Fuel Vapor Canister Purge Using Ejector and Vacuum Reservoir
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Solution Overview
Problem
In boosted engines, the increased path length for fuel vapor purging results in hydrocarbon transport delays and limited vacuum generation, leading to engine hesitation and insufficient purging, especially during conditions with reduced intake vacuum.
Innovation Solution
A method involving a pressurized gas from an engine coolant degas bottle coupled to an ejector in the fuel vapor canister vent line, enabling purging independent of engine intake pressure by drawing atmospheric air through the canister, even during low vacuum conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If fuel vapor purging uses the traditional intake manifold vacuum path in boosted engines, then the system can operate with existing components, but the increased path length causes hydrocarbon transport delays and engine hesitation
Solution Approach 1:
The purging system is segmented into two independent pathways: a traditional vacuum-driven path for non-boosted conditions and a new pressure-driven path for boosted conditions. This segmentation allows each pathway to be optimized for its specific operating condition, eliminating transport delays in boosted mode by using a direct routing that bypasses the compressor and intercooler.
Solution Approach 2:
A vacuum reservoir is introduced as an intermediary component that stores vacuum pressure during non-boosted conditions and releases it during boosted conditions to drive canister purging. This mediator enables purging independence from real-time intake manifold vacuum, solving the transport delay problem by providing a stored pressure source that can act immediately when needed.
2Adaptability or versatility
If an ejector is used to generate vacuum during boosted conditions, then purging can be enabled, but the vacuum generation is limited by ejector choke flow
Solution Approach 1:
The system dynamically switches between different vacuum sources based on engine operating conditions: using intake manifold vacuum during non-boosted conditions and transitioning to vacuum reservoir discharge during boosted conditions. This dynamic adaptation allows the system to maintain optimal fresh air flow through the canister across all operating modes, overcoming the choke flow limitation of static ejector designs.
Solution Approach 2:
The system changes the pressure parameter by storing vacuum pressure in the vacuum reservoir during low-demand conditions and releasing it during high-demand boosted conditions. This parameter change enables the system to deliver sufficient fresh air flow through the canister during boost when the ejector alone would be limited by choke flow.
3Device complexity
If canister purging relies on engine intake vacuum, then the system is simple to control, but purging cannot be executed when intake vacuum is below threshold
Solution Approach 1:
The vacuum reservoir is charged with vacuum pressure in advance during non-boosted conditions when intake vacuum is available. This preliminary action ensures that when boosted conditions occur and intake vacuum drops below the threshold needed for purging, the pre-charged reservoir can immediately provide the necessary vacuum pressure to enable continuous purging operation.
Solution Approach 2:
The system uses its own operating conditions to service itself: during non-boosted conditions, the engine's natural intake vacuum automatically charges the vacuum reservoir, and during boosted conditions, the stored vacuum in the reservoir automatically enables purging without requiring external intervention or complex control systems.
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 allows for effective purging of the fuel vapor canister during boosted and low-manifold vacuum conditions, reducing emissions and minimizing engine stalling events by maintaining a consistent purge path length and increasing purge efficiency.
Implementation Method 1
An inlet of an ejector may be coupled to an engine intake upstream of a compressor via a first conduit and an outlet of the ejector may be coupled to an intake of the engine downstream of the compressor via a second conduit. Motive fluid through the ejector provides a vacuum at an ejector suction inlet which is coupled to the fuel vapor canister to draw purge air through the fuel vapor canister during boosted operation.
Data Source
AI summary
A method for an engine is presented, wherein during a first condition, pressurized gas from an engine coolant degas bottle to an ejector positioned in a vent line coupled to a fuel vapor canister; and the contents of the fuel vapor canister are purged to an engine intake. The ejector may draw atmospheric air into the fuel vapor canister, thus enabling purging of the fuel vapor canister even when an engine intake vacuum is below a threshold. In this way, boosted engines and other engines configured to operate with reduced intake vacuum may execute canister purging events that are independent of engine intake pressure.