Abstract
Recent environmental standards concerning suspended particulate matter (SPM) are continuously becoming stricter. A plan to require diesel particulate filters (DPF) on inner city diesel vehicles was demanded by the environmental council of Tokyo in March 2000. Reduction of diesel exhaust particles (DEP) has become an extremely important social problem for such reason.
However, performance and durability for practical use of current DPF systems is unsatisfactory. In addition, a reasonable evaluation method for the reduction effect of particulates is not yet established. On this account, considering the hasty market introduction, the potential for confusion is evident. In addition, current DPFs fail to trap a disproportionate amount of nanoparticles (Dp<50nm), and improvement of the trap efficiency becomes an important problem. Furthermore, performance considerations demand a reduction in the engine backpressure increase due to DPF installation.
However, particulate matter (PM) displacement volume and particle size distribution of DPF have hardly been examined in transient driving conditions. In particular, a tendency for change in the ultra fine particle size (Dp<100nm) distribution with an installed DPF is not well understood. Yet, it is known that the influence on the human body of such ultra fine particles is large. PM reduction technology and establishment of an evaluation method are necessary for practical use of DPF to solve these problems.
In order to evaluate the reduction of PM by DPF we measured exhaust gas and PM by Japan 13-mode cycle for heavy duty diesel vehicles (D13), European Stationary Cycle (ESC) and various transient cycles: U.S. transient cycle (UST), European transient cycle (ETC), Japan Automobile Research Institute (JARI) mode cycle, and World-wide Heavy Duty Cycle (WHDC). The size distribution of diesel exhaust particles was measured using an electric low-pressure impactor (ELPI). The PM volume in steady cycle tests, D13 and ESC cycles was larger than in transient cycle tests when DPF was installed. It is necessary to estimate the amount of accumulated PM in the DPF to evaluate the PM reduction rate correctly. On the other hand, in the case of installed DPF, the particle those measurement results of particle number distribution by ELPI, generally showed a median diameter of trapped PM of less than 62nm.