Multi-Layer EVAP Canister Layout for Low DBL Emissions
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Solution Overview
Problem
Existing evaporative emission control systems struggle to maintain low diurnal breathing loss (DBL) emissions, especially under low purge conditions or in hybrid vehicles where the adsorbents are purged less frequently.
Innovation Solution
The evaporative emission control system incorporates an initial fuel-side adsorbent volume with a high incremental adsorption capacity and multiple vent-side adsorbent volumes with lower incremental adsorption capacities, optimized to achieve low DBL emissions even with reduced purge air.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the volume of purge gas is significantly increased to enhance desorption of residue hydrocarbon heel, then DBL emissions are reduced, but management of fuel/air mixture becomes complicated and tailpipe emissions are adversely affected
Solution Approach 1:
The patent changes the physical-chemical parameters of the adsorbent material by using a multi-layer configuration with different adsorbents having distinct properties. The first layer uses a high-capacity adsorbent for maximum vapor uptake, while subsequent layers use adsorbents with progressively lower capacity but better selectivity or desorption characteristics. This parameter differentiation allows effective DBL control without requiring excessive purge gas volumes, thereby avoiding complications in fuel/air mixture management.
2Object-generated harmful factors
If the cross-sectional area of the canister is reduced to increase purge air intensity, then residual hydrocarbon heel is reduced, but flow restriction becomes excessive
Solution Approach 1:
The patent applies local quality by creating zones with different adsorbent properties within the canister. The first adsorbent layer is positioned to handle the bulk of vapor adsorption with high capacity, while subsequent layers are positioned to refine the purification process. This spatial differentiation of adsorbent qualities allows the system to achieve low residual heel without requiring a reduced cross-sectional area, thereby maintaining adequate flow characteristics and avoiding excessive energy loss.
3Object-generated harmful factors
If heating is applied to purge air or adsorbent volume to increase purge efficiency, then DBL emissions are reduced, but control system complexity increases and safety concerns arise
Solution Approach 1:
The patent employs adsorbent materials that naturally facilitate desorption through their inherent properties without requiring external heating. The multi-layer adsorbent system is designed so that the subsequent layers with lower capacity but appropriate thermal or chemical characteristics enable passive desorption during the purge cycle. This self-service approach eliminates the need for active heating systems, thereby reducing control system complexity and avoiding associated safety concerns while still achieving effective DBL emission control.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration effectively reduces DBL emissions to within the regulatory limits of 20 mg or less, even under low purge conditions, thereby meeting stringent emission standards.
Implementation Method 1
the fuel vapor from the fuel tank enters the canister through a fuel vapor inlet of the canister and diffuses into the adsorbent volume where it is adsorbed in temporary storage
Implementation Method 2
ambient air is drawn into the canister system through the vent port of the canister. The purge air flows through the adsorbent volume inside the canister and desorbs the fuel vapor adsorbed on the adsorbent volume
Data Source
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AI summary
An evaporative emission control canister system comprises an initial adsorbent volume having an effective incremental adsorption capacity at 25°C of greater than 35 grams n-butane/L between vapor concentration of 5 vol% and 50 vol% n-butane, and at least one subsequent adsorbent volume having an effective incremental adsorption capacity at 25°C of less than 35 grams n-butane/L between vapor concentration of 5 vol % and 50 vol % n-butane, an effective butane working capacity (BWC) of less than 3 g/dL, and a g-total BWC of between 2 grams and 6 grams. The evaporative emission control canister system has a two-day diurnal breathing loss (DBL) emissions of no more than 20 mg at no more than 210 liters of purge applied after the 40 g/hr butane loading step.