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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 treatments to produce bags that reduce contamination. Based on the average emission rates, baked Tedlar®, Capran® treated with alumina deposition, supercritical CO2 extracted Kynar® and supercritical CO2 extracted Teflon NXT are capable of achieving the target hydrocarbon emission rate of less than 15 ppbC per 30 minutes. CO2 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 CO2 concentration, ease of sealing, and ease of surface treatment, none of the four materials could be distinguished from one another.

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.

This paper presents a technique for examining “Goodness of Fit” of polynomial least square curves using “errorless” data. (The errors in “real world” data tend to mask a polynomial curve's lack of fit). A method of assessing the “quality” of real data before attempting to fit a curve to the data is also presented. If data “quality” proves satisfactory, a cubic spline curve can be generated which provides a much better fit to the data than can ever be attained using polynomial curves.

The Automotive Industry/Government Emissions Research CRADA (AIGER) has been working to develop a new methodology for the direct determination of nonmethane hydrocarbons (DNMHC) in vehicle testing. This new measurement technique avoids the need for subtraction of a separately determined methane value from the total hydrocarbon measurement as is presently required by the Code of Federal Regulations. This paper will cover the historical aspects of the development program, which was initiated in 1993 and concluded in 2002. A fast, gas chromatographic (GC) column technology was selected and developed for the measurement of the nonmethane hydrocarbons directly, without any interference or correction being caused by the co-presence of sample methane. This new methodology chromatographically separates the methane from the nonmethane hydrocarbons, and then measures both the methane and the backflushed, total nonmethane hydrocarbons using standard flame ionization detection (FID).

Recent papers have investigated the influence of sample composition on Flame Ionization Detector (FID) instrumentation used to measure total hydrocarbon content in exhaust emission samples. In this paper we describe experiments and results that further define these effects. Specially blended propane in air cylinders were crafted to provide a nominal 3 ppmC propane concentration with an oxygen content ranging from 17.5 vol % to 21 vol%. These cylinders were evaluated on multiple FID designs and then used to evaluate a strategy to correct the effects of the interaction. The study shows that, in general, most FID's behave similarly in response to changing oxygen content in the presence of hydrocarbon. Anomalies are discussed. The cylinders are then used to demonstrate that a proposed method for correcting the oxygen and hydrocarbon interaction is successful in reducing the effects.