While fuel efficiency has to be improved, future Diesel engine emission standards will further restrict vehicle emissions, particularly of nitrogen oxides. Increased in-cylinder filling is recognized as a key factor in addressing this issue, which calls for advanced design of air and exhaust gas recirculation circuits and high cooling capabilities.
As one possible solution, this paper presents a 2-stage boosting breathing architecture, specially dedicated to improving the trade-off between emissions and fuel consumption instead of seeking to improve specific power on a large family vehicle equipped with a 1.6-liter Diesel engine. In order to do it, turbocharger matching was specifically optimized to minimize engine-out NOx emissions at part-load and consumption under common driving conditions.
Engine speed and load were analyzed on the European driving cycle. The key operating points and associated upper boundary for NOx emission were identified. Then, automated single-cylinder engine tests were performed using the design of experiment method in order to characterize engine responses and to identify the corresponding in-cylinder filling targets.
Defining low full-load targets, turbo matching was undertaken to satisfy this performance requirements with the best charging capacity at part-load. Following a 0D air path simulation study based on manufacturer maps, two turbochargers were chosen.
Afterwards, an engine model was developed using the IFP-Engine library in the LMS Imagine.Lab AMESim simulation tool. Phenomenological combustion modeling was used and an advanced breathing architecture fully reproduced.
The physical modeling offered a means of checking that the in-cylinder filling targets could be achieved and of comparing the fuel consumption for different configurations. Lastly, transient simulations were performed to estimate the dynamic response of the engine in a vehicle situation.