Petrol Engine Low-Pressure EGR Circuit Knock Control
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Solution Overview
Problem
Turbocharged gasoline engines face issues with knocking during full load conditions, leading to potential engine damage, and existing solutions to mitigate this, such as enriching the fuel mixture or delaying ignition, result in increased fuel consumption and pollution.
Innovation Solution
Incorporating an exhaust gas recirculation circuit with a cooler connected to the intake circuit upstream of the compressor, which reintroduces cooled exhaust gases to delay knocking and increase ignition advance, while maintaining stoichiometric fuel proportions to reduce fuel consumption and emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the fuel mixture is enriched or ignition timing is retarded to prevent knocking, then knocking is limited, but fuel consumption increases and catalytic converter efficiency decreases
Solution Approach 1:
Cooled exhaust gases are introduced as an intermediary substance into the intake air stream. These exhaust gases act as a heat sink that absorbs excess heat from the air-fuel mixture, lowering the temperature and preventing auto-ignition without requiring fuel enrichment or ignition timing retardation, thus maintaining both knocking prevention and fuel efficiency
Solution Approach 2:
The temperature parameter of the intake air is actively modified by mixing in cooled exhaust gases. This temperature reduction changes the thermal state of the mixture, increasing its resistance to knocking while maintaining stoichiometric fuel proportions, thereby resolving the contradiction between reliability and energy consumption
2Reliability
If cooled exhaust gases are introduced into the intake system, then knocking resistance increases, but the complexity of the system increases
Solution Approach 1:
The exhaust gas recirculation system performs multiple functions simultaneously: it cools the intake charge to prevent knocking, recycles unburned hydrocarbons and carbon monoxide back to the combustion chamber for complete oxidation, and reduces nitrogen oxide formation. This multi-functionality justifies the added system complexity by delivering multiple benefits from a single integrated system
Solution Approach 2:
The system uses the engine's own exhaust gases, which are already present in the system, as the cooling medium. The exhaust gases that would otherwise be wasted are redirected back to the intake system, creating a self-contained loop that utilizes existing resources rather than requiring external cooling systems
3Reliability
If exhaust gases are recirculated at high temperatures, then knock resistance increases, but damage to turbine and catalytic converter components increases
Solution Approach 1:
The exhaust gases are cooled in advance before being introduced to the intake system. The cooler unit pre-cools the recirculated gases to a temperature that provides sufficient knock resistance when mixed with intake air, while simultaneously reducing the thermal load on downstream components such as the turbine and catalytic converter, preventing overheating and extending component life
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 limits knocking, increases engine torque, reduces fuel consumption, and lowers exhaust gas temperatures, minimizing catalyst and turbine component stress, and decreases nitrogen oxide emissions.
Implementation Method 1
a cooler connected to the intake circuit and an exhaust gas recirculation circuit which is connected to the exhaust circuit downstream of the turbine and is connected to the intake circuit upstream of the compressor
Implementation Method 2
the reintroduced cooled exhaust gases play no role in combustion but act as a heat trap, notably limiting the formation of auto-ignition zones in the combustion chamber mixture
Data Source
Figure 1
AI summary
Internal combustion petrol engine comprising an engine block (2) connected to an intake circuit (3) including a compressor (6) and an exhaust circuit (4) including a turbine (13) which drives the compressor, the internal combustion engine including an exhaust gas recirculation circuit (11) which is connected to the exhaust circuit downstream of the turbine and is connected to the intake circuit upstream of the compressor, the recirculation circuit comprising a cooler. Method of managing such an engine.