This paper compares and discusses the impact of conventional and improved start strategies on the design of the exhaust aftertreatment system.
It is recognised that hardware measures on the exhaust side will not be sufficient if Volvo's 5 and 6 cylinder engines are to fulfil SULEV emission levels, assuming passive three way systems only. A new start strategy, providing an excessive heat profile combined with low engine out hydrocarbon emissions, was therefore developed. Temperature profiles, raw emissions and mass flow obtained with the Lean Start Calibration will be shown for the 5 and 6 cylinder engines, both naturally aspirated as turbo.
The remaining part of the paper presents a brief history of the exhaust aftertreatment design modifications for Volvo's 5 cylinder N/A engine fulfilling LEV, ULEV I, ULEV II and PZEV emission levels respectively. The impact of the new start strategy on the cold start performance will be shown. The results will demonstrate the potential of an under floor only system for ULEV II emission levels and a close coupled cascade plus under floor system for PZEV emission levels when the new start strategy is applied. The effect of design parameters such as substrate choice, catalyst volume, … as well as the effect of ageing (both temperature and poisoning), on the cold start and the hot phase emissions will be discussed.