Measurement of regulated and unregulated emissions at low ambient temperature

Cold operating environment has many kinds of negative effects on the use of automobiles. Low ambient temperature degrades start-up performance and increases fuel consumption. Hence, the amount of harmful exhaust emissions is also elevated. In particular, high concentrations of carbon monoxide (CO) and unburned hydrocarbons (HC) are present. The continuously widening implementation of US-type emission regulations around the world has brought emission control technology based on the use of three-way catalyst (TWC) even to the Nordic countries having cold climate. Cold-start increases emissions from conventional cars, and especially the performance of TWC type of emission reduction has been shown to be quite susceptible to low ambient temperature. Therefore, an increasing emphasis has been set to the testing of exhaust emissions also at sub-normal temperatures, i.e. below the range of +20 …+30°C widely designated by the legislative procedures. Furthermore, US-EPA has recently formulated a forthcoming regulation comprising an additional low ambient temperature (20°F ≈ -7°C) test for CO emission along with the respective standard. The harmful impact of exhaust gases extend even beyond the toxic and other known health effects of the regulated components, that is CO, HC and NO_x (nitrogen oxides). Other poisonous compounds, although usually in very small quantities, have been detected from the exhausts. A cold-start may even have an increasing effect to the emission of these substances. Therefore, although yet unregulated, as many as possible of these compounds should be included into the analysis. Current methods for detecting this type of components are primarily based on ‘wet chemistry’. Therefore, they are very laborous and time consuming and, hence, allow no real-time analysis of transient phenomena to be performed. However, recent R&D efforts have made FTIR-technology, already widely and succesfully used in stack emission analysis, available also to the engine exhaust analysis applications. This enables even transient operating modes to be studied.