Emission control

UK collaboration could lead to a car exhaust trap that is able to reduce pollutants and provide an onboard fuel source. Siobhan Wagner reports

An exhaust gas trap that breaks down pollutants from diesel engines into hydrogen and carbon monoxide that can be injected back into the engine to provide a valuable fuel mixture could also reduce fuel consumption and emissions.

The technology, being developed by engineers at Birmingham and Brunel universities, is still in its early research stage, but the team hopes to demonstrate a full working prototype in 18 months.

Environmental catalyst manufacturer Johnson Matthey is collaborating on the project to develop a trap that will use a rhodium-based catalyst to extract essential compounds from car exhaust gas and convert them into hydrogen and carbon monoxide.

Birmingham’s Athanasios Tsolakis, the project’s principal investigator, said there are other research groups currently looking to reform car exhaust gas for onboard hydrogen production, but claimed his technology is simpler than other systems.

Unlike other methods, he said, his team’s unique catalyst-based system does not require additional air and water (or steam) for the reforming process.

‘We need oxygen, water, carbon dioxide and heat for this process and enough of those things for our reformer are contained in exhaust gas,’ said Tsolakis. ‘So the main advantage is you don’t need a lot of hardware, as is the case with other methods.’

The Birmingham and Brunel team has ambitious emissions reduction goals for its system, which combines a diesel particulate filter and catalytic reforming technology. The researchers hope to achieve a more than 90 per cent reduction in hydrocarbon, carbon monoxide and particulate matter emissions and a more than 70 per cent reduction in nitrogen oxide (NOx) emissions.

The system would be a step beyond exhaust gas recirculation (EGR) a NOx emissions reduction technique used in many diesel and petrol engines. EGR pipes an engine’s exhaust gas from the exhaust manifold to the engine’s inlet manifold. When in the combustion chamber, the recirculated exhaust gas absorbs heat and therefore lowers peak combustion temperatures. These lowered temperatures lead to a decreased production of NOx because the compound increases formation at higher temperatures.

The hydrogen produced with the new catalytic reformer will also reduce NOx produced in the combustion chamber. Hydrogen has a wide flammability range and therefore allows for lower combustion temperatures. When combined with carbon monoxide it has the dual advantage of being used as a secondary fuel.

Tsolakis believes that valve and fuel injection timing could be redesigned in diesel engines so that they could take in both diesel and hydrogen/carbon monoxide fuel.

‘When the hydrogen and carbon monoxide burn in the engine, there will be a reduced amount of diesel fuel injected into the combustion chamber,’ he said. ‘So in a way the engine could work as a dual fuel engine.’

Tsolakis said that based on his group’s calculations, replacing diesel with hydrogen and carbon monoxide produced on board will lead to a 10 per cent improvement in fuel efficiency.

It is hoped the reforming technology could be improved in the future to produce even more onboard hydrogen, allowing cars to increase fuel efficiency further.