Michael T. Sherman

Flame ionization detector oxygen quench effects on hydrocarbon emission results

The Flame lonization 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. The effects of oxygen content from zero gas, span gas and calibration gas are much smaller than the effect from a bag sample. The oxygen content effect is greater than the hydrocarbon concentration effect in the concentration region where SULEV (Super Ultra Low Emission Vehicle) exhaust samples are measured.

An Investigation of Sample Bag Hydrocarbon Emissions and Carbon Dioxide Permeation Properties

The equipment for collecting dilute exhaust samples involves the use of bag materials (i.e., Tedlar®) that emit hydrocarbons that contaminate samples. This study identifies a list of materials and tre tments to produce bags that reduce contamination. Based on the average emission rates, baked Tedlar®, Capran® treated with alumina deposition, supercritical CO 2 extracted Kynar® and supercritical CO 2 extracted Teflon NXT are capable of achieving the target hydrocarbon emission rate of less than 15 ppbC per 30 minutes. CO 2 permeation tests were also performed. Tedlar, Capran, Kynar and Teflon NXT showed comparable average permeation rates. Based on the criteria of HC emission performance, changes in measured CO 2 concentration, ease of sealing, and ease of surface treatment, none of the four materials could be distinguished from one another. Additional information from further testing would need to be added to the results of this study in order to choose a single optimum sample bag material for vehicle emission testing.