speciation. Diesel exhaust is comprised of hundreds of constituents, far more than are found in gasoline-derived exhaust.
Diesel exhaust consists of heavier hydrocarbons, reflecting the composition of diesel fuel. While gasoline exhaust components typically range from C1 to C12, diesel fuel produces C10 to C22. Because hydrocarbons from C12 to C22 are too heavy to remain in a gaseous state at room temperature, traditional means of capturing exhaust gas samples are inadequate.
To collect samples, SwRI passes diesel exhaust through a cartridge packed with a solid sorbent that efficiently adsorbs hydrocarbons heavier than C10 at moderate temperatures. Samples are subsequently desorbed into an analytical instrument by heating the cartridge while passing helium through it.
Heavy hydrocarbon speciation technology represents an important new development for automotive emissions researchers. The relative reactivity of diesel exhaust emissions can now be compared to those of other fuels. The technology will result in more data related to the effects of diesel fuel reformulation, fuel additives, and exhaust aftertreatment.
Hydrocarbon Speciation Applications
The Institute has conducted partial speciation of automotive exhaust since 1975 and full speciation since 1989. Capabilities now include speciating exhaust from engines and vehicles operating on a variety of fuels, including:
Using data from hydrocarbon speciation, SwRI investigates the effects of fuel properties on automotive exhaust and evaporative emissions to determine relative reactivities and/or toxicities. Hydrocarbon speciation data generated by SwRI helped establish Californias Phase II gasoline requirements and were used in the development of the EPA complex model.
Using speciation data, SwRI researchers have made a number of
nonproprietary observations about the relationships between fuel property modifications
and automotive emissions. While specific fuel reformulations can reduce hydrocarbon
emissions from modern, catalyst-equipped vehicles, they can actually increase emissions
from older vehicles. Some reformulations decrease the total mass of hydrocarbon emissions,
but increase the mass of toxic emissions or increase the overall emission reactivity
(ability to form ozone).
This brochure was published in April 1999. For more information about hydrocarbon speciation, contact Robert Fanick, Phone (210) 522-2653, Fax (210) 522-3950, Engine, Emissions and Vehicle Research Division, Southwest Research Institute, P.O. Drawer 28510, San Antonio, Texas 78228-0510.