SCR System and Performance Innovation
The Euro 6/VI regulations concerning greenhouse gas emissions from vehicles present manufacturers with the challenge of reducing several different gases using several different technologies incorporated into the same exhaust system. The reduction of NOX emissions alongside the reduction of CO2 has been a particular challenge for diesel engine manufacturers, and this has accelerated the advances in selective catalytic reduction (SCR) technology to meet NOX emission standards.
The Euro VI legislation due to take effect in 2014 requires an 80% reduction in NOX emissions compared with the Euro V standard. It is also expected that there will be a limit set for ammonia slip to control the amount of ammonia released from an SCR system. Several manufacturers are developing systems and components that aim to achieve such high levels of efficiency.
Delphi SCR dosing system
Delphi Automotive has developed an SCR system that improves performance and reliability of the system, as well as reducing NOX and CO2 emissions. The new system, due to be introduced in 2012, injects aqueous urea solution into the SCR system at up to four times the pressure of previous systems, and reduces CO2 by up to 1g/km when compared with similar systems.
The system is made up of three components. The SCR doser, which is an injector with high pressure pump, injects the urea solution directly into the exhaust at a pressure of 20 bar. The urea solution is fed to the doser by a low pressure pump situated in the Urea Delivery module (UDM). The whole process is controlled by the electronics and software used to manage the system.
Rather than use a timed injector opening, the Delphi system uses a positive displacement solenoid pump, which delivers accurate measured quantities of urea solution regardless of the supply pressure.
Haldor Topsoe’s retrofit SCR system
Haldor Topsoe has developed an innovative sensor based urea SCR system that can be retrofitted to any existing diesel engine to reduce NOX emissions. Installation and operation of the system is simple as no modification to the engine is required.
The system has a high NOX conversion rate of between 70% and 90%, unburned hydrocarbons are reduced by 80-90%, and particulate mass is reduced by 20-40%. The retrofit system uses Adblue urea solution, and requires a refill tank to be carried on the vehicle.
The sensors measure NOX emissions, the exhaust flow, and the temperature of the catalyst. Advanced control algorithms calculate the exact amount of solution to inject into the exhaust system. A digital dosing pump is used to dose the required amount of urea, which is mixed with air and injected into the exhaust by high pressure nozzle.
Advances in SCR systems and technology are in rapid development as manufacturers look at all avenues to improve performance and efficiency of their systems with EU directives and Euro 6/VI emissions strategies looming on the horizon. In the next article we will look at some of the developments in components which can help to improve efficiency and reliability.
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