I. Basic Composition and Technical Standards

1. Formulation and Components

• The fluid is formulated with phosphate ester compounds as the base oil (primarily triaryl phosphates), supplemented with antioxidants, corrosion inhibitors, viscosity index improvers, and other additives. Its chemical composition complies with national environmental and toxicity regulations.

2. Compliance Standards

• Conforms to SAE AS1241D standards and meets the Civil Aviation Administration of China (CAAC) technical specifications for aviation fire-resistant phosphate ester hydraulic fluids (CTSO-2C706), covering physical-chemical properties, application performance, and bench testing. Based on its viscosity, auto-ignition point, and other parameters, the 4356 fluid is classified as either a Type IV or Type V hydraulic fluid.

II. Core Performance Characteristics

1. Fire Resistance

• Auto-ignition point exceeds 550°C, ensuring no sustained combustion upon exposure to flames, significantly reducing fire risks in high-temperature or open-flame environments. This aligns with the extreme safety requirements of aviation hydraulic systems.

2. Viscosity-Temperature Behavior and Fluidity

• Stable kinematic viscosity across a wide temperature range (-53.9°C to 126.7°C). Excellent low-temperature fluidity (operational at -40°C) with a pour point as low as -60°C, making it suitable for broad temperature-range operations.

3. Material Compatibility

• Compatible with metals, seals, and hoses. However, incompatible materials such as ethylene-propylene rubber (EPR) and butyl rubber must be avoided.

4. Environmental and Toxicity Considerations

• Emphasizes low toxicity compared to traditional phosphate ester fluids but still requires strict adherence to safety protocols. Hydrolysis over prolonged use may generate acidic byproducts, necessitating purification systems (e.g., activated clay filtration) to maintain performance.

III. Applications and Aircraft Compatibility

1. Primary Use Cases

• Designed for hydraulic systems in large civil aircraft, including COMAC ARJ21-700, C919, and other domestic and international aircraft models.

2. Component Compatibility

• Suitable for critical hydraulic components such as sleeve-bearing gearboxes, axial piston pumps, and centrifugal pumps, meeting high-pressure (<40 MPa) and high-temperature (-55°C to 150°C) operational demands.

IV. Technical Specifications and Quality Control

1. Testing Parameters

• Physical-chemical properties: Appearance, kinematic viscosity (multi-temperature testing), acid number, density, flash point (171°C), fire point (182°C), auto-ignition point, etc.

• Contaminant analysis: Strict control of chlorine, calcium, sulfur, and other chemical contaminants.

• Bench testing: Simulates real-world conditions to validate lubricity, anti-wear performance, and system compatibility.

2. Packaging and Storage

• Packaged in 3.5 kg/sealed containers, requiring storage in dark, dry, and ventilated conditions. Avoid exposure to impact or direct sunlight.

V. Market Positioning and Competitors

1. Comparison with Competing Products

• Compared to international brands like Skydrol LD-4 and Exxon HyJet V, the 4356 fluid offers advantages in localization compatibility, cost-effectiveness, and alignment with domestic standards.

2. Limitations

• Higher cost than mineral oil-based hydraulic fluids and stringent storage/operational requirements limit its adoption in non-aviation sectors.

VI. Summary and Outlook

The 4356 phosphate ester fire-resistant aviation hydraulic fluid has become a critical material for domestic aircraft hydraulic systems due to its exceptional fire resistance, wide-temperature adaptability, and compatibility with civil aviation platforms. Future development should focus on improving hydrolytic stability, reducing lifecycle costs, and advancing eco-friendly additive technologies to meet stricter aviation sustainability requirements.