The US Environmental Protection Agency (EPA) currently regulates NOx measurement using Chemiluminescent Detectors (CLDs), Non-dispersive Ultraviolet (NDUV) analyzers, and Zirconia Oxide (ZrO2) analyzers, as outlined in the 40 CFR Part 1065 (Subparts 207, 272, and 274). These methods function well in both direct and dilute sampling systems. However, a key challenge associated with these techniques is the indirect measurement of NO2. Common practice is to use dual-CLDs; one CLD dedicated to measure the NO and another CLD coupled with a catalytic converter to convert all NO2 to NO and then measure the total NOx. It often involves mathematically subtracting NO from total NOx, which can be susceptible to errors due to time delays in the measurement of NO and NOx can lead to inaccurate NO2 calculations. The converters can degrade over time, further impacting accuracy.
In this study an alternative procedure for NOx measurement utilizing an advance Infra-red Laser Absorption Modulation (IRLAM) technology was proposed. This approach offers several advantages over conventional methods such as directly measures both NO and NO2 concentrations, eliminating the need for the use of an NOx converter and mathematical subtraction. Total NOx is simply calculated by summing the directly measured NO and NO2 values, streamlining the process and avoiding potential time alignment and calculation errors.
The primary objective of this study is to compare the advance IRLAM technology with conventional CLD by collecting a statistically significant set of certification-quality nitrogen oxides (NOx) emissions data in compliance with the requirements of 40 CFR 1065.12(d) and (e) from heavy-duty engines (HDE) and light-duty vehicles (LDV) for the current model year through 2032 during certification testing. In all cases, care was taken to select datasets that accurately reflect the precision of the measurement procedure. For paired datasets, all measurements were performed using the same engine, measurement instruments, and test cycle to ensure consistency.
The results demonstrate no statistically significant difference between the measurements obtained from the two devices, 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.
In summary, the IRLAM technology offers significant advantages for the automotive industry regarding NOx measurement. These advantages lead to improved data quality and potentially lower costs. Unlike chemiluminescent detectors, IRLAM eliminates the need for NOx converters, a source of error due to conversion efficiency and required periodic checks (40 CFR 1065). IRLAM represents a next-generation wet measurement technology that eliminates "quench errors" entirely, ensuring reliable data. IRLAM technology boasts exceptionally low interference levels, well below any potential quench values, further enhancing data integrity.