Challenges of measuring low levels of CO2 and NOx on H2-ICE 2024-01-2998

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 NOx 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 NOx 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. Therefore ammonia (NH3) and nitrous dioxide (N2O) where measured as well. 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 different driving cycles. 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. Ongoing tests are performed to see if the calibrations can be further approved.