Modular HD – Exhaust gas treatment system with autarcic thermal management for high urban NOx conversion

Autoren

Klaus Schrewe, Dr. Bernd Maurer, Dr.-Ing. Christoph Menne, Ingo Zirkwa, HJS Emission Technology GmbH & Co. KG

Jahr

2019

Zusammenfassung

With the European Directive 2008/50 EC on Ambient Air Quality, the European Commission is pursuing the goal of ensuring that the annual average ambient air quality limit of 40 μg/m3 for NO₂, which has been in force since 2010, is ensured. Compliance with this directive is a major challenge for many municipalities and federal states.
Especially in urban areas, NO₂ limit values are often exceeded. Transient low-load operation with low exhaust temperatures and sometimes high NO_X raw emissions during the acceleration phases also pose special challenges for the complex exhaust aftertreatment systems of buses and commercial vehicles. With regards to the problem of Real Driving Emissions (RDE) in the urban environment and in light of the expected future exhaust emission legislation, HJS has further developed the well-known SCRT technology and added important technology components.
In addition to highly efficient catalytic converters and optimized NH₃ mixture preparation, the focus was placed on autonomous thermal management technologies and corresponding control algorithms in order to achieve very high NO_X conversion rates even in demanding urban operation. The first application of this modular HJS heavy duty exhaust aftertreatment platform is in city buses.
Diesel particulate filters are well established to reduce particulate emissions from diesel engines and are being used in most new applications already.
The guidelines for retrofitting diesel buses as part of the "Sofortprogramm Saubere Luft 2017 – 2020" have defined emission limits and testing boundary conditions which even go beyond the IUC regulations for Euro VI buses, especially in inner-city operation.
In order to meet the emission requirements of this directive in real city bus operation, a thermal management is required in addition to an optimised EURO VI exhaust gas aftertreatment with DOC, DPF and SCR in order to reliable operate the SCR system in an efficiency-optimised temperature window even at the lowest speed profiles.
The modular heavy duty exhaust aftertreatment system with independent thermal management presented in this paper aims to significantly increase the efficiency of the SCR system in transient inner-city operation. The exhaust gas temperature in the low load range is raised by up to 50 °C for this purpose. Central elements for this are a quick, electrically operated exhaust flap along with an electrically heated diesel oxidation catalyst.
By the exhaust flap, the exhaust back pressure is slightly increased in certain low load driving situations. The electrically heated catalyst arranged in front of the particulate filter increases the exhaust gas temperature and the engine load via the additional load on the alternator.
The HJS aftertreatment control unit ACU processes the measured values such as NO_X,
temperatures, pressures, exhaust gas mass flow, status of the electrical system, etc. and
controls the actuators in such a way that the best possible NOX reduction is achieved
with minimum fuel consumption penalty. The system is also fully diagnosable.
The system contributes immediately to the reduction of NOX emissions and thus to improved
air quality in urban areas. The modular concept and the smart CAN bus and
sensor-based control also qualifies the HJS system for other commercial vehicle applications
beyond city bus applications and EURO VI legislation. For the first time, engine
heating measures can be enhanced by engine operating point independent thermal management
measures to help reliably meet future RDE-focused legislation in critical city
operation.
In the following, the performance of the system will be demonstrated as an example for
retrofitting a city bus application.

Mitglieder-Login