EXPERIMENTAL STUDY ON THE EMISSION CHARACTERISTICS OF HEAVY-DUTY DIESEL ENGINE WITH COMBINATION SYSTEM OF DOC/DPF/SCR

An emission characteristic of heavy-duty diesel engine was experimental studied using the combination system of diesel oxidation catalyst (DOC)/diesel particulate filter (DPF)/selective catalytic reduction catalyst (SCR) to expect the engine would achieve CN-VI standard in this paper. The research was focused on the effects on the particulate matter emissions including particle mass (PM) and nitrogenous compounds emissions including NOx, nitrogen dioxide (NO2)/NOx" The results showed that the upstream DOC and DPF reduced the PM by 92.7% ant ESC test cycle and 87.06% at ETC test cycle, respectively. While the downstream SCR brought about an average decrease of 82.51% NOx" Both PM and NOx emission factors based on this retrofit were lower than CN-V limits (ESC) at medium and high loads. The combination after-treatment of DOC+DPF+SCR was proved a feasible and effective project in terms of reducing particulate emissions and NOx simultaneously for in-use engine. There is no obvious influence on the pollutants conversion efficiency with the different arrangement order of the SCR and DOC+DPF system. The passive regeneration of DPF can be fully achieved by placing the DOC+DPF ahead of the SCR system due to the sufficient amount of NO2 in the exhaust which can be utilized for PM oxidation, and also in this case the hydrothermal aging effect on the SCR catalyst could be reduced owing to the lower of the inlet temperature. The backpressure of the combination after-treatment can be less than 28 kPa through the application of ceramic-based DPF and optimal design of the packaging structure.