The compliance of future emission standards is in need of new technologies and a significantly increased development effort for new combustion processes.Copyright: RWTH Aachen | VKA
Currently, different technologies are under development and in series production to evolve Diesel engines to have an extremely clean and efficient drive. Besides the possibility of a partially very complex subsequent cleaning of the exhaust gas, the combustion process optimization is operated to ensure as low as possible engine-out emissions levels. Most of the time, the combination of exhaust-gas aftertreatment and a combustion that is optimized to the case of application lead to a compliance of the emission limit value. Essentially, this deals with soot and nitrogen oxide emissions, which are independent of the course of combustion. Possibilities of influencing the course of combustion arise on the air side via boost pressure, charge motion, and exhaust gas recirculation rate as well as on the fuel side via fuel injection.
For instance, there is still a substantial potential with injection to optimize Diesel-engine combustion. Modern injection systems such as the Common-Rail system already offer a high flexibility concerning injection point, pressure, and number of injections. Furthermore, a trend has emerged to use higher injection pressure to be able to inject more fuel at full load without increasing the spray-hole diameter. The latter would subsequently lead to a worsening of the fuel carburation and to disadvantages concerning the emission level.
Other variabilities, such as a variable geometry turbine geometry at the turbocharger (VGT), a variable valve gear timing (VVT), or a variable compression ratio (VCR-Pleuelconrod), initiate further optimization possibilities. Similarly, there are many different concepts with exhaust-gas aftertreatment to reach the necessary emissions. Besides a separate optimization of combustion and exhaust-gas aftertreatment, the cooperation of all used measures becomes increasingly important.
At the VKA, different research projects investigate Diesel-engine combustion and its exhaust-gas aftertreatment. This is done on either engine test benches, or component test benches, such as a laboratory gas test benches to characterize catalysts, or via simulation.