Combustion Chamber Surface Roughness for Engine Knock Reduction
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Solution Overview
Problem
Internal combustion engines experience engine knocking due to high intake air temperatures, which are exacerbated by convective heat transfer from the combustion chamber walls, and existing mirror surface coatings do not effectively manage this issue.
Innovation Solution
The engine incorporates a combination of mirror and rough surface regions on various components such as the cylinder, cylinder head, piston, and valves to control convective heat transfer, minimizing temperature rise during the intake stroke and promoting cooling during the compression stroke by optimizing airflow and heat exchange.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the flow velocity of the intake air in the combustion chamber is increased to accelerate convective heat transfer, then heat transfer efficiency is improved, but engine knocking is more likely to occur due to higher intake air temperature
Solution Approach 1:
The invention applies different surface roughness characteristics to different regions of the combustion chamber walls. Mirror surface regions (Ra ≤ 0.3 μm) are positioned in areas where intake air flows at high velocity during the intake stroke to minimize convective heat transfer and prevent temperature rise that would cause knocking. Rough surface regions (Ra ≥ 0.3 μm) are positioned in areas where compressed air contacts the walls during the compression stroke to promote convective heat transfer and cool the air, preventing knocking while maintaining heat transfer efficiency.
2Loss of energy
If the wall surface of the combustion chamber is formed as a mirror surface to reduce convective heat transfer, then cooling loss is minimized, but the temperature of the intake air is increased and engine knocking is more likely to occur
Solution Approach 1:
The invention divides the combustion chamber wall surface into mirror surface regions and rough surface regions based on the flow characteristics and thermal requirements of different areas. Mirror surfaces are applied in regions where minimizing heat transfer is critical during intake, while rough surfaces are applied in regions where enhancing heat transfer is critical during compression, thus resolving the contradiction between minimizing cooling loss and preventing knocking.
Solution Approach 2:
The combustion chamber wall surface is segmented into functionally distinct regions with different surface treatments. This segmentation allows the wall to perform dual functions: minimizing heat transfer in certain areas during intake stroke while maximizing heat transfer in other areas during compression stroke, thereby preventing knocking without excessive cooling loss.
3Loss of energy
If a mirror surface is used to reduce radiation heat transfer from combustion gas to the wall, then cooling loss is minimized, but convective heat transfer from intake air to the wall is prevented, increasing intake air temperature and causing knocking
Solution Approach 1:
The invention applies mirror surface treatment selectively in regions where radiation heat transfer from combustion gas is the dominant heat transfer mechanism, while applying rough surface treatment in regions where convective heat transfer from intake air is the dominant mechanism. This local differentiation allows the wall surface to optimize for radiation reflection where needed while promoting convection where needed, resolving the contradiction between minimizing cooling loss and preventing knocking.
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 reduces the temperature of intake air, thereby enhancing anti-knocking performance by minimizing heat transfer during intake and promoting efficient cooling during compression, allowing for advanced ignition timing without engine knocking.
Implementation Method 1
convective heat transfer between the intake air and the mirror surface region of the wall structural components of the combustion chamber
Implementation Method 2
convective heat transfer between the intake air and the rough surface region of the wall structural components of the combustion chamber
Data Source
AI summary
In an internal combustion engine provided with a combustion chamber defined by an inner circumferential surface of a cylinder, an end surface of a cylinder head facing the cylinder, a crown surface of a piston, an inner surface of an intake valve, and an inner surface of an exhaust valve, for the purpose of improving the anti-knocking performance of the engine, the inner circumferential surface of the cylinder, the end surface of the cylinder head, the crown surface of the piston, the inner surface of the intake valve and the inner surface of the exhaust valve include a mirror surface region formed as a mirror surface having an arithmetic average roughness of 0.3 μm or less, and a rough surface region formed as a rough surface having an arithmetic average roughness of 0.3 μm or more.