GTL flight is key part of process to make synthetic fuel available

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Today's gas-to-liquid kerosene demonstration flight operated by Qatar Airways marks a key part of the test and demonstration process which should see the synthetic fuel available for regular airline services within three years.

A Qatar Airways Airbus A340-600 operated the world's first revenue flight fuelled by a 50/50 mix of GTL kerosene and oil based Jet A1 on 12 October. As well as providing a new source of fuel supply, the alternative fuel is expected to provide local air quality benefits at airports due to its cleaner burning characteristics, says Gary Woodward, who is general manager operations/technical & supply with Qatar's GTL partner Shell Aviation. "The fuel is purely paraffinic - it has no aromatics - so it burns with no soot."

This means it produces less particulate matter, which reduces sulphur dioxide emissions.

The GTL kerosene is also expected to provide up to 5% higher energy density per weight. "This could enable aircraft to carry less weight of fuel to cover the same distance," says Woodward.

The actual mix of GTL and oil based kerosene will be determined following ground and flight trials being undertaken in conjunction with Delft University of the Netherlands, says Woodward. "The blend could be anything from 20% up to 50%, it depends on where we see the optimum return for emissions."

Ground testing of a Pratt & Whitney engine is underway in the Netherlands and flight-tests, using Delft's fully instrumented Cessna Citation, are due to start in a couple of months. "This will help us work out the sweet spot for the GTL blend," he says, adding that results are expected over the next 12 months.

During the London-Doha flight, two Qatar Airways performance engineers monitored the parameters from the A340-600's cockpit measuring fuel flow, exhaust gas temperature etc at different stages of the journey. Readings were taken once parameters stabilised in level flight as the aircraft was step-climbed from 29,000ft (8,850m) to 41,000ft. The results are being benchmarked against data from a regular London-Doha A340 flight fuelled with conventional kerosene.

Prior to the 6h demonstration flight, the A340 was defueled to ensure that an exact 50/50 blend was uploaded. As GTL kerosene is a "drop-in" fuel, after the flight the tanks could be topped up with normal kerosene without the being defueled again.

The demonstration flight took off with an uplift of 90,000 litres of GTL blend Jet A1 with 240 passengers on board at a take-off weight of 284t. The only significant divergence from normal operations was the requirement not to use the auxiliary power unit as it was not cleared for the GTL fuel.