General Motors has subjected the compressed natural gas (CNG) fuel tank of its 2015 Bi-fuel Chevrolet Impala to several extreme tests, including the "bonfire test," penetration test with an armor-piercing rifle round, and impact testing.
The vehicle's CNG tank is covered by a large piece of cast aluminum that also protects connection points from certain side impacts. Sheet metal plates on either side of the tank help protect it from loose objects in the trunk or rear seat, according to GM.
“We designed this system for those ‘what if’ situations,” said Nichole Kraatz, Impala chief engineer.
The bonfire test subjects the tank to a steady 800-degree Fahrenheit fire to confirm that the CNG tank's pressure relief valves remain operation and the tank won't rupture. The tests are done at two fuel levels.
The penetration test involves engineers filling the tank to its service pressure. The tank is then shot with a 7.62 mm rifle round. The 7.62x51 mm NATO round travels at a velocity of more than 2,500 feet per second.
Additionally, the automaker conducted front barrier, side impact, and rear impact crash tests. The tank also undergoes long-term structural integrity tests equivalent to 15,000 pressure cycles and hydrostatic bursting tests of up to 8,100 PSI, according to GM.
The steel trunk-mounted CNG tank holds approximately 7.8 gallons, which is sufficient for about 150 miles of driving. The Impala then switches to gasoline power.