Fired up for the future

The glamour of the fuel cell is keeping a credible rival out of the spotlight — the homogeneous charge compression ignition (HCCI) internal combustion engine. Manufacturers are spending millions of pounds researching this technology because it promises to be cleaner than conventional diesels and more efficient than petrol engines.

It is a relatively old combustion technology that has been left idling for decades. The race is now on to get it into production because it can use fuels that are easily available, so no new infrastructure is needed.

More funding

Dr Zhijun Peng in the engineering department at Sussex University believes in the future of HCCI. He has been awarded almost £200,000 to fund 27 months’ research into improving the control of the technology.

It is not just the government’s Engineering and Physical Sciences Research Council that thinks his endeavours worth supporting. Diesel engine manufacturer Caterpillar is contributing to the project and BP is also backing him. More funding from the DTI is already on stream.

‘By the end of 2008 we hope to have a working prototype engine,’ said Peng. ‘Then the next step will be the pre-commercial development of production versions.’

Although The Wall Street Journal reported last October that Honda could launch an HCCI in an electric-diesel hybrid some time this year, nothing has yet emerged and the Japanese company will only say it is working on it. So are most other leading manufacturers, and production is not expected to begin anywhere within five to 10 years.

Peng began his work on HCCI at Brunel University in 1998. The technology contains elements of a conventional spark-ignition internal combustion engine (ICE) and of a compression diesel ICE, yet eliminates many of the problems associated with both.

It has no spark plug and the mixture of fuel and air combusts spontaneously and homogeneously when compressed. Unlike a conventional diesel engine, there is no need for fuel injection to trigger combustion and, as ignition begins at many points simultaneously throughout the mixture, little fuel is left unburnt.

This is good news for emissions. With homogeneous combustion, there are few particulates and with significantly lower peak temperatures, oxides of nitrogen levels are negligible. The lean mixture makes it more efficient than a petrol ICE and it runs without throttle so there are no throttling losses.

Challenges to overcome

Despite the technology’s potential there are challenges that Peng and others must overcome to make HCCI work in the real world as well as on the test rigs. ‘We must get the right temperature and pressure for combustion to take place,’ he said. ‘We have to get a high load and avoid knocking. And we have to look at how we can start the engine, particularly from cold.’

One aspect is to consider starting a petrol-fuelled engine in a conventional manner, with spark ignition, but then go through a transition to sparkless HCCI. Managing the transition is being studied.

There are several ways combustion can be controlled, including two that Peng is studying — injection control, variable valve actuation and variable valve timing. He is looking at a control model that co-ordinates the two so they work together to control the internal exhaust gas recirculation.

HCCI, if made to work smoothly, should allow vehicle engines to meet ever-tighter emissions targets for years to come, particularly when combined with the correct catalysts to deal with the increased carbon monoxide and hydrocarbon emissions. And the fact that all vehicles will be able to continue to use familiar filling station fuels gives the technology an edge.

A likely formation is for HCCI engines to be used in hybrid vehicles because the technology works best at a constant level of output. But its future would still depend on a secure supply of petrol and diesel — things that a fuel cell does not need.