Fuel Vapor Canister Purging and Sensor Diagnosis
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Solution Overview
Problem
Vehicle evaporative emission systems face challenges in thoroughly purging fuel vapors, particularly heavy ends, from the fuel vapor canister, leading to bleed emissions and inefficient energy use, with existing methods like hydrocarbon sensors and electrical heating posing reliability and power consumption issues.
Innovation Solution
A method involving the activation of a canister heating element within the fuel vapor canister to promote desorption of hydrocarbon vapors, where the canister is sealed initially to heat and then vented to route vapors into a vent line for monitoring by a hydrocarbon sensor, allowing for the diagnosis of both the heating element and sensor functionality while conserving energy by selectively purging light and heavy ends.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electrical heating is applied to the fuel vapor canister to promote desorption of hydrocarbon vapors, then desorption effectiveness is improved, but electrical power consumption increases
Solution Approach 1:
The system applies heating selectively based on canister temperature and hydrocarbon type. Light ends are purged using ambient temperature air flow, while heavy ends require targeted heating. This local quality approach ensures heating is applied only where and when necessary, improving desorption effectiveness for heavy ends without unnecessarily consuming electrical power for light ends purging.
Solution Approach 2:
The system changes the temperature parameter dynamically based on the purging phase. During light ends purging, the canister remains at ambient temperature. During heavy ends purging, the heating element activates to raise the canister temperature. This parameter change strategy optimizes the balance between desorption effectiveness and power consumption by matching temperature conditions to the specific hydrocarbon being purged.
2Device complexity
If the hydrocarbon sensor is positioned to detect vapors only at breakthrough, then device complexity is reduced, but measurement precision deteriorates as the sensor may never detect vapors until saturation occurs
Solution Approach 1:
The system performs preliminary purging actions to concentrate hydrocarbon vapors before the sensor needs to detect them. By actively purging the canister and routing vapors through the vent line where the sensor is positioned, the system ensures that sufficient vapor concentration reaches the sensor in advance, enabling reliable detection without requiring the sensor to be positioned at multiple locations or using complex detection algorithms.
3Device complexity
If the canister is purged using only intake manifold vacuum, then device complexity is minimized, but productivity decreases as heavy ends cannot be effectively desorbed
Solution Approach 1:
The purging process is segmented into two distinct phases: light ends purging using only intake manifold vacuum, and heavy ends purging that adds heating element activation. This segmentation allows the system to maintain simplicity for the majority of purging operations (light ends constitute most vapor volume) while adding targeted complexity only when needed for heavy ends, thereby improving overall purge completeness without excessively increasing device complexity.
Solution Approach 2:
The system applies partial heating action rather than continuous heating. The heating element is activated only during heavy ends purging phases when intake manifold vacuum alone is insufficient. This partial action approach ensures complete purging of all hydrocarbon types while avoiding excessive energy consumption that would result from continuous heating, thus improving productivity without disproportionate increase in energy use.
4Reliability
If the canister heater is activated continuously to ensure complete desorption, then purging completeness is improved, but energy waste increases
Solution Approach 1:
The heating element operates periodically rather than continuously, activated only during specific heavy ends purging phases when required for effective desorption. Between these periodic activations, the heating element remains off, allowing the system to achieve complete purging of heavy ends while avoiding continuous energy consumption. This periodic action pattern optimizes the balance between purging completeness and energy efficiency.
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 ensures thorough purging of both hydrocarbon light and heavy ends, conserves battery power, and reliably assesses the functioning of the canister heating element and hydrocarbon sensor, reducing undesired emissions and improving the fuel vapor canister's adsorption capacity.
Implementation Method 1
activation of a canister heating element within the fuel vapor canister to promote desorption of hydrocarbon vapors
Implementation Method 2
promote desorption of hydrocarbon vapors, where the canister is sealed initially to heat and then vented
Implementation Method 3
desorption of stored fuel vapors from the adsorbent material in the canister, regenerating the adsorbent material for further fuel vapor adsorption
Data Source
AI summary
Methods and systems are provided for conducting a canister purging operation and for rationalizing components of a vehicle evaporative emission system. In one example, after completion of a refueling event, a first fuel vapor canister purge operation is conducted to desorb hydrocarbon light ends from the fuel vapor canister, and subsequently the canister is heated to desorb hydrocarbon heavy ends from the canister, which are routed to a hydrocarbon sensor to rationalize the hydrocarbon sensor, before being purged to engine intake in a second purging operation. In this way, a fuel vapor storage canister may be thoroughly cleaned of hydrocarbon light ends and hydrocarbon heavy ends, while additionally indicating whether a canister heating element, and a hydrocarbon sensor positioned between the canister and atmosphere, are functioning as desired.