SCR catalytic converters

SCR catalytic converters are used to reduce nitrogen oxide emissions (_NOx = NO + _NO2) using the so-called SCR process. SCR stands for Selective Catalytic Reductionand describes a process in which the harmful nitrogen oxides are selectively, i.e. specifically converted on a suitable catalytic converter. HJS began developing this technology back in the mid-1990s.

Functionality

The exhaust gas from diesel engines usually contains excess oxygen (_O2). In order to reduce nitrogen oxides under these conditions, a selective reducing agent is required which converts the nitrogen oxides specifically to nitrogen (_N2) and water (_H2O). The reducing agent used here is an aqueous solution of urea (trade name ^AdBlue®), which decomposes in the exhaust gas and forms the actually active reducing agent ammonia (_NH3).

The classic SCR catalytic converter contains _V2O5 as an active component. However, due to the volatility of this active component at very high temperatures, such as those that can occur during particulate filter regeneration, zeolite-based catalysts have become increasingly popular in recent years.

In addition to the activity of the catalytic converter, the performance of the SCR system depends on the optimum preparation of the ^AdBlue® reducing agent, which must be injected into the exhaust system as a spray in such a way that no deposits are formed. In addition, the released ammonia must be ideally distributed to the SCR catalytic converter.

In order to cope with these tasks, HJS has developed various application-specific solutions that take into account the respective operating conditions, if necessary under independent control.

Area of application

SCR systems are used in both passenger cars and commercial vehicles and, in combination with a particulate filter as an SCRT® system, are the leading system architecture for vehicles of the Euro VI/6 or EPA 2010 generation when it comes to really clean exhaust gases. Furthermore, it will also be standard for many “non-road” diesel engines, i.e. for use in construction machinery as well as agricultural and forestry machinery, from 2019 at the latest. This technology is also used for stationary engines or rail and marine applications. HJS SCRT® systems are available both for original equipment applications and for retrofitting.