Hot work

Rolls-Royce and Cambridge University aim to develop laser sensors able to monitor the internal performance of industrial-scale fuel cells.

Engineers developing the ‘wavelength-agile’ sensors plan to use advanced-fibre laser technology to enable wide-spectrum measurement of the complex physical and chemical conditions within fuel cells or combustion engines.

The ability to characterise the composition and temperature of burning gases inside operational fuel cells could prove invaluable in the development of a new generation of large-scale devices, according to Rolls-Royce Fuel Cell Systems, which will work with Cambridge’s department of chemical engineering on the five-year, government-backed project.

According to Dr Johan Hult, project leader at Cambridge, making the laser sensor system durable enough to withstand the extremely high temperatures encountered in fuel cells and engines will represent a key challenge. Hult said the project team is investigating using fibres made from sapphire, which should be robust enough to survive the intense heat.

In the system being developed, a fibre laser emits short pulses of less than one-trillionth of a second at a rate of 100million times per second. The spectral range of the laser is widened by the use of crystal fibres and a high-dispersion fibre ensures a rapid wavelength sweep.

The resulting absorption is recorded using a photodiode and an oscilloscope, which calculate the gas composition and temperature. The lasers will be able to monitor a wide enough spectrum inside a fuel cell to allow simultaneous detection of a variety of hydrocarbons.

These optical laser sensors differ in crucial respects from those used to monitor diesel engines. Conventional laser sensor systems use diode lasers that are cheap but which only operate over a small spectrum. The fibre lasers that Hult’s team propose to use scan over a range of 100nm, which allows the detection of a wide range of fuel species and has the advantage of dealing with the effects of background infrared interference.

Hult said: ‘Inside the fuel cells, the laser will pick up a great deal of background infrared radiation from the red-hot cell walls. Because a fibre laser detects over a wide range, the effects of the background radiation can be effectively cancelled out.’

Rolls-Royce Fuel Cell Systems, a division of the UK engineering group researching commercial solid oxide fuel cell (SOFC) technology, has high hopes for the sensors. After initial tests at the university, the team will use Rolls-Royce’s own fuel cells for more detailed analysis of the technology.

A spokesman said: ‘This technology will look at fuel composition within operating products in real time, rather than us having to estimate what is going on inside. We have an interest in helping make this technology work, because we believe it will add a diagnostic capability for gas turbines and fuel cells which does not currently exist.’

• US power giant GE Energy plans to develop a 100MW fuel cell power plant to be fuelled by coal. The US Department of Energy has awarded GE Energy’s Hybrid Power Generation Systems division an $83m contract to design the plant to maximise the efficiency of SOFC technology. The programme’s objectives are to design the plant and a proof-of-concept system incorporating a hybrid SOFC/gas turbine that can achieve more than 50 per cent efficiency from coal. Existing conventional coal-fired power plants operate at about 35 per cent efficiency.