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.