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Audi e-gas – new fuel

The Company is establishing a portfolio of sustainable sources of energy as part of its Audi e-gas project. Renewably generated electricity from wind or solar power, water and carbon dioxide are used to produce hydrogen and synthetic methane, the Audi e-gas. The plant that Audi has built in Werite near Emsland is now in the commissioning phase. It produces the fuel for the first CNG model from Audi, the new A3 Sportback g-tron, which will be launched before the end of the year.


How the Audi e-gas facility works

The e-gas plant’s work comprises two major process steps: electrolysis and methanation. In the first step, the plant’s three electrolyzers use renewably generated electricity to split water into hydrogen and oxygen. The hydrogen could one day power fuel-cell vehicles. The infrastructure for this is not yet in place, however, which brings us to the second process step. The hydrogen is then reacted with CO2 to produce synthetic methane, or Audi e-gas. It is virtually identical to fossil natural gas and thus can be distributed via the German natural gas network to CNG filling stations for sale.

The carbon dioxide used by the Audi e-gas plant comes from the exhaust flow of an adjacent biomethane plant operated by the energy utility EWE. The carbon dioxide is separated from the biogas produced from organic waste to obtain high-purity biomethane. The Audi e-gas plant is expected to produce roughly 1,000 metric tons of e-gas per year, thus binding approximately 2,800 metric tons of CO2 that would otherwise pollute the atmosphere.

The efficient use of energy flows is a top priority throughout the entire production sequence of the e-gas plant, which Audi built in collaboration with the plant construction specialist ETOGAS. The waste heat produced during methanation is used to hygienize the wastes and treat the biogas, greatly increasing overall efficiency. The Audi e-gas plant is scheduled to begin feeding the synthetic gas into the network in summer 2013.


An avenue for the energy industry

The Audi e-gas project transcends the automobile industry. It shows how large amounts of wind or solar energy can be stored efficiently and independently of location by transforming it into methane gas and storing it in the natural gas network, the largest public energy storage system in Germany. With the e-gas project, Audi is both a part of and a driver of the energy revolution. Major German energy utilities have since taken up the idea of power-to-gas cogeneration and are following Audi with initial projects of their own.

Just like fossil natural gas, Audi e-gas is ideally suited as a fuel for combustion engines. It is anticipated that the CO2-neutral e-gas from Werlte will power 1,500 new Audi A3 Sportback g-tron vehicles 15,000 kilometers (9,320.57 miles) every year. A balancing system will ensure that the amount of e-gas fed into the system is equivalent to the amount of gas customers pump at CNG filling stations.


Extremely low fuel costs

The new Audi A3 Sportback g-tron consumes on average less than 3.5 kg of e-gas per 100 km. Customer fuel costs are in the vicinity of 4 euros per 100 km; tailpipe CO2 emissions in the NEDC cycle are less than 95 grams per km (152.89 g/mile). Driving with Audi e-gas is climate-neutral – the CO2 generated when the vehicle is driven has been bound previously during production of the e-gas. Even in a comprehensive wheel-to-well analysis that includes the construction and operation of the e-gas plant, CO2 equivalents remain below 20 grams per km (32.18 g/mile).

The Audi A3 Sportback g-tron features state-of-the-art CNG technology (CNG = compressed natural gas), beginning with the pressurized storage of the fuel. The two cylinders under the luggage compartment floor that store the natural gas or e-gas at a pressure of roughly 200 bar (2,900 psi) have a capacity of 7 kg (15.43 lb) each. They largely occupy the space normally taken by the spare wheel well.

Designed according to the Audi lightweight construction principle, the cylinders weigh 70 percent less than conventional steel cylinders, with each representing a weight saving of 27 kg (59.52 lb). They feature an innovative structure. A matrix of gas-impermeable polyamide comprises the inner layer, while a second layer of carbon fiber-reinforced polymer (CFRP) gives the tank its extremely high strength; a third layer of glass fiber-reinforced polymer (GFRP) provides protection against damage from the outside.


Electronic gas pressure regulator

A second highlight of the Audi A3 Sportback g-tron is its electronic gas pressure regulator. This compact and lightweight component reduces the high pressure of the e-gas flowing from the cylinders down to around five to nine bar (72.5 to 130.5 psi) in two stages. It ensures that the right 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 when the driver wants more power and torque.

With roughly 0.6 kg (1.32 lb) of gas remaining, the pressure in the tank drops below 10 bar (145 psi) and the engine management system automatically switches over to gasoline mode. The Audi A3 Sportback g-tron is fully bivalent. It has an NEDC range of 400 km (248.55 miles) with natural gas or e-gas and another 900 km (559.23 miles) with gasoline. Current fuel consumption can be seen at all times in the driver information system. Two displays in the instrument cluster indicate the fill level of the tanks, whose filler necks are located under a common fuel door.

After refueling, and whenever it is very cold, the Audi A3 Sportback g-tron is started with gasoline initially, then it is switched over to natural gas as quickly as possible. Its engine is a modified 1.4 TFSI. The cylinder head, turbocharger, fuel injection system and catalytic converter have been designed specifically for operation with e-gas. Developing 81 kW (110 hp) and 200 Nm (147.51 lb-ft) of torque, the five-door car accelerates from 0 to 100 km/h (62.14 mph) in 11.0 seconds. Its top speed is over 190 km/h (118.06 mph).