Influence of Three-Way Catalyst on Gaseous and Particulate Matter Emissions During Gasoline Direct Injection Engine Cold-start

The development of gasoline direct injection (GDI) engines has provided a strong alternative to port fuel injection engines as they offer increased power output and better fuel economy and carbon dioxide emissions. However, particulate matter (PM) emission reduction from GDI still remains a challenge that needs to be addressed in order to fulfil the increasingly stricter environmental regulations. A large number of the total particulate emissions during driving cycles are produced during the engine cold-start. Therefore, controlling PM during cold-start events will significantly reduce the final PM output. This research work provides an understanding of PM characterisation from a 2 l four-cylinder GDI engine during cold-start. Gaseous emissions including hydrocarbon (HC) speciation studies are also carried out pre-and post-a Euro 6 compliant three-way catalyst (TWC). In addition, particulate size distribution and total particulate number were recorded for the first 280 seconds after the engine cold-start. Large concentrations of carbon monoxide, propane, acetaldehyde, formaldehyde, ethanol, toluene and ethylene were emitted during the first 70-90 seconds from the engine start. Gaseous emissions were reduced on the catalyst at temperatures higher than 290 degrees C, with the catalyst reaching almost 100% removal efficiency at 350 degrees C. The effect of the TWC on PM emissions has been analysed for the different PM diameter ranges. A reduction of particles smaller than 20 nm was observed as well as a reduction in the accumulation mode. In order to understand the nature of the particles emitted during cold-start, transmission electron microscope (TEM) grids were used for particulate collection at the engine start and after 80 seconds and 140 seconds of engine operation. A peak of 1.4 x 10(8) particles was produced at the engine start and this steadily reduced to 3 x 10(7) in 50 seconds. The TEM micrographs showed solid particles with similar fractal-like shapes.