Light goods vehicle exhaust emissions

Euro 6 standards for light duty engines will be introduced for manufacture from September 2014, and for new registrations from January 2015. Richard Smith looks at the implications for operators of light goods vehicles.


Light goods vehicles are those that can be driven on a category B car driving licence, ie those with a maximum gross weight of less than 3500kg. In 2011, almost 3.25 million such vehicles were licensed, split roughly equally between private and business keepers, although many of the privately registered ones are no doubt used for business by self-employed people. Nearly 95% of these vehicles are powered by diesel engines, a sharp contrast with the situation in 1994 (the earliest year in the DVLA data set) when the split was roughly 50:50.

Emission standards

The majority of light goods vehicles, whether petrol or diesel powered, have their engines classified as light duty engines and are subject to the same exhaust emissions standards as cars. The current standard for both manufacture and registration is Euro 5; Euro 6 standards will be introduced for manufacture from September 2014 and for new registrations from January 2015.

Heavy duty engines are classified as those fitted to vehicles over 2610kg maximum gross weight, so a proportion of light goods vehicles will be subject to the same heavy duty emissions standards as heavy goods vehicles. With effect from 31 December 2012, the standard for manufacture is Euro VI and this will apply to new registrations from 31 December 2013.

The use of Arabic numbers (eg Euro 5/6) relates to both petrol and diesel engines fitted to vehicles under 2610kg gross. Roman numerals (eg Euro V/VI) refer to vehicles over 2610kg.

With new registrations running at between 200,000 and 300,000 annually, the total number of light goods vehicles in use obviously consists of vehicles of all ages and emissions standards.

Low emission zones

In the UK there are low emission zones (LEZs) in Oxford, Norwich and London, although the Oxford and Norwich zones apply only to buses at present. The London zone covers the whole Greater London area, including the M4 and M1.

The minimum standard required for vehicles with a maximum gross weight between 1205kg and 3500kg is Euro 3. Also in scope are many double-cab pickups and light utility vehicles, although there are some exemptions; these are listed on the Transport for London website. Vehicles that do not comply with the minimum standard will have to pay a fine or, if paid in advance, a daily charge.

A number of other EU countries operate LEZs in certain cities and regions but only in Germany, Italy and Portugal do these apply to light goods vehicles, including those with petrol engines. The required standards vary from city to city and there is no opportunity to pay a daily charge to use vehicles that do not comply, just a fine.

Controlled emissions

The gaseous emissions controlled by regulations are carbon monoxide (CO), oxides of nitrogen (NOx), and unburnt hydrocarbons (HC). The main focus was initially on these elements because of the medical evidence linking them to heart and respiratory problems. For petrol engines, the limits easily have been met by the fitting of a three-way catalytic converter but, as the nature of combustion in a diesel engine is different, such exhaust gas after-treatment is not needed, and a diesel engine is also naturally more fuel efficient. Diesel engines were thus the preferred solution in the early days of emission control and tax on diesel fuel was reduced to encourage their use.

Carbon dioxide (CO2) is not a pollutant and is an inescapable product of all combustion; in fact the better the combustion, the greater the proportion of CO2 that is produced. No limits are placed on CO2 emissions and the catalytic converter actually works by converting the regulated pollutants into CO2. The amount of CO2 produced by combustion is dependent on the amount of fuel that is burnt and, again, the better efficiency of the diesel engine helps limit the CO2, another factor in their favour once the alleged link between CO2 and supposed global warming came to be accepted.

However, diesel engines also produce carbon particulate matter (PM), which is also a concern as these particles can lodge in the lungs and cause problems, including cancers. Greater attention was thus paid to PM emissions from diesel engines and this has been the main concern in recent emissions legislation. Duty on diesel fuel has also been increased above that for petrol.

Diesel particulate filters

The only way to meet the PM limits for diesel engines (and LEZs) is by the fitting of a diesel particulate filter (DPF) as an after-treatment device, in a similar way to the catalytic converter for petrol engines. The DPF traps the carbon particles in the exhaust but, as with any filter, it will eventually become blocked. To clear the filter, the trapped particles are periodically burned off at high temperature in a process known as “regeneration”. When the DPF is located close to the engine, where the exhaust gas is hotter, regeneration can take place passively during high-speed runs on the motorway but, if the vehicle does not get regular high-speed running, passive regeneration will not take place and the engine management system will initiate active regeneration by making adjustments to the fuel injection timing to increase the exhaust temperature. However, on short or stop-start journeys, the active regeneration process may not complete and the DPF warning light will come on. If the light is ignored, the filter will clog to a point where the engine management system will trigger a fault mode and the vehicle will have to be taken to a dealer for regeneration. In the worst case, this may require a new DPF at a cost of around £1000.

If the DPF cannot be fitted close enough to the engine for exhaust gas temperature alone to produce regeneration, a different system that relies on a fuel additive to lower the ignition temperature of the soot particles is used. This additive is stored in a separate tank and automatically mixed with the fuel when driving. Only a small amount is used and a litre of additive should be enough to treat about 2800 litres of fuel. When the tank is empty it will need to be replenished at a cost of up to £50. Driving without fluid in the tank will cause the DPF to clog, with the same effect as noted above. The latest Euro VI standard makes it an offence to drive without the fluid and it should therefore be included in the daily walk-round check.

Vehicle specification and use

Diesel engines are generally preferred for commercial use because of their longer life and better fuel consumption — both factors partially offset by the higher cost of the engine and the fuel. However, the problems caused by DPF failure to regenerate mean that diesel engines may no longer be a suitable option for light goods vehicles that are used mainly on short, stop-start runs in urban areas.

Active regeneration may typically take place about every 300 miles and take between 5 and 10 minutes to complete, during which time the engine will need to operate at a constant high speed. Once the DPF warning light comes on, regeneration should be able to be completed by an uninterrupted period of at least 40 minutes driving at a minimum of 40 mph. Regeneration may require driving in a lower gear than usual to ensure that the engine speed is high enough to produce sufficient exhaust gas temperature.

Unless the conditions required for regeneration of the DPF can be ensured, a petrol engine may well be the better option.