Fuel Vapor Canister Reverse Purging via Pre-Heating
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Solution Overview
Problem
Conventional methods for heating fuel vapor canisters after an engine-off event to facilitate reverse purging are limited, especially for hybrid vehicles that do not rely on external power sources, and can result in inefficient desorption due to insufficient vacuum creation in the fuel tank, leading to excess fuel vapor escape and compromised emissions quality.
Innovation Solution
A method that heats the fuel vapor canister before an imminent engine-off event, based on diurnal temperature changes, to create a vacuum in the fuel tank, allowing for efficient reverse purging by sealing the tank and initiating purging when the pressure reaches a threshold, and maintaining heating until the canister load is reduced.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional passive purging is operated during engine-off state without heating assistance, then energy consumption is reduced, but desorption efficiency is insufficient leading to excess fuel vapor escape
Solution Approach 1:
The canister heater is activated before the engine-off state to pre-heat the adsorbent material. This preliminary heating ensures that when reverse purging occurs during the engine-off state, the adsorbent has sufficient temperature to effectively desorb fuel vapors, thereby resolving the contradiction between maintaining desorption efficiency and reducing energy consumption during passive purging.
2Productivity
If canister heater is activated during engine-off state for reverse purging, then desorption efficiency is improved, but control strategy complexity increases
Solution Approach 1:
The control system monitors canister load, ambient temperature, and engine operating state to dynamically determine when to activate the canister heater for reverse purging. This feedback-based control ensures the heater is activated only under appropriate conditions (e.g., when canister load is high and ambient temperature is low), improving reverse purging efficiency while avoiding unnecessary complexity by using simple conditional logic based on readily available sensor data.
3Stress or pressure
If fuel tank is not sealed before reverse purging, then vacuum creation is insufficient, but system simplicity is maintained
Solution Approach 1:
The fuel tank is sealed by closing the variable bleed valve before initiating reverse purging during the engine-off state. This preliminary sealing action creates the necessary vacuum pressure differential that drives the reverse purging process, allowing fuel vapors to be drawn from the canister back into the fuel tank. The sealing action is a simple valve operation that does not add significant system complexity while effectively creating the required vacuum conditions.
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 enables more efficient desorption during reverse purging, broadens the applicability of canister heating strategies beyond extended range hybrid vehicles, and extends the longevity of the fuel vapor canister, potentially allowing for smaller, lighter, and more cost-effective EVAP system designs.
Implementation Method 1
heating the fuel vapor canister before an imminent engine-off event
Implementation Method 2
enables more efficient desorption during reverse purging
Implementation Method 3
As fuel vapors in the tank cool and condense back into liquid during the cool-down portion of the diurnal ambient temperature cycle, a vacuum may be formed in the fuel tank
Data Source
AI summary
Methods and systems are provided for reverse purging of a fuel vapor canister of an engine. In one example, a method may include heating a fuel vapor canister, sealing a fuel tank in order to generate a vacuum in the fuel tank, and in response to the pressure in the fuel tank reaching a target vacuum, initiating reverse purging of the fuel vapor canister.