AT THE HEART OF THE ROAD TRANSPORT INDUSTRY.

Call our Sales Team on 0208 912 2120

I 1+1 PRAISE 0E..

24th February 2005
Page 62
Page 63
Page 62, 24th February 2005 — I 1+1 PRAISE 0E..
Close
Noticed an error?
If you've noticed an error in this article please click here to report it so we can fix it.

Which of the following most accurately describes the problem?

HYDROGEN

Hydrogen is now taking centre stage in the search for clean emissions — and not just as a fuel. John Kendall reviews the latest developments taking place in emissions controls.

Vehicles powered by hydrogen fuel cells are still many years from commercial reality. But as emissions regulations trogressively tighten, exhaust system and axle aanufacturer ArvinMeritor believes using tydrogen in diesel engines could simplify mission control systems within the next few 'ears. It also predicts that engines fuelled with i mixture of petrol and hydrogen will rival the :fficiency of diesels.

The key to both systems is a low-powered tlasma reformer system' which eliminates the teed for a separate hydrogen fuel supply.The plasma reformer produces hydrogen on lemand from the vehicle's fuel supply. vhether petrol or diesel, avoiding the weight nd cost of a separate supply system.

The plasma is similar to a strong continuous park ,which partially bums a mixture of air nd hydrocarbon fuel. By design there is not nough air in the mixture to support combusion; instead the fuel/air mix breaks down to form a hydrogen-rich gas. In a diesel engine, this hydrogen rich fuel can be used to help regenerate exhaust emissions equipment.

The plasma reformer uses about 100W of energy — the equivalent of a pair of conventional headlamps.

Traditional problem

Future emissions limits will dramatically reduce the amount of particulate matter (PM) or soot and oxides of nitrogen (NOx) permitted in diesel exhaust.The traditional problem is that measures used to reduce one of these tend to increase the amount of the other.

To meet the Euro-4 limits that come into force next year most European truck manufacturers have resorted to designing engines that produce far less PM, then using selective catalytic reduction (SCR) to reduce NOx in the exhaust stream. This will need the urea additive AdBlue to reduce the NOx in the catalytic converter. AdBlue is also necessary to remove sulphur which would otherwise reduce the active life of the catalyst material considerably. While using ultra-low-sulphur fuel helps, it normally requires temperatures of 600-700'C to ensure removal of the sulphur — but this can also destroy the catalyst.

The alternative Euro-4 strategy is the route chosen by MAN and Scania. Here NOx production is reduced by cooling the exhaust gases and recirculating them through the engine to bum the partially combusted fuel more completely.The PM is then collected in a particulate filter, which needs to be regenerated continuously. If not,the filter would simply clog up with soot and the engine would stop working.

For regeneration the exhaust temperature is raised by injecting diesel into the exhaust stream, causing the soot particles to bum off harmlessly.

By introducing a plasma reformer into the exhaust stream, ArvinMeritor claims some significant advantages. Euro-5, due around 2010, will bring even more stringent limits and new challenges; the plasma reformer could help to tackle these tighter limits too.

ArvinMeritor has carried out research into plasma reformers with systems designed to reduce both NOx and PM emissions. Significant benefits have been shown in both cases.

For NOx treatrnent,ArvinMeritoes research has focused on applying the plasma technology to a 'dual leg NOx trap' as opposed to an SCR system.The plasma reformer is fitted at the inlet end of the NOx trap before the gases pass into one leg or the other—the dual-leg design means exhaust can be treated by one leg while the other is being regenerated.

Experiments have shown hydrogen can reduce the NOx stored in the trap by more than 90%. far more effective than Euro-4 SCR systems.Another advantage is that no additive is required — a considerable attraction for vehicle manufacturers and operators, as removing the additive tank and dosing system would save weight and possibly cost.

As far as operating temperatures are concerned, the plasma reformer can remove sulphur at temperatures as low as 400°C — roughly the temperature of conventional diesel exhaust.And NOx removal is effective at temperatures down to 150°C.

Effective removal

Applying the plasma technology to a combined oxidation catalyst and particulate filter, ArvinMeritor has seen the hydrogen gas mixture react on the oxidation catalyst at exhaust temperatures as low as 100°C.This indicates that it may be effective even at 'cool engine temperatures'.

Compared with current methods of filter regeneration, using diesel fuel to raise the filter temperature, the plasma system uses 20% less oxygen from the exhaust for the same energy release. The system does not need the diesel exhaust injection sequenc,e, triggered by the engine control electronics, as the plasma is operated independently.

If either technology proves viable it could have a considerable impact on emissions control systems, raising the possibility of simplifying them and reducing cost. It remains to be seen if the two systems could work in tandem to reduce PM and NOx using the plasma reformer. If so, this could be of considerable interest as we move to Euro-4 and beyond.

ArvinMeritor also reports the plasma reformer works well with the advanced homogenous charge combustion ignition (HCCT) diesel technology, which Ishows promise for simultaneously reducing PM and NOx. Plasma reformer technology could be commercially viable by 2009, but the company believes HCCI is unlikely to arrive before 2014. •

Tags

People: John Kendall

comments powered by Disqus