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Previous work on the transient storage of particulate in diesel exhaust systems (SAE 2000-01-0508) was carried out mainly at conditions where storage in the exhaust would dominate the process. The test involved a preconditioning of the engine the previous day with about 4 hours of engine idling. This ensured that the exhaust had a significant level of deposits. The following day low power cold starts were investigated and the movement of particulate between the two silencer boxes was determined as well as the net blow out of deposited particulate. Continuing deposition if particulate was also shown even in the presence of net blow out. The present work extends this previous work to higher power blow out conditions. Also investigated was the preconditioning of the engine at high power the previous day so that the exhaust was in a much cleaner condition. The previous tests were then repeated.

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.