Audi makes fuel cells look good with the A7 Sportback h-tron

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The Audi A7 Sportback h-tron quattro

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One of the biggest tech stories at this year's LA Auto Show was the fuel cell car. Toyota led the way by launching the Mirai, and Volkswagen slid a fuel cell powertrain into the Golf SportWagen. Audi showed a sportier, more luxurious side to fuel cells in the A7 Sportback h-tron quattro. Ingolstadt calls it the "first performance fuel cell vehicle."

Despite its interesting AWD, fuel-cell-based plug-in hybrid powertrain, the A7 Sportback h-tron was a bit of a sideshow for Audi, pushed to a quieter part of its LA stand to make room for the true centerpiece: the Prologue concept. While not quite as flashy, the h-tron design offered an equally telling look at the future of the four rings.

Building on an e-quattro configuration of front- and rear-mounted motors, Audi slid a 300-cell stack power unit into the drive system. When topped off with hydrogen, the fuel cell stack offers up to 310 miles (500 km) of range.

"The core of each of these individual cells is a polymer membrane," Audi says in describing the fuel cell operation in more detail. "There is a platinum-based catalyst on both sides of the membrane. Hydrogen is supplied to the anode, where it is broken down into protons and electrons. The protons migrate through the membrane to the cathode, where they react with the oxygen present in air to form water vapor. Meanwhile, outside the stack the electrons supply the electrical power."

A below-trunk, 8.8-kWh lithium-ion battery adopted from the A3 Sportback e-tron serves as a backup, providing an extra 31 miles (50 km). The driver can rely on battery power alone by selecting EV mode. The battery charges via brake recuperation and can also be plugged in and charged in four hours from a 230-volt outlet or two hours from a 360-volt source.

The h-tron concept car looks like a standard A7 on the outside but has some key changes on the other side of the doors and hood. The fuel cell stack takes the engine's place under the hood and works in conjunction with a turbocharger (forces air into the cells), recirculation fan (returns unused hydrogen to the anode to increase efficiency) and a dedicated coolant pump. The instrument panel has been updated with battery and hydrogen fuel level indicators, as well as a power flow meter in place of the engine rev counter.

Audi took advantage of the water vapor-only emissions of fuel cell technology, saving weight with a plastic exhaust system. The h-tron flicks the scale's needle to 4,299 lb (1,950 kg).

Not unexpectedly, the 228-hp (170-kW), 398 lb-ft (540 Nm) fuel cell powertrain has a sharp performance drop when compared to the 310-hp (231-kW) 3.0-liter TFSI 2015 A7. The A7 h-tron does the 0-62 mph (100 km/h) sprint in 7.9 seconds, compared to the ~5.6-second time of the TFSI version. The h-tron tops out just under 112 mph (180 km/h), compared to the 130-mph (209-km/h) electronic limit of the ICE production model.

The h-tron makes up for its slowed performance by puffing out nothing but water vapor and bringing home an estimated fuel economy of 62 miles (100 km) per 2.2 lb (1 kg) of hydrogen. A kilogram of hydrogen has roughly the same energy content as a gallon of gas, so that equates to 62 mpg when compared to gas vehicles. The quartet of tanks holds 11 lb (5 kg) of hydrogen, and Audi says the system takes about three minutes to fill.

Fuel cell vehicles like the Hyundai Tucson Fuel Cell and Honda FCX Clarity have already launched in Southern California, an area of the US with enough of a hydrogen fueling infrastructure to make hydrogen-fueled cars viable, and the Toyota Mirai will soon join them in the Golden State. Audi appears to be taking a more cautious path, remaining noncommittal as to the h-tron's potential launch timeframe.

"The h‑tron concept car shows that we have also mastered fuel cell technology," says Prof. Dr. Ulrich Hackenberg, member of Audi's Board of Management for Technical Development. "We are in a position to launch the production process as soon as the market and infrastructure are ready."

The h-trons in LA were fully working technology demonstrators, and Audi even offered test drives. It also pointed out that the show car was essentially what the production model would look like.

Source: Audi

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