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Natural Gas Vehicles: Impact of Fuel Composition on Vehicle Performance and Emissions
Published June 01, 1997 by ISATA - Dusseldorf Trade Fair in United Kingdom
Event: ISATA 1997
To promote successful commercialization of natural gas vehicles (NGVs), several utilities, automakers, and regulatory agencies joined forces in 1995-96 to determine how NGV emissions and performance are affected by variations in motor-fuel grade natural gas composition.
In rigorous tests at the Clean Air Vehicle Technology Center (CAVTC) in Hayward, California, nine light- and medium-duty NGVs were each run through FTP and US06 test cycles on five different blends of natural gas, including the California certification fuel. Vehicles were selected to establish a representative sampling of dedicated~designed, engineered, and optimized by the original equipment manufacturer (OEM) to run only on natural gas~and bi-fuel models equipped to operate on either natural gas or gasoline. Fuel blends included the California Air Resources Board (CARB) certification gas, common commercial blends, and other representing "fringe" compositions with relatively high concentrations of ethane and heavier hydrocarbons (i.e., C2+) and inerts (i.e., 6-11% N2 and CO2). The "fringe" compositions are unlikely to be encountered by consumers, and were included as boundary conditions.
Results showed only minor impacts of fuel variability, insignificant in vehicles with sophisticated systems integration. The dedicated NGVs performed well on all fuels. The differences among fuels caused only slight variations in emissions and virtually no change in performance. The bi-fuel vehicles~which have higher emissions and lower performance than dedicated NGVs~also exhibited little change in emission or performance as a function of fuel variability. With all the fuels tested, all vehicles produced emissions well below the stringent CARB limits.
Overall, this research suggests that existing natural gas motor-grade fuel specifications may be unnecessarily restrictive. Standard products of natural gas utilities may be suitable for vehicular use. If this finding is verified by CARB, the current specifications for natural gas vehicular fuel should be reexamined.