Audi’s vision of future mobility primarily centers around an array of long-range electric cars scheduled to debut in the coming years under the "e-tron" badge.
These are intended to be Tesla killers, as they’re often called in Germany.
But there’s another kind of tron with a “made in Germany” label as well, and it’s not a robot from a 1990s science fiction movie: Audi’s g-tron cars run on compressed natural gas (CNG) as well as gasoline; running on natural gas emits less carbon dioxide per mile.
The second-generation A5 Sportback recently joined the A4 Avant wagon and the A3 in Audi’s CNG-powered family. It’s not coming to the United States, but we couldn’t resist the opportunity to take one for a quick spin in Germany.
Different kind of hybrid
The A5 g-tron has a turbocharged 2.0-liter 4-cylinder engine modified to run on CNG, with engine-management software from Bosch.
It's tuned to produce 170 horsepower between 4,450 and 6,000 rpm and 199 pound-feet of torque over a broad band from 1,650 to 4,400 rpm.
The turbo-4 is down on power compared to its gasoline counterpart, whose ratings check in at 190 hp and 236 lb-ft. An Audi spokesperson told us the compression ratio has been increased for part-load operation, which they predict will be the most common operating mode.
The TFSI engine powers the front wheels only; there’s no such thing as a g-tron quattro. A 6-speed manual transmission comes standard, but our test was fitted with the optional "S-tronic" 7-speed dual-clutch automatic transmission.
In this configuration, the A5 accelerates from 0 to 62 mph in 8.4 seconds and keeps going until 140 mph. It’s about a second slower to freeway speeds than the standard Sportback, yet it’s about half a second quicker than the base gasoline- and diesel-powered variants.
READ THIS: Truckers Slowly Warm To Cold Liquified Natural Gas (Sep 2015)
The CNG is stored in high-pressure tanks sandwiched under the passenger compartment. They’re made of such composite materials as carbon fiber and fiberglass to avoid adding too much weight to the car.
They store a total of nearly 42 pounds of gas at a pressure of 200 bars (2,900 psi), which provides the A5 with up to 500 miles of driving range on CNG alone. Switching to gasoline adds another 280 miles of range, according to Audi.
Theoretically, you could drive the g-tron from New York City to the outskirts of Chicago without needing to stop for fuel.
What’s in the tanks?
CNG is compressed methane stored under pressure. It’s relatively common in nations like Iran, Pakistan, Brazil, and Thailand. In Europe and North America, the CNG fueling infrastructure remains tiny.
When you do manage to find a station, refueling takes about as long as it would for a tank of gasoline. Natural gas is often cheaper than gasoline, too, not to mention lowering CO2 emissions.
CNG is not to be confused with liquid petroleum gas (LPG), a mixture of propane and butane that’s liquefied—hence its name—and stored under pressure. LPG can’t be considered a mainstream fuel either, though it has a small but loyal following in Europe.
CHECK OUT: Five Ways To Find Places To Refuel Your CNG, E85, Diesel Car (Feb 2012)
The g-tron is also capable of running on the "e-gas" fuel Audi manufactures in-house. It’s a synthetic natural gas produced in England and Germany since 2013. Using renewable wind energy, Audi splits water into oxygen, which is released back in the air, and hydrogen, which is retained.
The hydrogen reacts with CO2 extracted from the atmosphere to form methane, which is then routed into the European gas grid. Any CNG-powered machine, from our test A5 through the Napa Valley Wine Train to a stove on a sailboat, can run on Audi’s e-gas.
The g-tron looks exactly like a garden-variety A5, with the exception of a small emblem at the bottom right side of the trunk lid.
There’s no extra fuel door to show it’s capable of moving without burning gasoline, nor does it have slabs of shiny blue trim to announce it goes easy on the ozone layer. “Make it low-key” was the order to designers.