Description:The present invention relates to pressure vessels for the storage and transportation of compressed natural gas (CNG), and more particularly to a Type IV composite CNG cylinder that incorporates advanced multilayer liner technologies and filament-wound structural reinforcements, offering improved gas barrier performance, high-pressure durability, lightweight construction, and efficient manufacturing processes. The invention further includes a novel Preform-Assisted Shaping (PAS) method for improved dimensional stability and mechanical performance.
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Background of the Invention:
Type IV CNG cylinders have become increasingly important in applications such as alternative fuel vehicles, industrial gas transport, and storage systems due to their lightweight and corrosion-resistant construction. These cylinders typically consist of a plastic liner fully overwrapped with a fiber-resin composite.
Conventional liners, however, often face challenges such as:
• Poor gas barrier properties leading to gas permeation over time;
• Difficulty achieving uniform wall thickness and shape retention during blow molding;
• Delamination issues between polymer layers and composite overwrap;
• Insufficient impact and fatigue resistance in harsh environments.
Moreover, the manufacturing methods are often inefficient and fail to ensure repeatable structural performance under high-pressure cyclic loads. Therefore, there exists a need for a multilayer Type IV CNG cylinder with enhanced liner-barrier design and an optimized process for consistent, high-quality production.
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Summary of the Invention:
The invention titled T4 CNG Cylinder PAS-Initial introduces a multilayer liner system within a Type IV composite pressure vessel, combined with an optimized Preform-Assisted Shaping (PAS) and filament winding process to produce a lightweight, durable, and gas-impermeable cylinder for CNG applications.
Key innovations include:
• A co-injected multilayer liner comprising polyglycolic acid (PGA) for gas barrier, polyethylene terephthalate (PET) for strength and thermal stability, and optional tie-layers for adhesion;
• Precision blow molding to shape the liner with consistent wall thickness using a PAS technique;
• A structural overwrap using carbon fiber or hybrid fiber systems impregnated with epoxy or thermosetting resin;
• Integrated flanged neck or dome designs with metallic bosses for valve mounting;
• High resistance to cyclic fatigue, permeation, and impact loading, meeting global CNG standards (e.g., ISO 11439, NGV2, ECE R110).
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Brief Description of the Drawings:
• Figure 1: Cross-sectional view of the multilayer T4 CNG cylinder showing each material layer.
• Figure 2: Flowchart illustrating the PAS-Initial manufacturing process.
• Figure 3: Diagram of the blow molding setup with preform expansion stages.
• Figure 4: Filament winding pattern and composite overwrap details.
• Figure 5: End boss design and interface with the liner.
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Detailed Description of the Invention:
1. Liner Structure:
The inner liner of the T4 CNG Cylinder comprises:
• Inner Layer (Barrier Layer): Composed of polyglycolic acid (PGA), which has exceptional gas barrier properties, preventing methane and hydrogen leakage.
• Intermediate Layer: Made of PET or PEN, contributing mechanical strength and thermal resistance.
• Adhesive/Tie Layer: Optional functional polymer layer such as maleic anhydride grafted polyolefin, ensuring chemical bonding between the barrier and structural layers.
• Outer Layer (Interface Layer): Engineered for surface compatibility with the composite wrap (e.g., roughened PET or co-extruded polypropylene).
2. Blow Molding with PAS (Preform-Assisted Shaping):
The manufacturing process begins with co-injection molding of a multilayer preform. The PAS method uses:
• Controlled axial and radial preform stretching;
• Thermal conditioning at targeted temperatures for each layer;
• High-precision mold shaping to ensure uniformity and material alignment.
3. Composite Overwrap (Structural Layer):
• Fibers: Carbon fiber, aramid, or glass fiber in continuous tow form;
• Resin: Epoxy-based or thermoplastic resin system, cured post-wrapping;
• Wrapping Pattern: Helical and hoop windings with programmable angle variations;
• Optional: Hybrid wrappings using both carbon and glass fibers to balance cost and strength.
4. End Boss and Mounting:
• Metallic or composite inserted bosses are integrated into the dome or neck;
• Designed to receive valves, regulators, or burst disks;
• Interface sealed with O-rings or ultrasonic welding for high-pressure containment.
5. Performance Features:
• Working Pressure: 200–700 bar;
• Burst Pressure: > 3× working pressure;
• Cyclic Life: > 18,000 cycles per ISO 11439;
• Gas Permeation Rate: < 0.05 cc/l/day at 200 bar;
• Weight Reduction: > 40% over Type I or Type II cylinders;
• Compatibility: Hydrogen, Methane, Biogas, CNG blends.
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Advantages of the Invention:
1. Superior Gas Retention: Thanks to PGA’s ultra-low gas permeability.
2. Lightweight Design: Achieved via composite wrapping and liner material optimization.
3. Thermal and Impact Resistance: PET/PEN liners withstand elevated fill temperatures and road impacts.
4. Improved Manufacturability: PAS ensures uniform wall thickness and eliminates blow molding defects.
5. Cost-Efficiency: Hybrid fiber use and simplified liner molding reduce production costs.
, Claims:1. A multilayer Type IV CNG cylinder comprising:
o An inner barrier layer of polyglycolic acid (PGA);
o An intermediate thermoplastic structural layer;
o An adhesive layer disposed between the barrier and structural layers;
o A filament-wound overwrap comprising carbon or glass fiber;
o A metallic or composite boss inserted at the cylinder end.
2. The cylinder of claim 1, wherein the overwrap comprises both helical and hoop winding patterns impregnated with epoxy resin.
3. The cylinder of claim 1, manufactured by a process comprising:
o Co-injecting a multilayer preform;
o Stretch blow molding the preform into a liner via Preform-Assisted Shaping (PAS);
o Winding fiber-reinforced resin around the liner;
o Thermally curing the composite overwrap.
4. The method of claim 3, further comprising a post-cure annealing process to relieve internal stress.
5. A high-pressure gas storage system comprising at least one of the cylinders of claim 1, operable at pressures exceeding 300 bar.