Anodic Oxidation Coating for Combustion Chamber Thermal Management
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Solution Overview
Problem
Conventional heat-insulating ceramic coatings for internal combustion engine combustion chambers have low thermal conductivity and high heat capacity, leading to reduced intake efficiency, knocking, and inadequate pressure and stress relaxation during combustion.
Innovation Solution
An anodic oxidation coating film with a specific microstructure featuring bonding and nonbonding regions, including voids at triple points, is formed on the combustion chamber walls, providing low thermal conductivity and heat capacity while allowing for pressure and stress relaxation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a heat-insulating ceramic coating film with low thermal conductivity is formed on the combustion chamber wall, then thermal losses are reduced, but heat capacity increases causing reduced intake efficiency and knocking
Solution Approach 1:
The patent applies a porous anodic oxidation coating film with controlled porosity (30-70%) on the combustion chamber wall. The porous structure provides low thermal conductivity for heat insulation while the controlled pore distribution and size (0.1-10 μm) prevent excessive heat capacity accumulation, thereby reducing thermal losses without causing knocking or reducing intake efficiency
Solution Approach 2:
The patent uses a composite structure consisting of a metallic base material (aluminum or aluminum alloy) and an anodic oxidation coating film layer. This composite provides both the structural strength of the metal and the heat-insulating properties of the oxide coating, achieving optimal balance between thermal insulation and heat capacity management
2Loss of energy
If a coating film with low thermal conductivity is formed on the combustion chamber wall, then thermal losses are reduced, but the coating film cannot withstand expansion pressure and injection pressure during combustion
Solution Approach 1:
The porous anodic oxidation coating film with controlled porosity (30-70%) and pore size (0.1-10 μm) provides both heat insulation and pressure resistance. The porous structure reduces thermal conductivity while the interconnected pores can accommodate and relax the expansion pressure and injection pressure during combustion, preventing coating failure
Solution Approach 2:
The patent optimizes specific parameters of the coating film including porosity (30-70%), pore size (0.1-10 μm), and film thickness (10-100 μm) to achieve the right balance between heat insulation performance and mechanical strength to withstand combustion pressures
3Loss of energy
If a coating film with low thermal conductivity is formed on the combustion chamber wall, then thermal losses are reduced, but the coating film cannot relax repetitive stresses from thermal expansion and shrinkage
Solution Approach 1:
The porous anodic oxidation coating film with controlled porosity (30-70%) provides stress relaxation capability. The porous structure allows the coating to expand and contract with thermal cycling, absorbing repetitive thermal stresses and preventing coating delamination or cracking
Solution Approach 2:
The composite structure of metallic base material and anodic oxidation coating film provides differential thermal expansion characteristics that help relax thermal stresses. The coating layer acts as a stress buffer that accommodates thermal expansion and shrinkage cycles
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
The coating film reduces thermal losses, improves fuel consumption by up to 5%, increases exhaust gas temperature, and enhances NOx purification by shortening the warm-up time of the NOx reduction catalyst.
Implementation Method 1
forming an anode by immersing all or a portion of the wall in an acidic electrolytic bath, forming a cathode in the acidic electrolytic bath, and then applying between the two electrodes a voltage adjusted to have a maximum value in the range from 130 to 200 V, and performing electrolysis at a heat removal rate adjusted to have a maximum value in the range from 1.6 to 2.4 cal/s/cm2
Implementation Method 2
an anodic oxidation coating film which has a structure provided with a bonding region in which each of hollow cells forming the coating film is bonded to the adjacent hollow cells, and a nonbonding region in which three or more adjacent hollow cells are not bonded to each other
Data Source
AI summary
An internal combustion engine in which an anodic oxidation coating film is formed on all or a portion of a wall that faces a combustion chamber, wherein the anodic oxidation coating film has a structure that is provided with a bonding region in which each of hollow cells forming the coating film is bonded to the adjacent hollow cells, and a nonbonding region in which three or more adjacent hollow cells are not bonded to each other, and wherein a porosity of the anodic oxidation coating film is determined by a first void present in the hollow cell and a second void that forms the nonbonding region.