Emission Reduction of a Stoichiometric Gasoline Direct Injection Engine 2005-01-3687
During the development of conventional PFI engines, WOT (Wide Open Throttle) performance tends to be sacrificed for exhaust emission reduction in order to meet the latest emissions regulations. To satisfy both power and emissions, a new V-6 engine employing stoichiometric gasoline direct injection, the 3GR-FSE, with variable intake and exhaust valve timing systems, was developed and meets the ULEV exhaust emission standard without sacrificing WOT performance. It is generally understood that THC emissions are reduced during warm-up through quick catalyst light-off by retarding ignition timing. However, the effect of this is limited by engine torque fluctuations. Under this warm-up condition, stratified charge combustion is known to significantly improve the engine torque fluctuation and enable more retard ignition timing. Furthermore, by using the variable exhaust valve-timing system, the internal EGR gas assists fuel spray atomization, increasing the expansion ratio to promote HC combustion in the chamber. As a result, THC emissions are reduced.