SCR Systems: Delphi SCR ammonia (NH3) sensor technology
The stringent standards that are set out in Euro 6/VI legislation for NOX emissions reduction will be followed by even stricter targets for 2020 when details of the EU’s Euro 7/VII regulations are announced. Manufacturers of vehicles, engines, and SCR systems are researching and developing systems and components which can improve performance and efficiency, to enable them to meet these standards.
New innovations in components are being designed continually as the industry gathers pace, and two of the most recent advances are detailed below.
Delphi SCR ammonia (NH3) sensor technology
Due for initial production in 2012, Delphi has developed an ammonia sensor for the automotive industry, which enables more efficient emissions control. The system allows the SCR (read also more here) to work at optimized NOX conversion rates, which in turn improves fuel efficiency.
The sensor dynamically measures the content of ammonia in emissions and the system can adapt the urea dosage accordingly. Some existing SCR technology use a timed urea dosing process; without accurate means of measurement and control excess and residual ammonia can escape via the exhaust stream. It is anticipated that part of the EU directives will relate to the control of ammonia slip from SCR systems, so the monitoring of ammonia levels will soon be an essential requirement.
The ammonia sensor is placed downstream of the SCR catalyst and NOX sensor; it detects the levels of ammonia in the exhaust stream over a range of 0-100ppm. The sensor converts the ammonia into an electrical signal that the electronic control system uses to control the urea solution dosage.
The ammonia sensor is the first technology that enables an SCR system to have a direct closed loop control system; allowing the optimisation of the urea dosage to be controlled by measurement of the emissions.
Future innovation and design
SCR systems have been developed and improved upon very quickly since the EU implemented their emissions strategy and the standards for the industry to comply with. To develop SCR systems to meet requirements of Euro 6/VI regulations, and systems that can be used beyond 2020, manufacturers will require more innovative designs to provide even greater efficiency.
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