Understanding the chemistry and control of GDI cold-start emissions and the role of HC-Traps

Melanie  DeBusk, NTRC-Oak Ridge National Laboratory

As emission regulations continue to become increasingly more stringent for passenger vehicles, the reduction of the cold-start emissions has become the major focus.  A GDI vehicle’s three-way catalyst (TWC) can reduce most of the gaseous emissions, hydrocarbons (HC), CO and NOx, once reaching its light-off temperature, the temperature at which it is hot enough for active conversion.  However, over the U.S. urban drive cycle for emissions (FTP-75), it takes a TWC about 250s to reach 500°C, at which point it can provide active emissions control.  To meet future emissions regulations, emissions control during those first 250s are expected to be required through the development of catalysts active at lower temperatures and/or methods to trap the emissions during cold-starts. The increased emissions during a vehicle cold-start are largely attributed to cold cylinder walls, oil and catalysts, making engine studies ideal for understanding how cold start exhaust HC speciation compares to the exhaust HC composition from a GDI engine after it is warmed-up.  Detailed speciation during the first 250s of the FTP-75’s cold-start will be presented from a study on two MY2018 GDI vehicles with  2.7L turbocharged and a 5.3L naturally aspirated engines.  The impact of a HC-trap catalyst on these emissions, including changes in the hydrocarbon-specific speciation, will also be explored.