GM details bullet, bonfire tests for bi-fuel Chevy Impala

The penetration, fire and impact tests are designed to ensure that natural gas safely vents, rather than rupturing the tank.

General Motors has outlined the rigorous safety tests that are designed to verify the safety of compressed natural-gas cylinders used in the bi-fuel Chevrolet Impala.

The company claims to have gone above and beyond industry standards and federally-mandated test requirements, ensuring tank integrity even in extreme situations.

The CNG cylinder has been placed a few inches above an 800-degree fire to test the pressure-release valves. Engineers also added fires in the trunk and back seat for additional verification, with tests completed at two different fuel levels.

The penetration trial requires the tank to be filled to its service pressure of 3,600 PSI and shot with a 7.62mm armor-piercing bullet. The tank is not designed to deflect a bullet from an AK-47, but the projectile must only pass through one side of the tank without exiting the other side or causing the cylinder to completely rupture.

A series of front-, rear- and side-impact crash tests put to test GM's overall vehicle design and sheet-metal barrier plates located around the tank. The company also fills the tank 15,000 times to ensure long-term structural integrity, while hydrostatic bursting pressure must exceed 8,100 PSI.

"We designed this system for those ‘what if' situations," said Impala chief engineer Nichole Kraatz. "The customer shouldn't even know it's there. They shouldn't even think about it. CNG should just be another fuel they use to power their vehicle."

The CNG tank takes up some trunk space, but it provides an extra 150 miles of driving range before the car automatically switches to gasoline power.

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