Putting a compressed natural gas tank in the trunk of a car is potentially hazardous, which is why all CNG tanks slated for use in automotive applications must undergo a rigorous series of tests. Chevrolet says its 2015 Bi-Fuel Impala, which can travel an additional 150 miles thanks to a 7.8 gallon CNG tank, exceeded requirements when undergoing these federal tests.
The tank in the Impala CNG is mounted in the trunk, and has a normal operating pressure of about 3,600 PSI. To protect it from puncturing, Chevrolet put sheet metal plates on either side of the tank and laid cast aluminum over the tank valve connection. This helps prevent loose objects in the trunk damaging the valve or the tank itself.
An industry-standard Bonfire Test helps ensure the CNG tank’s pressure relief valves operate correctly and can help prevent it from rupturing in the event of a fire. The tank is placed about four inches about an 800-degree Fahrenheit fire, where the valves will sense heat and open, releasing the CNG gases.
The CNG tank is also safe from explosions after being shot. The Penetration Test entails shooting the tank with a 7.62mm armor-piercing round, which should pass through only one side of the tank and not the other, assuming the tank works as designed. A front barrier, side and rear impact crash test ensure the tank won’t rupture or explode in the event of a collision.
“We designed this system for those ‘what if’ situations,” said chief Impala 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 Bi-fuel Impala is currently the only manufacturer-produced full-size sedan that runs on both gasoline and CNG. Chevrolet dealerships area already taking orders, with deliveries set to commence before the end of the year.