Evaluation of H ₂ /N ₂ as an Alternative to H ₂ /He for Flame Ionization Detector Mix Fuel 2015-01-2803

The Flame Ionization Detection (FID) is the most sensitive and widely used technology for the measurement of total hydrocarbons (THC). In the automotive emission testing of hydrocarbons, the fuel used for the flame in the FID analyzer is a mixture of hydrogen and helium in the ratio of 40:60. The Environmental Protection Agency (EPA) revised 40CFR part 1065 in April 2014 to include nitrogen as a balance gas alternative to helium for FID fuel mixtures used in the automotive industry. In addition to the balance gas alternative, the FID fuel blend tolerance was decreased from 40±2% to 40±1% (0.39 to 0.41mol/mol) hydrogen to minimize the impact on analyzer response. The feasibility of nitrogen as a FID fuel balance gas was studied and compared with a helium balance gas to understand the relative impact on emission testing. The study evaluated multiple hydrogen concentrations ranging from 38-42% in both balance gases. The FID fuel was also evaluated to determine the impact of hydrocarbon contamination (0-100ppb) on the instrumental response. Hydrocarbon detection was found to be more sensitive to deviations in the fuel composition with nitrogen as a balance gas than with helium. With hydrogen composition at 40±1%, the FID response drifts up to ±6% with nitrogen compared to ±2% with helium as the balance gas. It was observed that the accuracy of the hydrocarbon analysis could be improved further by reducing the blend tolerance of hydrogen with nitrogen as a balance gas relative to helium. Background research on the impact of nitrogen as a balance gas is limited and this evaluation is aimed to study the potential of nitrogen as a replacement to helium in the coming years for FID analyses.