GM says that it has tested the compressed natural gas (CNG) tank in the 2015 Bi-fuel Chevrolet Impala (earlier post) under normal and extreme conditions, exceeding both federal requirements and CNG industry guidelines. For example:
|The Bi-fuel Impala is subjected to six crash tests at GM’s Milford Proving Ground. Click to enlarge.|
The industry-standard Bonfire Test confirms the CNG tank’s pressure relief valves are operational and help prevent the tank from rupturing in a fire. In addition to placing the tank about four inches above a steady 800 ˚F fire, General Motors’ engineers added trunk, back seat and underbody fires to test the pressure relief valves’ ability to sense heat on all sides of the tank. The tests were done at two different fuel levels.
In the Penetration Test, the tank is filled to its service pressure and is shot with a 7.62 mm armor-piercing bullet. In order to pass the test, the bullet has to pass completely through one side of the tank without exiting out the other side. The goal is to have the tank maintain the bullet hole only as the weak structural point, without rupturing.
Front barrier, side impact and rear impact crash tests were conducted on the Bi-Fuel Impala. Some aftermarket CNG-conversion kit manufacturers conduct only a barrier test. 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. The tank's normal operating pressure is 3,600 PSI.
The tanks also undergo hydrostatic burst testing, in which tanks are filled with water until they bursts; tanks must hold up to at least 8,100 PSI.
A large piece of cast aluminum helps protect the tank valve and connection 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.
The all-steel trunk-mounted CNG tank holds approximately 7.8 gallons, sufficient for about 150 miles of driving after which the Impala seamlessly switches to gasoline power. The complete CNG system is covered by Chevrolet’s five-year, 100,000-mile—whichever comes first—limited powertrain warranty and can be serviced at Chevrolet dealerships throughout the US and Canada.
We designed this system for those ‘what if’ situations. 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.—Nichole Kraatz, Impala chief engineer
The Bi-fuel Impala—a 2015 “Green Car of the Year” finalist—is the auto-industry’s only manufacturer-produced full-size sedan in North America that runs on both CNG and gasoline. It is available to order now through all Chevrolet dealerships in the US and Canada with delivery expected at the end of this year.