Plenty of high-end sports cars feature glass panels into the engine bay, letting you glimpse the works of mechanical art beneath. Glass engines though are altogether rarer, for obvious reasons. But that does present a problem when you want to inspect the combustion process a little closer in laboratory testing--how do you see whether the real engine is working the way the computer model predicts? If you're Audi, you put a small window of quartz glass in the walls of the combustion chamber to study your eco-friendly 'e-fuels'.

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Audi has made significant strides in recent years with cleaner vehicles and cleaner fuels to power them. One of these is 'e-gas', a synthetic natural gas designed for use in the Audi A3 g-tron hatchback launched in Europe last year. Externally identical to other current-generation A3 hatchbacks, and largely similar under the hood too, the g-tron runs on a specially-designed composition of natural gas. Chemically, it's identical to regular natural gas so runs exactly the same in an appropriately-built engine. But the synthetic nature means the e-gas is as "pure" as fuel gets--there are no unwanted hydrocarbons in the fuel, so it burns more efficiently and burns cleaner than regular natural gas fuels.

You can measure cleanliness from the tailpipe, but Audi's engineers wanted to see the combustion process for themselves. A small glass window in a specially-designed engine, running up to 3,000 rpm, provides an insight into how the combusting fuel behaves. A further test uses a compression chamber and a special camera to observe the injection process. The challenge now is to take that knowledge and use it to optimize the production process for e-ethanol and e-diesel, too--providing cleaner fuels for all internal combustion vehicles.

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Production of the e-gas itself is already well underway at the firm's plant in Werlte, Germany. It's set to produce around 1,000 metric tons of e-gas per year--during which the only by-products are water and oxygen. It'll be enough to power 1,500 Audi A3 Sportback g-tron models for around 9,300 miles each, every year.


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