Sealed Piston Cooling Gallery Using Bi-Sn Heat Transfer Alloy
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Solution Overview
Problem
Existing piston designs for internal combustion engines face challenges in efficiently managing high temperatures, particularly in the upper crown, due to limitations in cooling methods such as two-phase compositions and low melting point metal alloys, which require inert gases, are reactive, toxic, or costly, and have suboptimal thermal conductivity and diffusivity.
Innovation Solution
A piston with a sealed cooling gallery filled with a thermally conductive composition of bismuth and tin, which provides improved thermal properties, is used to dissipate heat from the upper crown, eliminating the need for inert atmospheres and simplifying metering and delivery, while withstanding high temperatures during manufacturing and operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a two-phase composition of silicone oil and copper particles is used in the cooling gallery, then heat redistribution is improved, but the system requires inert gas (argon) to prevent oxidative degradation and has metering/delivery manufacturing limitations
Solution Approach 1:
The patent changes the physical state and composition parameters by using a single-phase low melting point metal alloy (melting point 100-200°C) instead of a two-phase silicone oil and copper particles composition. This eliminates the need for inert gas protection and simplifies metering and delivery during manufacturing, while maintaining effective heat redistribution through the piston.
Solution Approach 2:
The patent replaces expensive and complex two-phase composition materials (silicone oil and copper particles requiring inert gas) with a simpler, cheaper single-phase low melting point metal alloy that does not require inert gas protection, reducing both material cost and manufacturing complexity.
2Temperature
If low melting point metal alloys including potassium, cadmium, sodium, lead, gallium, and indium are used in the cooling gallery, then thermal conductivity is improved, but the materials are reactive, toxic, or cost prohibitive
Solution Approach 1:
The patent replaces toxic and expensive low melting point metal alloys (potassium, cadmium, sodium, lead, gallium, indium) with a safer, cheaper alternative consisting of a low melting point metal alloy with melting point 100-200°C that is not reactive, non-toxic, and more cost-effective, while maintaining the required thermal conductivity for heat redistribution.
Solution Approach 2:
The patent converts the potential harm of using reactive and toxic low melting point metals into a benefit by selecting a specific alloy composition that eliminates reactivity and toxicity while preserving the low melting point property, thus transforming a harmful material selection into a safe and effective solution.
3Temperature
If high flow of cooling oil is maintained constantly to control piston temperature, then temperature control is improved, but the oil degrades over time due to high temperature and must be changed periodically
Solution Approach 1:
The patent changes the cooling medium from degradable cooling oil to a thermally conductive composition with melting point 100-200°C that does not degrade over time. This composition maintains effective heat transfer while eliminating the need for periodic oil changes, thus extending the service life of the cooling system.
Solution Approach 2:
The patent replaces the consumable cooling oil that requires periodic replacement with a non-consumable thermally conductive composition that remains stable and effective throughout the engine's operational life, eliminating maintenance costs and downtime associated with oil changes.
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 thermally conductive composition significantly enhances engine efficiency by effectively redistributing heat through the piston, reducing parasitic losses, and avoiding the use of reactive or costly materials, with improved thermal conductivity and diffusivity compared to previous solutions.
Implementation Method 1
the thermally conductive composition flows along the walls of the sealed cooling gallery and redistributes combustion heat from the upper crown through the piston body
Implementation Method 2
cooling oil is sprayed into the cooling gallery as the piston reciprocates along a cylinder bore of the engine. The oil flows along the inner surface of the upper crown and dissipates heat away from the upper crown
Data Source
AI summary
A heavy duty piston for an internal combustion engine comprises a thermally conductive composition filling 10 to 90 vol. % of a sealed cooling gallery. The thermally conductive composition includes bismuth and/or tin. For example, the thermally conductive composition can be a single-phase binary mixture of bismuth and tin. The thermally conductive composition has improved thermal properties, for example a melting point around 139° C., a thermal conductivity around 22 W/m·K, and a thermal diffusivity around 1.43E-5 m2/s. The thermally conductive composition is not reactive and does not include toxic or cost-prohibitive metals. During high temperature operation, as the piston reciprocates in the cylinder bore, the thermally conductive composition flows throughout the cooling gallery to dissipate heat away from the upper crown and thus improve efficiency of the engine.