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Audi A5 Sportback g-tron - game of trons
In terms of technology under the skin, the A5 Sportback g-tron is practically a clone of its A4 Avant g-tron sibling. To the point where even fuel consumption and driving range on a single refill are the same. So just to remind you: under the bonnet there's a 2-litre TFSI engine good for 170 PS of power and 270 Nm of torque. Paired to the S Tronic gearbox and fueled with methane, it emits just 100 grams of CO2 per kilometre, which means it only consumes below 4 kg/5,34 m3 of CNG per 100 km. With 19 kg/25,38 m3 of gas compressed to 200 bar on board, the car is supposed to cover nearly 500 km on a single top up. Once pressure in the tanks drops below 10 bar (which is equivalent to there being some 0,6 kg of fuel left), the engine seamlessly switches over to petrol and can drive another 450 km before the other fuel runs out. Clean and green as it is, the car doesn't compromise performance, though – the 2-litre unit propels it from standstill to 100 km/h in a respectable 8,5 s.
As for the rear-mounted CNG tanks, they're ultralight and extremely durable at the same time. They make do without steel or aluminium altogether, replacing them with polyamide wrapped in carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP) and bound together with epoxy resin. The engine has been modified to better meet specifics of methane as its primary fuel – it features a shortened compression stroke, a long power stroke and increased compression ratio to improve part load operation efficiency. The intake valves close sooner than usual, which – combined with increased pressure in the intake manifold – reduces throttle losses.
The most interesting part, though, is the methane fuel itself, which Audi produces on its own. This doesn't mean owners of the A5 Sportback g-tron will have special refueling stations just to themselves – it's more like offsetting the environmental impact of regular, fossil-sourced natural gas. To date, Audi has been making their so called e-gas from CO2 and hydrogen using wind-generated electricity, but the method has been improved and is about to change. The new technology involves biomethanation by microorganisms. The new process is said to be more efficient and is carried out at lower pressure and temperature.
Buyers of Audi's methane-powered range (also including the A3 Sportback g-tron) receive special refill cards, which provide the manufacturer with information regarding amounts of fuel they buy and use. To offset the actual tailpipe emissions of their cars, Audi supplies the methane grid with their carbon-negative e-gas, thus making g-trons virtually carbon-neutral on a well-to-wheel basis. Let's hope other brands of the Volkswagen Group will also soon benefit from this innovative solution, especially since Volkswagen, Skoda and Seat already have CNG-powered models in their line-ups.
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