Ambient temperature effect on automotive exhaust emissions: FTP and ECE test cycle responses

Over the past decades, the automotive industry has managed to successfully meet the demands set by the continuous and worldwide progress in exhaust emission legislation. This has, to a great extent, been possible by employing catalytic exhaust aftertreatment. The growing use of advanced emission control has now brought an increasing number of vehicles using such technology also to the areas of cold climate like the Nordic countries. However, the low ambient temperature and cold operating conditions have been found to increase the emissions and to derate the performance of the catalyst system. This has been the case, because the guidelines for the design are mainly set by the legislation, in which low ambient temperature conditions have so far not been considered in test procedures. This paper discusses the emissions performance of current technology vehicles in low ambient temperature conditions. Both the U.S. FTP75 and the ECE test procedure, now comprising the ECE15 and the EUDC driving schedules, have been used to assess the response of vehicles and their emission control systems. Four fleets of cars, altogether over 20 vehicles, have been tested at subzero temperatures. The results show clearly the negative effect of low ambient temperature. Furthermore, they illustrate how dependent the emission output is on the test procedure and driving schedule applied.