Due to the independent operation between the aftertreatment systems and the engine, the aim of the On Board Diagnostic System (OBD) is to ensure the engine emissions stay within the emissions standards during the whole vehicle useful life. In the case of the heavy duty diesel vehicles that use the Selective Catalytic Reduction System (SCR) or the Exhaust Gas Recirculation System (EGR) as the NOx aftertreatment technologies to meet the stringent emissions levels, the use of sensors in the exhaust pipe is required to control and to monitor the engine emissions.
These are new and great challenges to the national diesel engine developers who are working with these systems to get the homologation certification. Accurate mathematic models within the automotive control strategies are becoming ever more important and are strongly used to monitor the NOx emissions directly (in case of SCR systems using the NOx sensor) or indirectly (in case of EGR systems using the Lambda sensor).
The subject of this paper is to study the operation of the aftertreatment systems, to explore the charactheristics of the NOx and Lambda sensors and to analyse their behaviour in real applications, applying them into the emissions control and monitoring systems to achieve the legal requirements.