Particulate traps are mechanical devices for trapping soot, ash and mineral particles, to curtail emissions from Diesel engines. The filtration effectiveness of traps can be defined, independent of the pertinent engine, as a function of the particle size, space velocity and operating temperature. This method of assessment lowers cost of certifying traps for large-scale retrofitting projects [1,2].
VERT [3] is a joint project of several European environmental and occupational health agencies. The project established a trap-verification protocol that adapts industrial filtration standards [4] to include the influence of soot burden and trap regeneration phenomena. Moreover, it verifies possible catalytic effects from coating substrates and deposited catalytic active material from engine wear or fuel/ lubricant additives.
This verification test is performed for one single trap, out of a family of traps to be certified, on a representative Diesel engine under all conditions expected during operation (clean and loaded at different volume flows and temperatures and during regeneration). It supplies information on solid-particle size-specific filtration characteristics and secondary emissions. This supplementary data is decisive in judging the overall health-effect quality.
Impaction and diffusion constitute the physical processes that cause trapping particles within a filter medium. Only such particles are of relevance that are solid while transiting the filter matrix. Accordingly, the appropriate particle measuring method ought to be used for this purpose.