Vapor Canister Heater for Evaporative Emissions Systems

Automotive evaporative emissions systems use a charcoal canister to store evaporative hydrocarbon emissions. These stored vapors are later purged and burned during engine operation. Under certain conditions the engine cannot completely purge the canister of the stored fuel vapors, which results in a decreased vapor storage capacity in the canister. A self-regulating PTC (Positive Temperature Coefficient) heater has been developed to warm the purge air as it enters the canister, in order to provide thermal energy for increased release of the vapors from charcoal sites. This paper describes the construction and operation of the vapor canister heater as it relates to improved evaporative emission system performance.