Study to methodize the design of a safe Type-4 CNG storage vessel using finite element analysis with experimental validation
Graphical abstract
Introduction
Natural gas is a cost-effective [1], environment-friendly [2], and abundant source of conventional energy [3,4], acting as an asset to humankind because of its sufficient availability and safe operability [5]. It considerably emits less toxic emissions [6], making its usage an excellent solution for surmounting the current pollution problems. The usage of natural gas in the transportation sector was restricted due to its low energy density. The energy generated by 1000L of natural gas is equivalent to that produced by 1L of gasoline or 1.1L of diesel [7]. Availability of limited storage space restricts fuelling the statutory amount of fuel, providing a small driving range. Therefore, it is either used as Compressed Natural Gas(CNG) stored at 20 MPa pressure at ambient temperature or as Liquefied Natural Gas (LNG) at an ultra-low temperature of −162 °C at atmospheric pressure [8]. This study focuses on the development of light-weight Type-4 composite pressure vessels for the storage of CNG. CNG stored at a pressure of 20–25 MPa can give the desired driving range in the available cargo space. The reduced weight of composite vessels over metallic cylinders can act as the most significant support, improving fuel efficiency in the case of automotive applications [9]. However, storing the gas at high pressure has resulted in various accidents, relating to the burst or leakage of CNG cylinders [10]. The cylinders are utilized for onboard CNG storage only after they pass the safety standards of ISO 11439 but the operating cylinders sometimes fail, causing heavy casualties due to the statistical probability of afflicting defects during manufacturing. The design model is developed in the ANSYS workbench, which focuses on reducing the probability of inflicting defects in the cylinder while winding the composite overwrap. A type-4 pressure vessel is manufactured at a state-of-the-art facility that possesses the necessary expertise related to composite manufacturing technology. The composite is the load-bearing component of a type-4 cylinder, which is wound using optimized machine parameters to yield a high-performing, low-cost product with little to no manufacturing defects. The manufactured prototype is further tested for leakage and burst as per ISO 11439 for validating the design model.
Section snippets
Materials and methods
A type 4 composite pressure vessel is designed to account for the least value of vessel weight to increase the fuel economy. The storage of CNG is a risky task that can be accomplished following the norms of ISO 11439 [10]. The cost of the system should be minimum without compromising its safety. A 4-axis filament winding machine is used for manufacturing high-performing type-4 cylinders; polymer liners with carbon-epoxy overwrap constitute the type-4 cylinder. To reach commercial deployments,
Theory and calculations
The designing of a pressure vessel involves a variety of parameters based on its working pressure, burst pressure, and material properties. The details of the pressure vessel design are determined based on the system properties given in Table 1.
FEA results
The designed pressure vessel is analyzed to compute its burst pressure based on maximum principal stress failure theory. The stress corresponding to failure gives the value of burst pressure. The obtained pressure vessel should withstand the necessary burst pressure of 470 bar per ISO 11439. For a carbon-epoxy composite after considering hygrothermal effects, the design yield strength is calculated to be 1839.36 MPa. The value of input pressure, which is simulated to generate principal stress
Conclusion
The entire methodology to design and manufacture a type-4 CNG storage pressure vessel was presented along with experimental validation. The analytical method for simulating the burst pressure was developed, incorporating various reformations in the existing methodology to ensure the least chances of inflicting manufacturing defects in form of fiber slippage or breakage during winding. The developed methodology can be used to manufacture lighter pressure vessels for different driving ranges by
Authorship statement
Conception and design of study: S. Neogi, P. Chugh, P. Sharma; acquisition of data: P. Sharma, S. Neogi; analysis and/or interpretation of data: P. Sharma, S. Neogi. Drafting the manuscript: P. Sharma, S. Neogi, P. Chugh. Revising the manuscript critically for important intellectual content: P. Sharma, S. Neogi, P. Chugh. Approval of the version of the manuscript to be published (the names of all authors must be listed): P. Sharma, S. Neogi, P. Chugh.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
This research is supported by a research program of “Development of Light-weight Composite Cylinders for Storage of Compressed Natural Gas (CNG)” of GAIL (India) Limited, New Delhi, India.
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