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The Automotive Industry/Government Emissions Research CRADA (AIGER) has been working to develop a new methodology for the direct determination of nonmethane hydrocarbons (DNMHC) in vehicle testing. This new measurement technique avoids the need for subtraction of a separately determined methane value from the total hydrocarbon measurement as is presently required by the Code of Federal Regulations. This paper will cover the historical aspects of the development program, which was initiated in 1993 and concluded in 2002. A fast, gas chromatographic (GC) column technology was selected and developed for the measurement of the nonmethane hydrocarbons directly, without any interference or correction being caused by the co-presence of sample methane. This new methodology chromatographically separates the methane from the nonmethane hydrocarbons, and then measures both the methane and the backflushed, total nonmethane hydrocarbons using standard flame ionization detection (FID).

Bench reactor experiments were carried out to investigate the effects of operating temperature, precious metal loading, space velocity, and air-fuel (A/F) ratio on the performance of palladium (Pd) catalysts under simulated natural gas vehicle (NGV) exhaust conditions. The performance of these catalysts under simulated gasoline vehicle (GV) conditions was also investigated. In the case of simulated NGV exhaust, where methane was used as the prototypical hydrocarbon (HC) species, peak three-way conversion was obtained under richer conditions than required with simulated GV exhaust (propane and propene HC species). Moreover, the hydrocarbon efficiency of the catalyst under simulated NGV exhaust conditions was more sensitive to both A/F ratio and perturbations in A/F ratio than the HC efficiency under GV exhaust conditions.