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 results showed that there was a net deposition of particles on the catalyst during the first minutes of the cold start followed by a release at a later time that was related to the catalyst light-off time. The size distribution was shown to change between the inlet and outlet of the catalyst during this cold start period. These tests were carried out with preconditioning the previous day at idle and at high power. This gave two initial catalyst conditions -saturated with hydrocarbons and covered in soot (idle preconditioning) and relatively empty adsorber and soot free catalyst. The results showed that both preconditioning modes of the catalyst gave deposition on the catalyst. The size distribution changes across the catalyst were different for the two preconditioning techniques.
The cold start part of diesel test cycles is becoming more important and, since oxidation catalysts are a major part of the emissions control in diesel passenger cars, their performance is of significance. This work shows that in terms of particulate emissions there is a complex performance under cold start conditions.