Carbon Canister-Based Vapor Management System to Reduce Cold Start Hydrocarbon Emissions

摘要

Engine out (feedgas) emissions control during cold start operations has been a major technical challenge since mandated LEV/ULEV/SULEV/PZEV regulation compliance. Cold start emissions contribute to more than 85% of total emissions in a FTP test. Unburned hydrocarbons are mostly generated during cold starts due to a rich air/fuel ratio strategy. Cold intake and cylinder wall surfaces do not provide a quick vaporization bed for the rich fuel, therefore un-vaporized and unburned fuel result in excessive tailpipe emissions. Utilizing fuel vapor during cold starts reduces the hydrocarbon (HC) emissions level and minimizes the transient fuel effect process. A vapor management system must function to control the air-to-fuel ratio of the intake charge during "cold starts," idle, and drive-away, or until catalyst lights off to a desired level. Additionally, vapor fuelling can provide solutions to the inherent problems of "cold fuel enrichment," "wall wetting," "lost-fuel," and "mixture preparation," as well as, open up beneficial opportunities for lean air-fuel ratio cold starts. A vapor management control system consisting of a carbon canister vapor source, supplying a traditional induction system augmented with additional subsystems in a preferred configuration, has been designed and tested, and the results presented in this paper. A major reduction in HC emissions over liquid port injection (PFI) is achieved.