Carbon Canister and Evaporative Emission Control System (EVAP) Modeling

Jonathan  Brown, Gamma Technologies

The carbon canister is the center piece of the evaporative emission control system, also referred to as the EVAP system for OBD2.  The carbon canister uses activated carbon to store hydrocarbon vapor when the concentration is high, and to purge the hydrocarbon vapor when the concentration is low.  Historically the carbon canister was simply purged to the intake manifold during idle and part load operation when there was sufficient vacuum pressure.  When the purge valve opened the fresh air would flow into and through the canister purging the fuel vapor to be burned in the cylinder.  Now with the increasing number of turbocharged gasoline direct injection (GDI) engines, the intake manifold is often in a boosted state, requiring a more complex purge valve system and control strategy for determining when and where to purge the canister.

In addition, CARB LEV III is calling for zero-fuel hydrocarbon emissions for zero emission vehicle (ZEV) designation of 100% by 2022.  For hybrid electric vehicle (HEV) applications with an on-board generator there are potential trade-off decisions to be made about the fuel tank and the EVAP system.

With these control system complexities, emissions requirements, and different design scenarios, engineers need the ability to use a model to quickly and accurately predict the fuel vapor storage level of the carbon canister for different operating conditions, predict the purge valve behavior, and design and optimize the control strategy for the EVAP system.

This presentation will focus on how to implement a carbon canister model in a commercial simulation software tool (GT-SUITE).  Reaction rate input, and fuel vapor loading and purging results will be presented in detail.  A brief overview of other EVAP system component models, and integration with the engine model will be presented as well.

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