Piezo fuel injectors may improve aircraft efficiency

Researchers at Bath University are developing technology for more efficient ‘lean burn’ aircraft engines that will have a lower environmental impact, thereby helping to meet emissions targets for the airline industry.

Part of the technology will use piezoelectric actuators to more precisely control fuel valves and overall engine performance.

The project will be undertaken by the centre for power transmission and motion control (PTMC) at Bath’s department of mechanical engineering, with industry assistance from Aero Engine Controls (AEC) — which itself is a joint venture between Rolls-Royce and Goodrich.  

In June 2009 the International Air Transport Association (IATA), the trade group for airlines, set targets for its members to achieve an average improvement in fuel efficiency of 1.5 per cent annually from 2009 to 2020 and a reduction in CO2 emissions of 50 per cent by 2050, relative to 2005 levels. It also called for a cap on aviation CO2 emissions from 2020 (carbon-neutral growth). 

Although more radical aircraft design and propulsion is being considered, in the medium term one way of achieving targets is to make current engines more efficient. 

’We’re looking at new fuel-valve technology. Combustion within the aero engine doesn’t happen in a homogenous way throughout the whole engine; if you can control individual injectors you can control the combustion in a much more efficient way,’ said Prof Andrew Plummer, director of the PTMC at Bath. 

One way to do this might be through piezoelectric drives, which contain special crystals or ceramics that expand upon the application of an electrical field. Compared with electro-hydraulic systems traditionally used in valves these promise to be more efficient and precise.

Delphi, a global supplier of electronics for the automotive sector, has been commercially producing ‘piezo injectors’ for diesel engines for around two years now, with a claimed reduction in emissions, greater torque and improved fuel economy.

However, piezoelectric drives for aircraft engines present a much more difficult undertaking.

’One of the issues is the conditions; these things are likely to be mounted very close to the combustion chambers, so the temperature and vibration environment is very challenging. In addition, being an aerospace application, in terms of the reliability requirements, you’ve got to be able to prove these things will fail only once in so many million hours,’ Plummer said.

With the IATA’s targets in mind, he hopes that commercialisation of the valve technology would be in place by 2020.