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Compared with in-line 4-cylinder engines, V-6 engines show a slower rise in exhaust gas temperature, requiring a longer time for catalysts to become active, and they also emit higher levels of engine-out emissions. In this study, The combination of a new type of catalyst, and optimized ignition timing and air-fuel ratio control achieved quicker catalyst light-off. Additionally, engine-out emissions were substantially reduced by using a swirl control valve to strengthen in-cylinder gas flow, adopting electronically controlled exhaust gas recirculation (EGR), and reducing the crevice volume by decreasing the top land height of the pistons. A vehicle incorporating these emission reduction technologies reduced the emission level through the first phase of the Federal Test Procedure (FTP) by 60-70% compared with the Tier 1 vehicle.

This paper describes new technologies for achieving exhaust emission levels much below the SULEV standards in California, which are the most stringent among the currently proposed regulations in the world. Catalyst light-off time, for example, has been significantly reduced through the adoption of a catalyst substrate with an ultra-thin wall thickness of 2 mil and a catalyst coating specifically designed for quicker light-off. A highly-efficient HC trap system has been realized by combining a two-stage HC trap design with an improved HC trap catalyst. The cold-start HC emission level has been greatly reduced by an electronically actuated swirl control valve with a high-speed starter. Further, an improved Air Fuel Ratio (AFR) control method has achieved much higher catalyst HC and NOx conversion efficiency.