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A trap oxidiser system using exhaust gas throttling as main regeneration system, coupled to a by-pass control of ceramic temperature, was installed on five experimental buses of the Athens bus fleet. Cerium Naphthenate was also used as fuel additive at different concentrations, in order to ensure safe and reliable regeneration at relatively low temperatures. The behaviour of the systems was constantly monitored through data loggers, during regular on-road operation. In order to examine the performance of all available materials, parallel tests were carried out using wall flow ceramics of different configurations and foam type ceramic monoliths. The paper presents the evaluation of the results obtained after 9 months of systems operation, with an accumulated minimum of 45,000 km of useful life per system.

A test protocol, allowing for the evaluation of diesel particulate filters of different materials and of different sizes, located at various distances from the engine was developed. A total of 13 filter configurations were tested on a Euro I naturally aspirated diesel light duty truck with a fully passive trap system, utilizing only cerium-based additive in the fuel. It was proved that regeneration under constant urban driving conditions was always possible, at an exhaust gas temperature at the trap inlet in the range of 250 - 350°C. On a gravimetric basis, the efficiency of the traps tested concerning PM was in the order of 45 - 80% over the NEDC, depending on trap material and location along the exhaust pipe and reflecting the specific composition of the PM generated by the vehicle. No major effect on gaseous emissions (HC, NOx and CO) was observed.

The first two of a series of traps retrofitted on a pilot fleet of 110 buses of the Athens Bus Corporation were removed for examination after 100,000 km of revenue service. These buses were gradually equipped with the ELBO Trap Oxidiser since the beginning of 1989 and are constantly operated on Cerium based fuel additive. The physical properties and the chemical composition of filters and ash residues were analysed by the filter manufacturers and the fuel additive producer. The results have shown that after two years of operation the filter material remained intact and the ash deposits (consisting mainly of CeO2) exhibit a limited interaction with the cordierite. More than 94% of these deposits are filtered by the monoliths and could be removed to a large extent with the application of conventional methods.

A light duty truck with a naturally aspirated engine was equipped with a DPF (changing the exhaust pipe and eliminating the muffler) and operated on fuel doped with a cerium based additive in various concentrations. Tests were carried out on chassis dynamometer using the European urban cycle, but also under city driving conditions with maximum speeds up to 50 km/h and exhaust gas temperature up to 300°C. Under these conditions, it was observed that filter regeneration was always possible at relatively high particulate accumulation in the filter, while the effect on fuel consumption (as measured over the emission test cycles) was not detectable, compared to baseline data of the vehicle. Change in driving conditions from slow urban to highway with highly loaded trap led to spontaneous trap regeneration at higher temperatures, without effect on fuel consumption. This paper documents the operation of a fully passive DPF system for diesel light duty vehicles.