Evaluation of On-Board Diagnosis Methods for Three-Way Catalytic Converters

Abstract

On-board diagnosis (OBD) aims at detecting malfunctions of emission-related components of road vehicles. It is required by legislation in United States and the European Union, as it is considered to be beneficial for the reduction of vehicle-related air pollution. On-board diagnosis of the catalytic converter is a challenging task, as it relies on indirect assessments of catalyst activity. Several methods have been proposed for catalyst diagnosis, presenting a varying degree of correlation between the quantities used as OBD indexes and the actual tailpipe emissions. This paper evaluates two methods, with the support of mathematical modeling; in the first one, which is commonly used by vehicle manufacturers, malfunction detection relies on the oxygen storage properties of the catalyst, while in the second, detection relies on the heat released by the chemical reactions in the catalyst. Both are found to be sufficient for the diagnosis of catalytic converters for current legislation requirements. However, the thermal method presents higher sensitivity to low levels of catalyst deactivation and could therefore be more suitable for diagnosis of future, ultra-low-emitting vehicles.

Simulation of a thermoelectric gas sensor that determines hydrocarbon concentrations in exhausts and the light-off temperature of catalyst materials

“…For fast heating up, unburnt exhaust components like hydrocarbons (HCs) and carbon monoxide (CO) are oxidized in the DOC to carbon dioxide (CO 2 ) and water (H 2 O), leading to a faster catalyst light-off (Russell and Epling, 2011). Since the DOC is an emission-relevant device, its correct function has to be monitored to comply with the onboard diagnosis (OBD) regulations (Tsinoglou et al, 2002).…”

“…Alternately, the oxygen content in the exhaust is monitored by lambda probes. Both techniques provide enough accuracy only in a narrow range of DOC operating points (van Nieuwstadt et al, 2005). Furthermore, the functionality of DOCs can be monitored by determining the downstream concentration of exhaust gas components using gas sensors.…”

P5.7 - Simulation of a thermoelectric gas sensor to determine hydrocarbons in exhaust gases and to characterize catalyst materials

“…For example, the diesel oxidation catalyst (DOC) is an important part of such systems due to its passive and active functions for exhaust aftertreatment [2]. Furthermore, the functionality of such components has to be monitored, which is specified in the on-board diagnosis (OBD) regulations [3,4]. In case of the DOC, a hydrocarbon (HC) sensor downstream of the catalyst could determine when the conversion of the converter is sufficient enough.…”