Alternative to Hydrogen/Helium as Flame Ionization Detector Fuel 2013-01-1045

Flame ionization detector (FID) analyzers used in emission testing to measure total hydrocarbon emissions have been operating for the last forty years on a fuel mixture of 40% H₂ and 60% helium. These mixtures were selected based on research studies reported in the literature indicating that this particular mixed fuel combination gave the best sensitivity and relative response of the different hydrocarbons present in vehicle exhaust with respect to propane, the calibration gas.

During the past few years, it was announced that there is a worldwide shortage of helium which triggered the automotive industry to look for alternatives for helium to be used in FID fuels. Helium which is produced as a byproduct from natural gas fields is non-renewable, expensive, and extremely rare on the earth. Current supply cannot keep up with demand. There are only few natural gas fields producing helium and unless new natural gas fields are found, current helium amounts will continue to dwindle. Estimates indicate that the private reserves may run out within the next ten years or so. Meetings with gas suppliers over the past few years led to the conclusion that a suitable alternative to helium for FID Fuel must be investigated.

In this study, several alternative candidates to H₂/He were considered: Hydrogen/Nitrogen, Hydrogen/Argon and 100% Hydrogen. This paper discusses these different options and describes the testing performed to evaluate these different candidates to determine the best performing alternative fuel. Linearity, relative response with respect to propane and 10 to 90% response time were used to evaluate the different candidate alternative fuels. The evaluation was performed on bag, modal and heated Emerson/Rosemount Flame Ionization Detector (FID) analyzers. Bag dilute and modal vehicle hydrocarbon emission data with different fuels were collected simultaneously on modified FID analyzers operating on H₂/N₂ and a conventional H₂/He FID analyzers for direct comparison. A heated Rosemount hot FID was also converted to operate on H₂/N₂ and evaluated with continuous dilute HC measurement on a dilution tunnel with a diesel correlation vehicle. The impact on mass emissions at the standards were evaluated and discussed.