SCR Systems

22 July 2010

Delphi Automotive announced a new selective catalytic reduction (SCR) urea dosing system for light-duty vehicles. The system injects urea solution into the SCR system at 2 MPa—up to four times the pressure in previous systems—which provides better mixing with exhaust gas and allows the catalyst to be close-coupled to the engine. Since the need for active catalyst warm-up strategies (such as through rapid engine warm up) is reduced, the system brings an added benefit of CO2 emission reduction of up to 1 g/km, according to Delphi.

The system consists of three basic modules:

  • The SCR doser—an injector with integrated high pressure pump—is mounted in the exhaust line just ahead of the SCR catalyst and injects the urea solution at 2 MPa directly into the exhaust stream.
  • The urea delivery module (UDM) in the remote urea tank includes a low pressure pump that supplies the solution to the injector.
  • The electronics and software module is used to control the dosing subsystem.

Delphi emphasized a number of advantages of their new system:

  • The high pressure of the dosing injector, combined with an innovative insulation arrangement, prevents the urea solution from boiling within the doser, allowing its tip to be directly exposed to the hot exhaust. This architecture puts more energy into the urea spray which requires less mixing energy from the exhaust and eliminates deposit formation at the nozzle tip. It also ensures consistent spray performance over the life of the system. The superior performance of the doser allows exhaust designers to move the SCR catalyst closer to the engine, which in turn saves on CO2—compared to engines with alternative SCR dosing systems—as catalyst heating and light-off strategies can be reduced.
  • Unlike alternative systems that use timed injector opening, the Delphi system uses a positive displacement solenoid pump that delivers an accurate, metered quantity of urea through the injector, regardless of supply pressure, throughout the lifetime of the system.
  • The urea delivery module (UDM) can be customized to integrate the functions of urea level sensing, lifetime filtration, heating for defrosting in winter and a delivery pump, packaging conveniently into the base of the tank. The delivery pump is only required to pressurise the urea solution to prevent boiling in the feed lines.

Currently applicable to passenger cars and light commercial vehicles, the technology is also being developed with higher flows to suit medium- and heavy-duty diesels. The system is intended for Euro 6, Tier 2 Bin 5 and corresponding Japanese regulations. The first production application of the Delphi SCR system is scheduled for 2012.

Source: Delphi