Die NOx – Abscheidung optimieren


Buses and commercial vehicles are retrofitted with the PURItech AdBlueTM injection to Euro 6 emission standard.

Exhaust gas purification significantly upgrades older diesel engines, serves mobility systems based on combustion engines, and promotes health through remarkably improved air.

High-quality exhaust gas cleaning

The PURINOX SCRTTM technology enables a NOx reduction of generally well over 90 percent. In the vast majority of operating conditions, no NOx emissions remain detectable during PEMS measurement runs. Due to the system’s excellent heat storage, even long pause times, during which the engine temperatures naturally drop, can be bridged. A subsequent heating of the exhaust gas or an additional injection of diesel into the exhaust tract is not necessary with this system.

Further pollutants in the air are hydrocarbons (HC) and carbon monoxide (CO) with values just below 100%.

The fine dust produced during the combustion of diesel fuel, measured in the number (PN) and mass (PM) of the particles, is also almost completely filtered. Of several hundred thousand ultra-fine particles that can be produced per cubic centimeter of displacement during a combustion process, up to 99.99% can be filtered out.

The PURItech air filters also indirectly free the air of ultra-fine particles from other sources, which can get past the engine air filter and enter the exhaust system via the engine.

The system is characterized by a comparatively very low exhaust counter-pressure. This reduces fuel consumption, extends filter maintenance intervals and helps the engine do its job with less effort.

The system’s modularity additionally increases the conditions for trouble-free operation. The particle filter is easy to clean and even the SCR catalyst should be exchangeable without having to replace the entire system, something which is generally not the case; this is an important contribution to investment security.

The filter cleaning system recommended by PURItech ensures that the ceramic elements used for filtration can be reused after cleaning for just as long as before the first cleaning. The shortening of the cleaning intervals via a filter that is not completely free of soot is excluded, as is damage to the ceramic through cleaning, which would partially render the filter ineffective.

Perfection in every detail

The PURInox system combines CRT (Continously Regeneration Trap) and SCR (Selective Catalytic Reduction) technology in a minimum amount of space.

The CRT® part of PURInox® consists of a specially optimized oxidation catalyst and a ceramic wall flow filter that absorbs fine dust and ultrafine particles to effectively reduce both particulate mass and number.

In the subsequent new AdBlueTM cyclone mixer, the filtered exhaust gas is enriched with an aqueous urea solution, which is carried in an extra tank in the bus. The special feature of the mixer concept is the precise definition of the air flows and the injection conditions of the AdBlueTM via a special nozzle. Both can be mapped very precisely in simulation calculations. Thus the perfect function is not achieved by constant testing on real components, but by simulation calculations – right up to the perfect mixing.

Another innovation at PURINOX is the extremely precise control of the AdBlueTM feeder. The control unit, specially developed with partners, combines on-board diagnostics (OBD), with which the system is completely actively monitored and protected, with a particularly precisely adjustable AdBlueTM dosage. This is another advantage of the chosen mixer principle. Depending on the condition of the system, exactly the amount of AdBlueTM that is currently required is injected. In this way, a little more AdBlueTM can be injected if necessary to ensure functional reliability and, on the other hand, “unnecessary” AdBlueTM consumption can be avoided. Random air flows, which are difficult to simulate, do not occur as disturbance variables of such an objective, independent of the temperature. All these advantages ultimately lead to the fact that the mixer section can be shortened, which slightly reduces weight and costs.

Finally, the enriched exhaust gas reaches the SCR catalyst, which is coated with up to seven chemical substances. Here the exhaust gas has a lot of space and time to produce harmless nitrogen and water vapor from NOx and AdBlueTM. The comparatively voluminous barrier catalyst ensures that no ammonia formed from AdBlue escapes from the system. The special catalysts also maximize the primary NO2 reduction.

Last but not least, the special integral insulation prevents the PURINOX system from losing its stored thermal energy in the oxidation filter, the diesel particulate filter and the catalytic converters, which would have a negative effect on the function at very cold temperatures and low load conditions.

Efficiency through modularity

As mentioned earlier, the CRT and SCR units have a modular design for replacement or more convenient maintenance. Service orientation plays an important role here.

Modularity was based on the idea of making it easy for the customer through offering a robust solution that always works. In order to avoid disadvantages resulting from the installation of such a SCRT system elsewhere, the design was based on the premise of the lowest possible exhaust counter-pressure. This may increase to a value recommended by the manufacturer during the life of the filter before uncontrolled and therefore undesirable results are achieved in exhaust gas recirculation. The clear objective was therefore to achieve long maintenance cycles when designing the individual components. PURINOX offers economic advantages where suppliers with smaller units sometimes reach the limits of economic efficiency.

Together PURINOX offers the most economical way to upgrade Euro 3, 4, 5 and EEV buses to Euro 6. About 15 buses can be upgraded at the price of a new diesel bus.