Carbon Canister-Based Vapor Management System to Reduce Cold-Start Hydrocarbon Emissions 2005-01-3866
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.