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Understanding Catalyst Overheating Protection (COP) as a Source of Post-TWC Ammonia Emissions from Petrol Vehicle
Technical Paper
2022-01-1032
ISSN: 0148-7191, e-ISSN: 2688-3627
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English
Abstract
TWC exposure to extreme temperature could result in irreversible damage or thermal failure. Thus, a strategy embedded in the engine control unit (ECU) called catalyst overheating protection (COP) will be activated to prevent TWC overheating. When COP is activated, the command air-fuel ratio will be enriched to cool the catalyst monolith down.
Fuel enrichment has been proven a main prerequisite for ammonia formation in hot TWCs as a by-product of NOx reduction. Hence, COP events could theoretically be a source of post-catalyst ammonia from petrol vehicles, but this theory is yet to be confirmed in published literature. This paper validated this hypothesis using a self-programmed chassis-level test. The speed of the test vehicle was set to constant while the TWC temperature was raised stepwise until a COP event was activated. It is observed that at both testing speeds, the ammonia spike identified by a Fourier-transformation infrared analyzer (FTIR) spectrometer accorded well with the COP fuel enrichment command obtained with an OBD scan tool and downstream CO/THC concentrations once the TWC temperature exceeded a certain threshold. This confirms that COP events could result in excessive ammonia emission from petrol vehicles. In addition, a non-negligible impact of the presence of condensed water in the sample line on the quantification of ammonia (particularly on the decay side) was noticed, which could challenge the forthcoming legislation.
Authors
Citation
Wang, X., Li, R., Thomas, D., Wang, C. et al., "Understanding Catalyst Overheating Protection (COP) as a Source of Post-TWC Ammonia Emissions from Petrol Vehicle," SAE Technical Paper 2022-01-1032, 2022, https://doi.org/10.4271/2022-01-1032.Also In
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