UK-based global major power and propulsion systems group Rolls-Royce has announced that it has had a successful start to the final stage of testing of its Advanced Low Emissions Combustion System (ALECSys). This is the flight test stage. The ALECSys demonstrator engine has been fitted to the group’s own flying test bed aircraft, a modified Boeing 747. The flight tests are being conducted in the US, from Tucson, in the State of Arizona.

ALECSys is a new-generation lean-burn combustion system for turbofan engines. It ensures better pre-mixing of the fuel and air, before the mix is ignited. That results in the combustion of the fuel being cleaner, reducing both nitrogen oxide and particulate emissions.

The demonstrator engine has already undergone a comprehensive series of ground tests. These included running on 100% sustainable aviation fuels (SAF), ground operability, emissions, water ingestion and icing.

“We are very pleased to see the ALECSys engine now flying,” affirmed Rolls-Royce Civil Aerospace product development and technology director Simon Burr. “This flight testing is a key part of our drive to not only improve engine efficiency but all aspects of environmental performance. It is part of the wider Rolls-Royce sustainability strategy, which also includes support for the increased use of [SAF] and intensive research into alternative propulsion architectures and technologies.”

So far, the flight test programme has seen the engine operate at 40 000 feet, or about 12 200 m. (Airliners normally fly at altitudes between 9 400 m and 11 600 m.) It has also involved the engine being switched off and then ‘relighted’, a number of times, at different altitudes and in different conditions. All these relights were successful.

“The ability to test ALECSys’ low-emissions technology in flight will allow the verification of altitude operability performance and provides experience of operating a lean-burn system to maximise maturity ahead of a future entry into service,” explained Rolls-Royce. ALECSys is an element in the group’s UltraFan programme, which is developing a demonstrator engine that will reduce fuel consumption by 25%, in comparison to the first generation of the company’s Trent family of engines.

ALECSys is being supported by both the UK and the European Union (EU). This support is channelled through the EU Clean Sky programme, the UK Aerospace Technology Institute and Innovate UK.