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This paper describes the second generation of the partial zero emission vehicle (P-ZEV) technology that was developed for use on the Nissan Sentra CA sedan sold in California.1,2 The second-generation engine has been adopted on a mass-produced model marketed in Japan. Besides continuing the super ultra low emission vehicle (SULEV) performance of the Sentra CA, the second-generation technology incorporates a compact, two-stage HC trap catalyst system. The system has been substantially reduced in size and cost as a result of improving the catalyst and the substrate and reducing the total catalyst volume by optimizing the control method. Moreover, the second-generation P-ZEV technology includes an electrically actuated continuously variable swirl control valve of the high-speed jet type, a high-response electrically actuated EGR valve and catalyst model control based on the use of an air-fuel ratio sensor.

It is projected that compliance with Japanese new exhaust emission regulations set to be enforced in 2000 year will be difficult for turbocharged engines with conventional technologies. This is mainly because of the delay in catalyst lightoff at engine start due to the lower exhaust gas temperature of turbocharged engines compared with that of their naturally aspirated counterparts. Compliance will be particularly difficult for V-6 engines on account of the large heat mass of the exhaust system, resulting in a slower temperature rise. Previously, improvement of hydrocarbon (HC) conversion rates following engine start depended solely on the low-temperature characteristic of the catalyst. The catalyst system described here adopts a completely new mechanism that traps HCs before the catalyst lights off and then desorbs them for conversion after the engine warms up.