NOx Model Calibration for BS VI Application 2019-26-0050
KEYWORDS: EATS, SCR, LNT dew point, WLTC, NEDC, engine modes, DeNOx systems
Engineering challenge - Problem description
The challenging limits for NOx emission introduced in BS VI emission legislation demands high performance conversion techniques. EATS (Exhaust after treatment systems) such as LNT (Lean NOx Trap) and SCR (Selective Catalytic Reduction) can provide effective conversion of Engine – out NOx emissions. From the moment of engine start, these systems require reliable signal input of the upstream NOx sensor. The efficient use of such DeNOx systems demands earliest possible activation of the upstream NOx sensor. However, attainment of the sensor dew point delays this process. Data collected from the emission test cycles, WLTC and NEDC indicates the unavailability of NOx sensor from the beginning of the cycle. This makes the requirement of a NOx model inevitable.
The scope of this paper is to elucidate the calibration process through which a robust estimation of the NOx emissions can be made in different engine modes along with varying ambient conditions. This NOx model is capable of estimating the real time NOx emission using a map based approach in consideration of multiple factors such as coolant temperature, ambient air temperature and pressure. Initially, a set of reference maps is generated for the required engine modes by performing mappings at the dynamometer. With sophisticated climatic dynamometers and modern calibration tools and techniques, it is possible to introduce a robust calibration of the model which the DeNOx system can rely upon.
This paper contains data collected from various measurements performed at emission/ non emission dynamometers, cold temperature and hot temperature test trips, altitude test trips. The robustness of the NOx model calibration can be validated by testing across vehicle variants and thereby taking into account the measurement drift across NOx sensors.