Environmental exhaust emissions

25 April 2006

Adam Gristwood, Editor of Freight Transport Review, examines the use of SCR technology in reducing HGV emissions.

The European emission regulations for heavy goods vehicles, particularly Euro IV and the forthcoming Euro V, are having a significant impact on HGV fleets across Europe, with fleet owners working hard to bring their operations into line with these stringent rules. The adoption of emissions reducing technology for all new registered trucks is inevitable – after October 2006 for Euro IV and October 2008 for Euro V. But they are justified rules, and Europe is a world leader in environmental matters, demonstrating great commitment in adopting and enforcing legislation designed to protect the environment. In emerging market economies, the difficulties associated with adhering to the Euro rules, such as cost and technological lag, are magnified, as firms operating within less assured and lucrative markets struggle to keep pace and competitive margins with more established, 'Old-Europe' nations.

Bringing HGVs into line with the Euro standards is an expensive business, particularly in nations where emissions standards have, in the past, been lax or poorly policed. As the European Union expands, and road hauliers from Accession States begin to enjoy the fruits of improved access to the biggest markets, the decision is already made to bring vehicles up to scratch and to have them running.

There are a number of options available to haulage firms in reducing their emissions in line with the Euro regulations, of varying expense and complexity, the two most common being Exhaust Gas Recirculation (EGR) and Selective Catalytic Reduction (SCR). Selective Catalytic Reduction is being widely adopted by hauliers across the continent as a cost-effective means of reducing environmentally damaging exhaust emissions, finding popularity amongst the major engine manufacturers.

How it works
SCR technology focuses on removing the various nitrogen oxides, the most environmentally unfriendly by-products of combustion, from exhaust gases. SCR was first trialled on large-scale projects – power stations and ship engines – before being fitted to larger diesel engines in road vehicles, with such success that it is now fitted to the majority of European HGVs. The science is (mercifully) simple: a gaseous or liquid reductant (normally ammonia or urea) is added to the exhaust gas stream and is absorbed onto a catalyst. The reductant reacts with the nitrogen oxides in the exhaust gas to form H2O and N2. The SCR reaction is fussy where temperature is concerned, occurring only within a small range, and SCR engines are designed to ensure that the temperature is maintained at an effective constant. In addition, specialist catalytic converters are required.

As a system that is still evolving, there are a number of debates around the best inputs and technologies for maximising SCR's benefits. Deciding between ammonia and urea continues to pose a challenging problem – ammonia is marginally more effective, but presents a far greater risk for those who handle it than the less efficient urea. Another important problem is the issue of ammonia slip – where reductant escapes through the exhaust pipe owing to an excessive input or to insufficient temperature – which presents a danger to anyone who might be exposed to the ammonia released.

Work is also still ongoing to improve the tuning of the SCR to an engine's operating cycle. Tuning is essential to the system, to ensure that maximum benefit is achieved, but assuring the uniformity of this good performance is currently posing a challenge to manufacturers, who have found it difficult to maintain optimum SCR function where even small alterations to the anticipated journey and loads of a vehicle can have a significant impact.

Nonetheless, despite these teething problems, this early stage SCR technology is already able to reduce nitrogen oxides in exhaust emissions by 85% and particulates by 40%.

An additional benefit to hauliers is a reduction in fuel consumption – vehicles employing SCR consume up to 5% less fuel than do Euro III vehicles. SCR allows diesel engine developers to calibrate their engines in a lower area of fuel consumption – the SCR technology removes the responsibility of the tuning and calibration of the engine itself to reduce nitrogen oxides and gives operators the flexibility to make their tunings in accordance with the performance criteria that they want.

SCR takes hold
EU Member States are allowed to use tax incentives in order to accelerate the adoption of vehicles that meet the new standards ahead of the regulatory deadlines. Such incentives are dependent on the meeting of the following criteria:
• That they apply to all new vehicles offered for sale on the market of a Member State, which complies in advance with the mandatory limit values established by the Directive;
• That they are discontinued when the new limits come into force; and
• That, for each type of vehicle, they do not exceed the additional cost of the technological solutions available to ensure compliance with the limits.

Early introduction of cleaner engines is also being stimulated by other financial incentives such as reductions in road tolls. In Germany, for example, road toll discounts have been introduced, which, in turn, has stimulated the market for Euro V-compliant HGVs.

Provision of the necessary additives – urea and ammonia – is also being broadened across the European Union and neighbouring countries. Reductants such as AdBlue, currently the leading brand amongst European hauliers, are receiving increasing support and coverage in filling stations, giving drivers and haulage firms fewer reasons to operate at variance with the European emissions standards.