Low-temperature NOx reduction by H2 in diesel engine exhaust
2022-01-0652
03/29/2022
- Content
- For NOx removal from diesel exhaust, selective catalytic reduction (SCR) and lean NOx traps are established technologies. However, these procedures lack efficiency below 200°C, which is of importance for city driving and cold start phases. Thus, the present paper deals with the development of a novel low-temperature deNOx strategy implying the catalytic NOx reduction by hydrogen. For the investigations, the best available H2-deNOx catalyst, originally engineered for lean H2 combustion engines, was employed. This Pt-based catalyst reached peak NOx conversion of 95% in synthetic diesel exhaust with N2 selectivities up to 80 %. Additionally, factors inhibiting H2-deNOx, such as high CO/HC contents, were identified and eliminated by applying an efficient diesel oxidation catalyst upstream of the H2-deNOx stage. Transient runs on a diesel engine test bench with a full size H2-deNOx catalyst using WLTP, CADC UC and TfL UIP driving cycles revealed NOx conversions of up to 90 % at temperatures as low as 80 °C. However, outside the low-temperature region, deNOx dropped significantly evidencing the need for an additional tailpipe-end SCR system. Moreover, slight N2O formation was observed in the engine tests making further catalyst development necessary, since N2O is considered a critical component due to its global warming potential. Additionally, hydrogen demand for H2-deNOx in diesel passenger cars was determined and a novel on-board production strategy based on DEF/AdBlue electrolysis developed. Subsequent simulations demonstrate small form factors (≤ 525 cm³) and rather low energy consumption of the H2 supply unit, e.g. 0.25 kWh for the TfL driving cycle.
- Citation
- Esser, E., Kureti, S., Heckemüller, L., Todt, A. et al., "Low-temperature NOx reduction by H2 in diesel engine exhaust," SAE Technical Paper 2022-01-0652, 2022, .