Search Results

This work is part of a larger programme to investigate the storage at low power conditions and release at high power conditions in real diesel engine exhaust systems. The initial particle storage in the oxidation catalyst, followed by a release of particles a few minutes later, is explored, and the associated particle size distribution changes determined. A Ford 1.8L IDI Diesel Engine, Turbocharged and Intercooled (TCIC), and equipped with Exhaust Gas Recirculation (EGR), was used under high speed and high power conditions, both during cold start. The commercial close-coupled diesel oxidation catalyst had an associated hydrocarbon adsorber for cold start hydrocarbon control. The tests were carried out using a step cold start to a fixed low power output, typical of city driving. The ELPI particle size analyser was used together with constant temperature gravimetric filter based mass samples upstream and downstream of the catalyst.

The accumulation and release of particulate matter within the exhaust system of a modern light-duty diesel engine was studied during a step cold start to three steady state load conditions, idle, 10 and 15kW. Changes in particulate mass concentration through the various components of the exhaust system were dependent on the previous short-term history of the engine operation, and on the engine speed reached during cold start. Particulate matter was deposited within the oxidation catalyst when cold and in the downstream exhaust silencer at idle and low power conditions. Particulate matter was released from the first silencer at all three test conditions and this release exceeded the deposition in the downstream silencer and resulted in a net exhaust system particulate blowout, at all three test conditions. This was a large fraction of the tailpipe emissions at all three test conditions.

Diesel exhaust particle size distribution and total number concentration were measured at different positions along the exhaust system of a practical light-duty passenger car diesel engine. Continuous particle size measurements during the diesel cold start were made in 12 particle size ranges using the ELPI particle size analyser. Three engine speeds were studied using a step cold start procedure to the set load and speed condition. The exhaust system had an oxidation catalyst with hydrocarbon absorber and two silencers. Particle size distributions were determined upstream and downstream of the catalyst and the two silencers. There were considerable variations in the particle number and size distribution after the cold start. The catalyst was shown to act as a store for fine particles and there were further particle losses across the two silencers.