Automotive SCR systems are dimensioned to reduce NOx efficiently in normal driving conditions. In markets such as North America and Europe, extreme winter conditions are common over a period of many weeks where temperatures are usually below DEF (Diesel Exhaust Fluid) freezing temperatures at −11°C (12°F).
In previous studies and applications, DEF was heated in the tank in a dedicated pot or alternatively by a standardized central heater. Due to the local character of these heating solutions, it was not possible to thaw the full tank volume.
The objective of this study is to demonstrate how to significantly improve performance of the SCR system in cold weather conditions for passenger car, light commercial vehicles and SUV applications. The performance improvement is demonstrated by sustainability testing showing how much of the full tank content can be thawed and made available for injection in the exhaust system.
Based on maximum average dosing rates of 250 g/h, external temperatures down to −40°C and depending on the tank shape the heater is designed to optimize tank heating performance. Once the prototype is made, tests are performed to confirm the real system performance in these extreme conditions. Test results show the capability of the heating system to reach more than 90% of the tank volume and to ensure that liquid DEF is available for injection, even at the maximum average dosing rate of 250 g/h.