Statistical uncertainty in automotive emissions testing

Automotive exhaust emission testing according to legislated procedures and driving cycles is a routine process today in the United States, Europe and SE Asia. In practice, the selection of catalytic converters and the general design of exhaust aftertreatment systems are mainly aimed at the attainmen t of the legislated emissions limits with a reasonable safety margin. Howev er, during the system optimization process, the catalyst and/or exhaust sys tem manufacturer screens a large number of catalysts with a significant num ber of system design variations. In this process, certain levels of statist ical uncertainty are present and must be seriously taken into account as st ricter emissions standards are addressed and the safety margins become lean er. A methodology is developed and presented in this paper that is able to determine confidence levels in the attainment of specific emissions limits. This methodology combines results from experimental assessment of the dist ributions of engine-out emissions and catalyst activity by employing a prev iously developed and extensively validated model of a diesel oxidation cata lyst. In this way, the emissions control system optimization is substantial ly aided and the required experimental effort is considerably reduced.