Power From Gas: The New Audi A4 Avant G-Tron

Sporty, versatile and completely CO2-neutral, if desired: Scheduled to launch in late 2016, the A4 Avant g-tron* is yet another offer from Audi for the sustainable mobility of the future. It follows the A3 Sportback g-tron* as the brand’s second model to use natural gas or climate-friendly Audi e-gas.

The new Audi A4 Avant g-tron

The A4 Avant g-tron is simultaneously sporty, efficient and extremely economical. The engine is based on the new 2.0 TFSI featuring an advanced, highly efficient combustion process developed by Audi. The turbocharged power plant produces 125 kW (170 hp). Maximum torque of 270 Nm (199.1 lb-ft) is available at approx. 1,650 rpm. The pistons and valves have been specially modified for gas operation and allow for an optimal compression ratio. An electronic controller reduces the high pressure of the gas flowing from the tank from as much as 200 bar to a working pressure of 5 to 10 bar in the engine. This pressure control function is performed dynamically and precisely in response to the power requested by the driver. The correct pressure is always present in the gas line and at the injector valves – low pressure for efficient driving in the lower speed range, and higher pressure for more power and torque.

In the NEDC, the Audi A4 Avant g-tron consumes less than four kilograms CNG (compressed natural gas) per 100 kilometers (8.8 lb), corresponding to customer fuel costs of roughly four euros (as of: October 2015). CO2 emissions are less than 100 grams per km (160.9 g/mile). The tank capacity of 19 kilograms (41.9 lb) of gas allows for a range of over 500 kilometers (310.7 mi). When the amount of gas remaining drops below approx. 0.6 kilograms (1.3 lb) – analogous to a residual pressure of 10 bar – the control unit switches to gasoline operation. The bi-fuel A4 Avant g-tron can cover an additional 450 kilometers (279.6 mi) in this mode. The potential overall range is comparable to that of a car with a TDI engine.

The filler necks for gas and gasoline are located under a common tank flap. After refueling, and whenever it is very cold, the engine is started with gasoline initially, then switched over to natural gas operation as quickly as possible. Two displays in the instrument cluster keep the driver up-to-date on the fill levels of the tanks. The driver information system shows the fuel consumption in the active operating mode.

Audi installs the four cylindrical CNG tanks as a compact module in the rear end of the Avant. They are optimized for the available space, and each is specifically sized. Sheet steel shells with tensioning straps hold the cylinders and protect them against damage, such as curbs. The complete CNG tank module, which also includes the 25 liter (6.6 US gal) gasoline tank, is fitted to the body during production of the A4 Avant. The spare wheel well in the body is eliminated. The battery also moves from the luggage compartment to the engine compartment. The loading floor is even with the loading lip, thus offering a full-fledged luggage compartment.

The CNG tanks with an operating pressure of 200 bar at 15 degrees Celsius follow the Audi lightweight construction philosophy. Thanks to their innovative layout, they weigh 56 percent less than comparable steel cylinders. Their inner layer is a gas-tight matrix of polyamide. The second layer, a composite winding of carbon fiber-reinforced polymer (CFRP) and glass fiber-reinforced polymer (GFRP), provides for maximum strength. The third layer is pure GFRP and serves primarily as a visual inspection aid, turning milky white where damaged. Before being installed in a car, each tank is tested at 300 bar during production. The actual bursting pressure is much higher still and far exceeds the legal requirements.

With Audi e-gas, the A4 Avant g-tron is CO2-neutral in operation. e-gas is a synthetic methane produced from water and CO2 with the help of green electricity in multiple power-to-gas plants. Audi operates the world’s first industrial-scale power-to-gas plant in Werlte, but now also procures e-gas from other facilities. With power-to-gas technology, the brand with the four rings is making it possible to store excess renewable energy – a valuable contribution to the energy transition. The company and its partners are intensively driving the development of various synthetic fuels known as Audi e-fuels, including by means of new biological production processes.

The driver can buy fuel using the Audi e-gas refueling card familiar from the Audi A3 Sportback g-tron, which serves as both a payment and balancing instrument. Based on the information transferred during payment, Audi feeds e-gas corresponding to the amount of gas purchased by the customer back into the natural gas network. In this way Audi achieves completely CO2-neutral mobility.

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