The Application of Two Closely Coupled DPFs as the After-treatment System

In this study, the application of two closely coupled Diesel Particle Filters (DPFs), composed of an assistant DPF and a main standard honeycomb DPF, was investigated. A series of tests were carried out on a light-duty common-rail Euro 4 diesel engine and the emissions were measured and compared with those when a standard DOC+DPF system was used for the after-treatment. Replacing the DOC with an assisting DPF (ADPF) showed significant advantages in the reduction of particles, which had a direct impact in reducing the soot loading rate of the main DPF by up to 30%. Its oxidation characteristics not only showed equivalent exhaust-conversion efficiency, which concern the regulated gaseous emissions (CO and HC) under most engine conditions, but also continuously regenerated the soot it trapped. The impacts on the particle size and distributions were investigated, based on the new regulations on particle number limits; as well as the increased back pressure which is an unavoidable compromise. The overall performance of this DPF+DPF strategy showed great potential to be adopted in the future, Not only can this cope with tighter emissions regulations but it also has great cost benefits as main DPF's size and weight can be reduced. It also encourages more options for other cheaper materials as less soot is collected.