Evaporative Canister Adsorbent Gradient for Low Purge DBL
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current evaporative emission control systems face challenges in reducing diurnal breathing loss (DBL) emissions, especially when purge air levels are low or when adsorbents in the canister are purged less frequently, such as in hybrid vehicles, resulting in emissions exceeding regulatory limits.
Innovation Solution
The implementation of an evaporative emission control system with a 'step-down' gradient in adsorption capacity as vapor flows from an initial adsorbent volume to subsequent adsorbent volumes, and a 'step-up' gradient as air flows in the opposite direction, utilizing adsorbent volumes with specific incremental adsorption capacities and structures to facilitate uniform air and vapor flow distribution, thereby reducing DBL emissions to below 20 mg even with low purge volumes.
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 fuel/air mixture management becomes complicated and tailpipe emissions are adversely affected
Solution Approach 1:
The canister is divided into multiple zones with different adsorbent materials having distinct adsorption capacities. The first zone contains adsorbent with higher adsorption capacity while the second zone contains adsorbent with lower adsorption capacity, creating a gradient that optimizes purge efficiency without requiring excessive purge gas volume.
Solution Approach 2:
Different regions of the canister are assigned different adsorbent properties tailored to their specific functions. The upstream zone uses high-capacity adsorbent for initial vapor capture, while the downstream zone uses lower-capacity adsorbent that facilitates easier desorption during purge, creating localized optimization throughout the system.
2Object-generated harmful factors
If the canister cross-sectional area on the vent-side is reduced to increase purge air intensity, then residual hydrocarbon heel is reduced, but excessive flow restriction is imposed on the canister
Solution Approach 1:
The canister cross-sectional area varies along the flow path, with the vent-side zone having a smaller cross-section to concentrate purge air flow and enhance desorption intensity where needed, while the fuel-side zone maintains a larger cross-section to minimize overall flow restriction and facilitate vapor intake during engine operation.
3Ease of operation
If purge air volume is kept low to simplify mixture management, then fuel/air mixture control is easier, but DBL emissions exceed regulatory limits especially in hybrid vehicles with infrequent purging
Solution Approach 1:
The adsorbent materials are selected and positioned to create a gradient in adsorption capacity parameters along the flow path. This parameter variation enables the system to achieve effective heel removal with reduced purge volumes by optimizing the energy required for desorption at different zones, making the system effective even with limited purge opportunities in hybrid vehicles.
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 approach effectively reduces DBL emissions to within regulatory limits of 20 mg or less, even under low purge conditions, by optimizing the adsorption and desorption processes in the canister system, ensuring compliance with stringent emission standards.
Implementation Method 1
the fuel vapor enters the canister through a fuel vapor inlet of the canister and diffuses into the adsorbent volume where the fuel vapor is adsorbed in temporary storage
Implementation Method 2
The purge air flows through the adsorbent volume inside the canister and desorbs the fuel vapor adsorbed on the adsorbent volume
Implementation Method 3
the fuel vapor enters the canister through a fuel vapor inlet of the canister and diffuses into the adsorbent volume
Data Source
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. 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 BETP butane loading step.