Browse Publications Technical Papers 2019-01-0076
2019-01-15

Effects of Isotopic Calibration Gases on IR Quantification Analyzer Techniques to Measure CO and CO2 in Engine Emissions Testing 2019-01-0076

Authors: Anuj Kumar1, Bertold Arlitt2, and Tracey Jacksier1 1Air Liquide, Delaware Research & Technology Center, 200 GBC Drive, Newark, DE 19702 2AVL Emission Test Systems GmbH, Max-Roth-Str. 1, D - 76571 Gaggenau, Germany Infrared spectroscopic methods are the most common methods in the automotive industry to measure carbon monoxide (CO) and carbon dioxide (CO2) gases. Both gases, which are emitted from the combustion of fuels, are required to be determined accurately in order to follow strict environmental regulations. Appropriate analytical techniques and accurate calibration gas mixtures are therefore critical for successful measurement. Regulatory documents such as the EPA's Code of Federal Regulations 40 (CFR 40) part 1065.250, UN ECE-R83, and (EU) 2017/1151 recommend a nondispersive infrared (NDIR) analyzer to measure CO and CO2 concentrations in raw or diluted exhaust samples. Over the last decade, Fourier Transform Infrared (FTIR) spectrometry has also been validated and recommended in engine exhaust certification testing as well as engine and vehicle development activities. Thus far, there has been a limited focus on the effect of isotopic CO or CO2 calibration gas mixtures in engine emissions testing. In the present work, up to 4% deviation in analytical results were observed relative to the natural composition (1.10% 13CO) when 13C in CO/N2 gas mixture varied between 0.05 to 3.92% using an IR analyzer. Additionally, analytical deviation was more pronounced (4-14%) relative to the natural composition when 13C in the CO2/N2 varied in the range of 0.02 to 8.04%. Even though calibration gases are prepared accurately for molecular concentrations, non-natural carbon isotopic concentrations may pose significant errors in the measurements. The variation in the isotopic ratio of C12/C13 in natural CO2 sources is in the range of ± 2‰ however, artificial sources of CO or CO2 can potentially have much larger variance. It is, therefore, essential to have a natural ratio of carbon isotope calibration gas mixtures for accurate emission measurements.

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