LUXEMBOURG – Delphi Automotive has developed a NOx control for diesel engines with a new selective catalytic reduction (SCR) system that improves the performance, packaging and long-term reliability of the system as well as reduces vehicle CO2 emissions by up to 1g/km over any comparable system.
By injecting aqueous urea solution into a SCR system at up to four times the pressure of any previous system, which allows the catalyst to be close coupled to the engine, Delphi has solved many of the issues associated with other SCR systems.
A modular architecture
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 20 bar directly into the exhaust stream. The solution is supplied to the injector by a low pressure pump within the Urea Delivery Module (UDM) in the remote urea tank. The third element of the system is the electronics and software used to control the dosing subsystem.
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 unique 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 entire life of the system. The superior performance of the Delphi doser allows exhaust designers to move the SCR catalyst closer to the engine which in turn saves on CO2 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.
Additionally, 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.
Simplified installation into the vehicle
The modular architecture of the main system elements simplifies installation into the vehicle and offers flexibility to individual vehicle manufacturers. Depending upon customer preference, Delphi can provide either a Dosing Control Unit, a simple Heater Control Module or just the software and electrical interface specifications to control the dosing sub-system. Where required, Delphi can also provide system services to specify and calibrate the dosing sub-system. 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 first production application of the Delphi SCR system is scheduled for introduction in 2012.