Compress for success

The Turbo-Claw compressor is making PEMFCs a more viable fuel source for automotive applications

A new design for a Proton Exchange Membrane Fuel Cell (PEMFC) auxiliary component could make the technology less expensive to mass produce for cars.

PEMFC is viewed as a promising power source for automotive applications because its low-temperature working conditions allow it to start faster than those technologies using high-temperature fuel cells. The high power-density of a PEMFC also makes it an easy fit for the limited space available in a car.

The technology’s market acceptance has been hindered, however, by the high cost, mass and noise of a PEMFC’s auxiliary systems.

One critical part is the Air Management System. This uses an air compressor to transfer oxygen from the outside environment to the fuel cell, where it oxidises hydrogen into H2O.

Dynamic Boosting Systems, an Imperial College spin-out, claims to have developed a cheaper, smaller and quieter alternative to traditional compressors used for the job. The technology is scheduled for commercialisation in 2010.

The company’s patented TurboClaw turbo-compressor is based on a forward-swept rotor blade design, differing from most conventional turbomachines with back-swept rotor blades.

This means the blades spin quieter and at a much slower speed, explained Shahram Etemad, director of Dynamic Boosting Systems. The slower speed puts less mechanical stress on the machine’s motor, drive and bearings — reducing the cost of their design and increasing their reliability.

‘Any turbomachinery expert you speak to will say a forward sweep design does not work,’ he said, ‘but our patented design makes it work.’

Etemad added that conventional turbomachines are efficient, but their high operating speeds make them undesirable for mobile fuel-cell applications such as cars. This is why many have looked to less desirable alternatives such as positive-displacement machines, which are typically roots or screw compressors.

‘These are readily available and can be motor driven at low speeds, but have problems of high cost and noise,’ he said. ‘The double screw requires complex 3D shapes to be ground to an accuracy of a few microns. Screw superchargers have been available for automotive use for some time, but cost has been prohibitive for all but the least cost-sensitive applications. Roots superchargers are more common as they are cheaper, but less efficient. Noise is also a problem as a result of the timing gears.’

Also, unlike turbo-compressors, positive-displacement machines cannot be combined with turbo-expanders. Those devices are designed to recoup energy from the fuel-cell exhaust to reduce the amount of energy required to power the compressor.

Dynamic Boosting Systems is one of several companies selected by the Technology Strategy Board (TSB) to take part in a £10m R&D programme focusing on fuel cell and hydrogen technologies. The fund aims to encourage outside industrial partners to collaborate with companies such as Dynamic Boosting Systems and help bring their technology to the commercial stage.

Etemad said his company is already working with a variety of end-user partners for applications in the automotive industry and beyond. He suggested the compressor could be used for emergency power units and even domestic CHP (combined heat and power) units one day.

‘We will have evaluation units available this year,’ he added. ‘In 2010 we will see our first production units in the field.’

Siobhan Wagner