Model Based Assessment of Real-Driving Emissions: A Variation Study on Design and Operation Parameter 2019-26-0241
In 2017 the European authorities put into effect the first part of a new certification test procedure for Real Driving Emissions (RDE). Similar tests are planned in other regions of the world, such as the upcoming China 6a/6b standards, further tightening emission limits, and also the introduction of RDE tests. Both restrictions pose challenging engineering tasks for upcoming vehicles. RDE certification tests feature significantly more demanding engine operating conditions and thus, emit more pollutants by orders of magnitude compared to known cycles like NEDC. Here, especially the reduction of NOx is a specific technical challenge, as it needs to compromise also with reduction targets on carbon dioxide. The fulfilment of both emission limits requires a widening of the focus from an isolated engine or exhaust aftertreatment view to a system engineering view involving all hardware and software domains of the vehicle.
The investigation of RDE by means of simulation enormously increases the complexity of standard vehicle performance and fuel consumption models. The transient nature of real driving specifically requires transient models of the entire powertrain, including engine, cooling and driveline. Additionally, a comprehensive exhaust gas aftertreatment model is key. It needs to comply with the requirements of various types of catalysts and particulate filters (PNA, DOC, SCR; DPF, SDPF, LNT, …) in a highly flexible manner. Transient driving also requires appropriate controls (i.e. air path control, fuel path control, exhaust gas control) that either can be tackled by software models of the xCU or by linking the model to a hardware xCU on a Hardware in the Loop (HiL) bench. The latter approach additionally challenges the numerical solution procedure of the virtual vehicle model as hard real-time constrains need to be fulfilled.
This work presents a real-time capable vehicle modelling framework for office and HiL based simulation in the concept phase. Based on a use-case of a diesel engine powered passenger car, all essential modelling areas (engine, combustion, pollutant formation, exhaust gas aftertreatment, …) are discussed in detail and verification simulations of selected component models are presented. The base parameterization of the model including a simplifying control strategy makes it suitable for the simulation of engine outlet and tailpipe emissions in the concept phase. A variation matrix of key design and operation parameters (catalyst sizing and arrangement, i.e. injection timings, …) is defined and drive-cycle simulations are performed for a list of randomly assembled, though RDE compliant, driving manoeuvres. Key performance indicators such as emissions and fuel consumption are compared in their overall number and also in their distribution over the engine operating map. The HiL compliance of the model is presented by time measurements of an open loop model on an RT node.
Johann Krammer, Anton Nahtigal
AVL LIST GmbH
Symposium on International Automotive Technology 2019