Correlation between Batch (Bag) and Continuous Sampling for N ₂ O Measurement in Diluted Exhaust from Light-Duty Vehicles 2015-01-1993

In the engine and vehicle test procedures described in Parts 1065/1066 of Title 40 of the Code of Federal Regulations (CFR), the United States Environmental Protection Agency (US-EPA) allows for the measurement of N₂O emissions from sample storage bags, from a continuous dilute stream or a raw exhaust stream. Typically, batch (Bag) sampling has better accuracy and repeatability, but continuous sampling is more efficient in terms of test cell running time and provides test-mode emissions with good correlation to bag measurements.

In this study, correlations between bag sampling and continuous dilute exhaust sampling were investigated using a fleet of vehicles with a wide range of N₂O emission levels. Very good correlation between these two sampling methods was observed for the majority of tests conducted. In the best cases, differences in average N₂O concentration levels measured by these two methods were less than +/− 1%. Interferences, analyzer range correlation, accuracy of calibration gas, data sampling speed and other parameters that may influence the difference in N₂O levels measured using the two sampling methods were examined.