Challenges of Measuring Low Levels of CO 2 and NO x on H 2 -ICE

Society is moving towards climate neutrality where hydrogen fuelled combustion engines (H₂ ICE) could be considered a main technology. These engines run on hydrogen (H₂) so carbon-based emission are only present at a very low level from the lube oil. The most important pollutants NO and NO₂ are caused by the exhaust aftertreatment system as well as CO₂ coming from the ambient air.

For standard measurement technologies these low levels of CO₂ are hard to detect due to the high-water content. Normal levels of CO₂ are between 400-500 ppm which is very close or even below the detection limit of commonly used non-dispersive-infrared-detectors (NDIR). As well the high-water content is very challenging for NO_x measuring devices, like chemiluminescence detectors (CLD), where it results in higher noise and therefore a worse detection limit. Even for Fourier-transformed-infrared-spectroscopy-analysers (FT-IR) it is challenging to deal with water content over 15% without increased noise.

The goal of this study was to show that measuring low levels of CO₂ and NO_x can be performed by FT-IR. Therefore, new calibrations are created for NO, NO₂ and CO₂. These were first tested by calibration gases in wet and dry conditions. Afterwards a 2l four-cylinder passenger car engine that is run on hydrogen was used to generate real engine data. The engine is equipped with a state-of-the-art SCR catalyst system. The FT-IR analyser was compared to theoretical data as well as to a standard CLD and NDIR. Several steady-state points were performed as well as a driving cycle.

The results show a large improvement in reducing the noise caused by high water and therefore a more accurate measurement at low concentrations. Measured concentrations as well as masses show a good alignment with expected values.