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The use of Selective Catalytic Reduction (SCR) for NOx emissions control has resulted in a new challenge for the emissions measurement community. Most SCR systems require injection of urea or ammonia into the exhaust stream. Residual ammonia present in vehicle exhaust can have deleterious effects on NOx analyzers using chemiluminescent detectors (CLD). Ammonia can poison converter catalysts in CLD NOx analyzers and may react with NO2 across the converter. Both of these issues lead to erroneous NOx measurements, as well as increased maintenance costs and downtime. This paper will describe the development and use of a low-cost, simple ammonia scrubber that can easily be integrated into sampling systems and requires little change in test cell maintenance procedures. Validation results show the scrubber to have capacity sufficient to last for a full day of testing of typical vehicles.

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.