Metallic substances, usually added to fuel as organic compounds are, as fuel additives proven to curtail particulate emissions from diesel engines and, as fuel borne catalysts (FBC), to promote regeneration of particle traps. During combustion, these substances form catalytic metal oxides and exit the combustion chamber as ultra-fine solid clusters in the mobility diameter range of 5-30 nm.
Particles of this size and composition have a health impact and should not enter the respiratory air. FBC should therefore only be used together with particle traps, which can efficiently collect these metal oxide particles at all operating conditions. This and other requirements are stipulated in the VERT suitability tests for particle trap systems. The approval procedure includes a particle size-specific analysis to verify trap penetration in trace quantities. The results of these suitability tests are reported together with methods, for sample extraction and analysis, to detect trace quantities of metallic particulate matter in fine resolution impactors.
Results of an offroad utility vehicle engine in ISO 8178 cycle are shown as an example. The results confirm that modern particle filters can trap these ultrafine particles with an efficiency >99%.
Further research is needed to investigate whether operation conditions may exist, particularly during regeneration of fully loaded traps at high space velocity conditions, where noticeably higher emissions occur.
The results substantiate the necessity to very carefully test particle trap systems with FBC regeneration, and verify their secondary emissions.