The CRT® system
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The CRT® system is the most widely used DPF system in the world and is a patented Johnson Matthey technology. It comprises an oxidation catalyst followed by a DPF. The principle of its operation is shown below.
The oxidation catalyst removes CO and HC and oxidises some of the NO in the exhaust gasses to NO2. This NO2 then reacts with the PM trapped in the filter, producing NO and CO2 and cleaning the filter.
CRT® system performance
This chart shows the emissions reduction achieved by a CRT® system fitted to a Euro 1 truck engine over the ESC 13-mode cycle. The conversions shown are typical of the performance of a CRT® system.
Operating conditions
The conditions normally required for reliable CRT® performance are:
- a significant proportion (~50%) of the operating time with an exhaust temperature >250°C,
- a ratio of NOx:PM in the exhaust gases 20:1 or greater,
- the use of fuel with a maximum sulphur content of 50ppm.
These conditions are conditional on each other and exact requirements depend on the system and the application. If these conditions cannot be met, a CCRT® system should be considered instead. Johnson Matthey has many years of experience of specifying CRT® systems for diverse applications and is able to advise on which system is most suited to individual applications.
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