Testing Composite CNG Vehicle Fuel Cylinders

Southwest Research Institute is evaluating the long-term performance of composite cylinders, such as the types shown in a major program involving cylinder manufacturers.

With the increasing use of compressed natural gas (CNG) as a vehicle fuel, suppliers and manufacturers are challenged to ensure the durability and safety of CNG cylinders.

Southwest Research Institute (SwRI) is a leader in research and testing of CNG cylinders, providing special techniques to valuate the long-term performance of these cylinders in a range of operating environments. Institute engineers are currently performing a battery of two-year, full-scale tests on composite cylinders under simulated service conditions consisting of a combination of pressure cycling, impact damage, and environmental exposure. These tests assess the long-term durability of composite cylinders under simulated service conditions. This program is being funded by the Gas Technology Institute, the Department of Energy and the Department of Transportation; it includes major composite cylinder manufacturers.

Specific SwRI capabilities include:

• Full-scale burst testing
  
• Full-scale sustained load testing
  
• Full-scale pressure cyclic testing Impact testing and modeling, including pendulum impact to 4,000-lb masses
  
• Environmental testing including high- and low-temperature testing and exposure to corrosive environments
  
• Permeability testing on plastic-lined cylinders utilizing advanced gas chromatography and mass spectrometry
  
• Detailed computational mechanics analyses

In addition to these test and analysis capabilities, SwRI has developed a unique acoustic emission (AE) system to evaluate the condition of composite cylinders. This system uses a source location technique that is capable of distinguishing between real damage and background noise--a major problem in conventional AE testing. The system precisely locates impact damage in the cylinders that may not be detected during visual inspection and will be used to monitor the evolutionof damage in the cylinders over long-term testing.

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