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The Flame Ionization Detector (FID) used to measure hydrocarbon content in emission samples uses a hydrogen flame that produces little ionization. Hydrocarbons introduced into this flame produce large numbers of ions with ionization proportional to the number of carbon atoms present. This proportionality can be skewed by variations in oxygen content. Oxygen variation in emission samples, cylinders of air or span/calibration gas, and zero air systems are investigated and their effects on emission results are discussed. The oxygen content of the gas under analysis will affect the hydrocarbon concentration reported by the FID. In the example examined in this paper, the oxygen effect was shown to decrease the FTP (Federal Test Procedure) weighted NMHC (Non-Methane Hydrocarbon) results by as much as 7 % for a BMD (Bag Mini-Diluter) sample and 13% for a CVS (Constant Volume Sampling) sample.

For the past several years, manufacturers have been developing emission measurement systems for Super Ultra Low Emission (SULEV) measurements. The Bag Mini-Diluter (BMD) with an advanced exhaust flow measurement device is designed as an alternative to the traditional method for sampling vehicle exhaust, the constant volume sampler (CVS). Exhaust sampling instruments require system verification tests. The system verification test described and mandated for the CVS in the Code of Federal Regulations (CFR) §86.119-90(c) is a simulated test with propane. The very low concentration measurements required for SULEV regulations demand a more enhanced and accurate verification technique and procedure than the method described in the CFR. This investigation focuses on the technique and necessary equipment for verifying system integrity of the entire emission sampling system, including the Bag Mini-Diluter and the exhaust flow measurement device in the test cell.