IRLAM-An Advanced Technology for NO x Measurement from Diluted Exhaust of a Light Duty Vehicle (LDV)

The United States Environmental Protection Agency (US-EPA) requires nitrogen oxides (NOx) measurement using Chemiluminescent Detectors (CLDs), Non-dispersive Ultraviolet (NDUV), and Zirconia Oxide (ZrO₂) analyzers, as outlined in the 40 CFR Part 1065. Quantification of NO₂ by CLD requires dual-CLDs; one dedicated to measuring the NO and another coupled with a NO₂-to-NO converter to measure the total NOx. Measurement by using dual-CLDs involves mathematically subtracting NO from total NOx to get NO₂ information. This requires perfect time alignments of both CLDs assigned for measuring NO and NOx to maintain accurate NO₂ calculations. The NO₂-to-NO converters can degrade over time and need to be replaced to get accurate total NOx measurement. In this study, Infra-red Laser Absorption Modulation (IRLAMTM) technology, which is an advanced QCL-IR spectroscopy proposed in the previous study [1], is used to measure NO and NO₂ simultaneously in the exhaust gas of light-duty vehicles. This approach offers several advantages such as direct measurement of both NO and NO₂ without a NO₂-to-NO converter. The primary objective of this study is to compare IRLAM technology with conventional CLD by collecting a statistically significant set of certification-quality NOx emissions data in compliance with the requirements of 40 CFR 1065 from diluted exhaust of a MY2024 SULEV light-duty vehicles during certification testing. The results demonstrate no statistically significant difference between the measurements obtained from the two methodologies, establishing IRLAM as a suitable candidate for an alternate procedure for NOx measurement during certification testing. The t-values for all duty cycle populations were consistently below the critical t-values at both 90% and 95% confidence intervals. The f-test values for all duty cycle populations were consistently lower than the critical f-values at both 90% and 95% confidence intervals.