Boosted Gasoline Engine Exhaust Temperature Control via EGR and Enrichment
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Solution Overview
Problem
High engine load in boosted gasoline engines leads to undesirably high exhaust temperatures, which can accelerate material aging in engine systems and result in fuel economy losses when attempting to reduce these temperatures through enrichment strategies.
Innovation Solution
Aggressive exhaust-gas recirculation (EGR) is applied during high-load conditions, combined with enrichment of the air-fuel mixture, to dilute the intake air charge to different levels based on operating conditions, thereby protecting exhaust-system components without significant fuel economy loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the air-fuel mixture is enriched during high-load conditions to reduce exhaust temperatures, then exhaust temperature is reduced and component aging is slowed, but fuel economy deteriorates due to excess fuel providing no power
Solution Approach 1:
The patent combines two strategies—exhaust-gas recirculation (EGR) and air-fuel mixture enrichment—that were previously used separately or in opposition. By merging EGR (which dilutes intake charge to reduce combustion temperature) with controlled enrichment (which provides evaporative cooling), the system achieves exhaust temperature reduction while recovering some of the fuel that would otherwise be wasted, thereby improving fuel economy compared to enrichment alone
Solution Approach 2:
The system dynamically adjusts multiple parameters including air-fuel ratio, EGR rate, and boost pressure based on operating conditions. During high-load transients, the control system modifies these parameters in coordination—enriching the mixture when needed while simultaneously increasing EGR to maintain combustion stability and reduce exhaust temperature without excessive fuel consumption
2Temperature
If aggressive exhaust-gas recirculation is applied during high-load conditions to reduce exhaust temperature, then exhaust temperature is reduced and component protection is improved, but combustion stability may deteriorate due to increased dilution
Solution Approach 1:
The patent applies different EGR strategies to different operating conditions and engine zones. High-pressure EGR is used primarily during high-load conditions where temperature reduction is critical, while low-pressure EGR provides baseline dilution control. The system locally optimizes the dilution approach by selecting which EGR system to use based on the specific operating point, maintaining combustion stability while achieving temperature reduction where needed
Solution Approach 2:
The control system continuously monitors combustion stability indicators and exhaust temperature, adjusting EGR rate and air-fuel ratio in real-time. When combustion stability begins to deteriorate due to excessive dilution, the system reduces EGR or enriches the mixture to restore stability, creating a feedback loop that maintains both temperature control and combustion reliability
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 exhaust temperatures and maintains fuel economy by utilizing EGR in conjunction with enrichment, extending the life of exhaust-system components and improving combustion stability during high-load transients.
Implementation Method 1
diluting an intake air charge of the engine to a first level of dilution when operating at a stoichiometric air-to-fuel ratio
Implementation Method 2
Above the stoichiometric ratio, liquid fuel injected into an engine cylinder does not contribute to combustion, but to evaporative cooling of the combustion gasses therein
Implementation Method 3
In addition, the excess fuel may be reformed endothermically in the cylinder, providing further cooling
Data Source
AI summary
A method for operating a boosted gasoline engine. The method includes diluting an intake air charge of the engine to a first level of dilution when operating at a stoichiometric air-to-fuel ratio. The method also includes, in response to a condition of excessive exhaust temperature downstream of the engine, diluting the intake air charge of the engine to a second, greater level of dilution while operating at an enriched air-to-fuel ratio.