Tighter emission limits proposed for off-road engines

Substantial reductions in emissions of nitrogen oxides and particulates from construction equipment and other kinds of non-road mobile machinery would be required under legislative proposals published by the European Commission at the end of December.1 The measure would align EU with US emission standards - apart from one major unresolved issue about future technology for controlling NOx emissions.

Emissions from diesel engines used in non-road mobile machinery are currently being reduced in a two-stage programme due to be completed at the end of 2003. Introduced by a 1997 Directive, the programme will reduce emissions of NOx by around 40% and particulates by 60% compared with those from non-regulated engines.

However, with major emission improvements in the pipeline for on-road vehicles, the Commission estimates that the 1997 Directive will leave emissions from off-road machinery at roughly the same level as those from road transport by 2020 - and wants to harness the best available technology to drive down emissions from the off-road sector.

This will require a move beyond engine modifications to the use of add-on abatement technology. Under existing EU legislation for on-road vehicles, after-treatment devices to reduce emissions of particulates are likely to be required from 2005, and to control NOx emissions from heavier vehicles from 2008 - and it is these technologies which the Commission hopes to see deployed a little later in the off-road sector.

Under its proposals, the scope of the 1997 Directive would be extended to include engines used in inland waterway vessels and some railway locomotives. Tractor emissions are already controlled under separate legislation, and the Commission is planning a further proposal on emissions from shipping.

As now, the legislation would apply to engines with net power ratings of 19-560kW. Different emission limits would apply to engines in four bands within this group, and the tighter standards for NOx and particulates would be phased in in two stages, beginning at the end of 2006 and 2010.

In broad terms, the Commission is aiming for reductions beyond those required by the 1997 Directive of 80-90% in particulate emissions and 30-40% in NOx emissions. The NOx reductions would take effect from 2006, while the major cut in particulate emissions would be required from 2010.

However, because of uncertainties about the technical and economic practicability of using after-treatment devices developed for the on-road sector in off-road machinery, the Commission has proposed that some important decisions should be deferred to 2006.

A review in that year would consider the need to exempt some kinds of off-road machinery from the second-stage particulate limits or at least delay their application. It would also consider the feasibility of using after-treatment devices to curb NOx emissions in a further stage beyond 2010.

The NOx issue is the one major divide between the EU and US, which are striving to harmonise their emission standards so as to minimise costs to engine manufacturers. In the US, the Environmental Protection Agency sees NOx absorbers as the preferred technology of the future, whereas European manufacturers favour selective catalytic reduction (SCR) even though this will require periodic refills with urea - and a separate distribution system for the chemical.

The Commission warns: "The current strongly global approach [to future emission requirements] could be jeopardised if Europe favours technological development of SCR and the US opts for NOx absorbers."

The move to tighter particulate standards and after-treatment devices will also have implications for fuel quality - notably sulphur content.

The current sulphur limit for fuel used in off-road machinery is 2,000ppm, falling to 1,000ppm in 2008 - but this will need to be slashed to less than 50ppm when the second-stage standards for particulates take effect in 2010. The Commission says it will propose an amending Directive to that effect - a move which could have implications for Member States which currently allow low-taxed heating oil to be used as fuel in off-road machinery.

Other elements of the draft legislation would provide "flexibilities" for equipment manufacturers to continue using "old" engines for a period beyond the deadlines laid down. There will also be a new transient test cycle for measuring particulate emissions from engines to reflect their variability during actual operation.

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