Audi A3 Sportback g-tron is currently the only natural gas-powered model offered by Audi. The Audi A4 Avant g-tron will be the second one, arriving in late 2016, the company has announced.
The Avant g-tron will derive motive power from a new 2.0-liter TFSI turbocharged engine that is capable of 170 hp and 270 Nm of torque. Audi says that the pistons and valves of the new power plant are specially modified for gas operation and therefore provide an optimal compression ratio. An electronic controller is responsible for lowering the pressure of the gas stored in the tanks to working pressure, this means taking the pressure down from 200 bar to around 5 to 10 bars.
The tanks storing natural gas have to deal with very high pressures, hence Audi has made them using materials such as polyamide, Carbon Fiber-Reinforced Polymer (CFRP) and Glass Fibre-Reinforced Polymer (GFRP). Usage of these materials, claims the company, makes them lighter by 56 per cent as compared to steel cylinders and also makes them very strong; these tanks have been tested with pressure of up to 300 bar. Sheet steel shells with tensioning straps are employed to hold the cylinders in place and protect them against damage.
Four cylindrical CNG tanks are placed at the rear of the car in a compact module which also includes the 25-litre petrol tank. The gas tanks have a total holding capacity of 19 kg, giving the g-tron a driving range of 500 kilometers (310.7 miles) on gas alone. When the gas runs out, the petrol engine comes into play adding another 450 kilometers (279.6 miles); this gives the A4 Avant g-tron a total range of 950 kilometers (590.3 miles). In the European test cycle, the vehicle has consumed 4 kg of CNG (Compressed Natural Gas) per 100 kilometer with carbon emissions of 100 g/km (160.9 g/mile).
For safety reasons, the battery has been shifted to the engine compartment upfront and the filler necks for both gas and gasoline are under a common tank flap, enhancing convenience. The g-tron can also run on Audi e-gas which, the company says, makes it CO2 neutral in operation; e-gas is synthetic methane produced from water and CO2 with the help of green electricity in multiple power-to-gas plants.