With the conventional injection strategy (CIS), noise reduction always goes along with a decreased premixed and an increased diffusion-controlled combustion part. This results in increased soot emissions. With double spatial injection strategy (DSIS), noise reduction can be achieved at the same level or even better than with CIS, so, DSIS is an appropriate alternative for the CIS. The presented results of the first experimental investigations with DSIS show a high potential for simultaneous soot and NOx reduction. The better mixture homogenization and improved oxygen utilization in the combustion chamber gives the possibility to apply high exhaust gas recirculation (EGR) rates without strong soot penalty. In addition, high EGR rates have a positive influence on noise emissions due to a decreased rate of heat release. With DSIS, the fuel quantity of the main injection is decreased by approximately a half compared to the injection with advanced split injection strategy (ASIS). The rate of heat release of the DSIS injection in the inner bowl is reduced strongly compared to main injection because the inner bowl is not optimized for a very good mixture formation as the omega bowl is. A substantial part of soot emissions is emitted because soot oxidation processes stop in regions of cylinder wall due to heat loss. With DSIS, reduced heat losses in the centre if the combustion chamber enable a longer and better soot oxidation compared to soot formed in the outer areas of the combustion chamber. So, soot oxidation process is extended both temporally and spatially. However, this new double spatial injection strategy enables much more opportunities for the application of a Diesel engines with direct injection, particularly concerning the exhaust aftertreatment. Future legislative emission restrictions such as Euro 6 will decrease limiting values for pollutant emissions. Soot and NOx emission reduction can also be achieved by well established exhaust aftertreatment solutions like a diesel particulate filter (DPF) for soot emissions or a DeNOx or SCR catalytic converter for NOx emissions. But, these systems are expensive and require additional application effort. Furthermore, systems like a DPF or DeNOx catalytic converter have a need for regeneration periods with a significantly increased fuel consumption. So, an in-cylinder solution for reducing NOx and soot would be favourable. With the possibility of emission reduction with DSIS, it is possible to omit the exhaust aftertreatment system for either soot or NOx.
NOx reduction by a new split injection strategy
2012
10 Seiten, 16 Bilder, 1 Tabelle, 8 Quellen
Conference paper
Storage medium
English
Noise and Emissions Reduction by Second Injection in Diesel PCCI Combustion with Split Injection
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