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Numerical models for a variety of vehicle emission measurement systems have been developed using Mathematica® software. The sampling systems evaluated include the Constant Volume Sampler (CVS) and the Bag Mini-Diluter (BMD). The CVS system was evaluated as the conventional fixed flow rate system and in a number of configurations designed for improved performance. The enhanced CVS system employs flow rate switch between phases and heated dilution air. This system with various other enhancements was also evaluated. The additional enhancements included proportional ambient sampling, dilution air refinement, heating of system including bags, and heated system with dilution air refinement. Lastly, the Bag Mini-Diluter system was evaluated. The purpose of these models is to help determine which system will be the most effective strategy for Ford Motor Company to utilize for SULEV and below emission measurements.

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.

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).

Clean Dry Air and Zero grade air are used for both dilution and analyzer support gas in exhaust gas analysis for emission testing. Variation in the oxygen content can make a significant impact on the accuracy of test results evaluated for Super Ultra Low Emission Vehicle (SULEV) standards. “Air” is often assumed to retain a constant ratio of nitrogen and oxygen - yet typically the oxygen content is not measured on a real time continuous basis. Production, treatment and distribution methods - the compression, purification and pressure management of air, have been shown to be capable of modifying the transient oxygen concentration by more than 10%. The results of the testing performed identify the oxygen variation behavior of several components found in Zero Air systems.

As automakers begin to develop and certify vehicles that meet the California Air Resources Board LEV II and Environmental Protection Agency Tier II Regulations, emissions test cells must be designed and implemented that are capable of accurate low-level measurements. A new test cell has been installed at Ford Motor Company for use in testing vehicles that meet the stringent Partial Zero Emission Vehicle tailpipe requirements (NMOG = 10 mg/mile, NOx = 20 mg/mile). This test cell includes a redesigned Bag Mini-Diluter (BMD), improved analytical benches, an ultrasonic exhaust flow meter with an integrated tailpipe pressure control system, a conventional constant volume sampler (CVS), and a moveable electric dynamometer. The Bag Mini-Diluter will be used as the primary sampling system for the tailpipe measurements. The moveable electric dynamometer enables the test cell to be configured so that the vehicle is moved to the test equipment rather than moving the test equipment to the vehicle.