Description:Field of the Invention:
The present invention pertains to the field of high-pressure storage systems, specifically Type IV Composite Overwrapped Pressure Vessels (COPVs). More particularly, the invention relates to an improved polymeric liner shape that allows maximum internal fluid capacity for a given external cylinder size while maintaining structural compatibility with fiber overwrap techniques and pressure requirements.

Background of the Invention:
Type IV cylinders consist of a non-metallic (typically polymeric) liner and a fiber-reinforced composite overwrap, widely used for storage of gaseous fuels under high pressure. The design of the internal liner significantly impacts the useable fluid capacity, mechanical integrity, and winding efficiency.
Traditionally, liner geometries have been based on standard dome and cylindrical designs, often without fully exploiting the volume potential. The main challenge has been optimizing the liner shape to maximize volume while staying within the constraints of manufacturing, filament winding, and pressure containment.
In existing art, the design focus has predominantly been on strength and material optimization, not volumetric efficiency. However, in real-world applications like vehicular hydrogen storage, capacity per unit volume and weight becomes critical.

Prior Art References:
1. US20070199690A1 – “Composite pressure vessel having optimized liner geometry” (mentions liner configuration for strength but not for maximizing internal volume).
2. EP2999573A1 – “Liner for pressure vessel” (focuses on improving gas barrier performance rather than maximizing volume).
3. US20140291341A1 – “Pressure vessel liner geometry for improved load sharing” (structural focus; capacity not optimized).
4. KR101954502B1 – “Design method of liner geometry in Type IV tank considering dome and knuckle radius” (capacity enhancement is secondary to structural distribution).
5. WO2019005231A1 – “High pressure gas storage tank with increased volume efficiency” (closely related, but geometry optimization is not described in detail or within specific size constraints).

Summary of the Invention:
The invention provides a liner shape that is meticulously designed to maximize the internal capacity of the pressure vessel without altering its external dimensions or compromising safety. The geometry includes:
• A wider cylindrical body within allowable diameter limits,
• A dome with reduced height and flatter curvature,
• Optimized transition zones between dome and cylinder,
• Provisions for boss mounting without intruding on storage volume.
This configuration enables a significant increase in the storage capacity of gases (like CNG or hydrogen), which directly impacts vehicle range, system efficiency, and manufacturing cost-effectiveness.
Drawings
Figure 1: Cross-section of the liner with dimensional annotations

Detailed Description of the Invention:
1. General Construction:
The pressure vessel comprises:
• A polymeric liner made from high-density polyethylene (HDPE), polyamide, or similar material.
• A composite overwrap of carbon fiber with epoxy resin.
• A metallic or non-metallic boss fitted at the dome ends for valve installation.
2. Liner Geometry:
The innovative shape involves the following features:
• Cylindrical Section Diameter (D):
o Maximized within the permissible outer dimensions of the vessel.
o Maintains compatibility with existing winding setups.
• Dome Shape:
o Reduced height (h): The dome is kept as shallow as possible to reduce unused headspace.
o Flatter curvature (radius of curvature ≥ 1.5D) compared to standard hemispherical or elliptical domes.
o Smooth transitional radius (r) from the cylindrical body to dome, which minimizes stress concentration while optimizing volume.
• Boss Insertion Region:
o Integrates a minimal protrusion into the dome region to retain usable gas volume.
o Boss neck length is reduced and conical taper minimized.
• End-to-End Length (L):
o Within regulatory and design limits, with reduced dome regions contributing to higher usable straight cylindrical volume.

The Fig. 1 illustrates, the liner is composed of a central cylindrical body flanked on either end by dome-shaped ends, with each dome integrating a neck region configured to receive a metallic or non-metallic boss for valve fitting. The design is characterized by dimensional optimizations that prioritize maximum internal volume while maintaining structural compatibility with composite overwrap processes and high-pressure operation.
The outer diameter (D) of the cylindrical section is maximized to the greatest extent allowed by the external pressure vessel envelope, typically ranging between 300 mm to 500 mm depending on the application. The overall length (L) of the liner, measured from end to end, ranges between 800 mm to 1600 mm. Within this total length, the straight cylindrical portion (Lc) is extended to occupy approximately 60% to 80% of the total liner length, ensuring that the main fluid-containing section is as large as structurally feasible. For example, in a liner with a total length of 1200 mm, the cylindrical portion would occupy approximately 900 mm.
Each dome-shaped end is designed with a reduced height (h), typically between 80 mm and 150 mm, and formed with a flatter radius of curvature (R), where R is generally equal to or greater than 1.5 times the diameter (1.5D). This shallower, flatter dome geometry minimizes the unutilized space commonly found in traditional hemispherical or elliptical dome designs, and allows for greater usable volume without compromising the stress distribution needed for pressure containment.
The transition radius (r) between the cylindrical body and the dome region is carefully controlled—usually between 50 mm and 75 mm—to ensure a smooth curve that avoids abrupt geometric changes, which can otherwise lead to stress concentration and failure during pressurization or overwrapping. The wall thickness (t) of the liner is generally maintained between 3 mm to 8 mm, depending on the selected polymeric material and pressure rating, such as HDPE or polyamide-based liners.
The neck region (N) at the apex of each dome is minimized to reduce its intrusion into the usable volume. Typically, this neck length ranges from 40 mm to 70 mm, just enough to securely seat the boss or valve mechanism without significantly consuming internal space. The dome opening angle (θ) is maintained between 70° to 110°, facilitating continuous fiber winding during the manufacturing process while preserving the desired internal geometry.
Through this design, the internal capacity (Vi) of the liner is increased by 10% to 12% compared to conventional dome geometries of the same external dimensions. This is achieved through a combination of extended cylindrical length, minimized dome height, flatter curvature, and shorter boss neck intrusions. The overall shape has been validated through CAD modeling and pressure simulation, confirming its suitability for use in high-pressure composite vessels designed to withstand burst pressures between 200 bar to 700 bar.
This geometry not only enhances the fuel-carrying capacity of the cylinder but also contributes to material efficiency, reduced overwrap requirements, and improved manufacturability using standard filament winding techniques.

Technical Advantages:
• Increased volumetric efficiency (up to 10–12% increase over conventional liners of the same size).
• Reduced material usage in overwrap due to better packing geometry.
• Enhanced range and performance for fuel cell vehicles.
• Compatible with existing Type IV cylinder production setups.
• Lower manufacturing cost per liter of gas stored.

Industrial Applications:
• Automotive industry (CNG or Hydrogen fuel tanks).
• Aerospace systems (compressed gas storage).
• Energy storage stations (stationary high-pressure tanks).
, Claims:1. A polymeric liner for a Type IV composite pressure cylinder, wherein the shape is configured to maximize internal volumetric capacity for a fixed outer dimension.
2. The liner of claim 1, comprising:
o A cylindrical section of maximized diameter (D),
o Dome-shaped ends of minimized height (h) and shallow curvature (radius ≥ 1.5D),
o Transition radius (r) designed to minimize volume loss and stress concentration.
3. The liner of claim 1, wherein the total dome height at both ends is reduced to increase cylindrical storage length.
4. The liner of claim 1, wherein the dome curvature follows a near-spherical segment with flatter midsections.
5. The liner of claim 1, wherein the boss connection area is recessed and does not significantly intrude into the storage volume.
6. The liner of claim 1, wherein the dome region features a blend radius with the cylindrical body to avoid abrupt transitions.
7. The liner of claim 1, wherein the shape increases gas capacity by at least 10% over conventional elliptical or hemispherical liners of the same overall length.
8. The liner of claim 1, wherein the liner is suitable for filament winding of carbon or glass fiber composite layers without inducing fiber slippage.
9. The liner of claim 1, wherein the polymeric material is selected from high-density polyethylene (HDPE), polyamide, or a multilayer composite structure.
10. The liner of claim 1, wherein the design is optimized via computational modeling to balance stress distribution and capacity.