Emission Technology for cars (EGR, SCR, LNT)

For passenger cars and delivery vans there are three main technologies available for the reduction of NOx emissions. These technologies are EGR (Exhaust Gas Recirculation), LNT (Lean NOx Trap) and SCR (Selective Catalyst Reduction). The SCR-technology uses AdBlue as an NOx reduction fluid.  

What is EGR?

EGR works by recirculating a portion of an engine's exhaust gas back to the engine cylinders. The nitro oxide (NOₓ) emissions will be reduced since NOₓ is usually formed when a mixture of nitrogen and oxygen is subjected to a high temperature. Because of this EGR-technology the NOₓ emission is reduced by up to 30%.  The EGR technology has a large impact on the needed cooling capacity of the cars, as the high temperature exhaust gasses needs to be cooled down before mixed with the inlet air.

What is LNT ?

LNT is a technique which absorbs NOx, and when almost full the Lean Nox Trap needs to regenerate itself (it needs to clean itself) and it uses extra fuel for this process.  This technique is mostly used on smaller cars, these needs less often regeneration and therefore this has little influence on the fuel economy. On large cars on the other hand, this technique would cause quite an impact on the fuel economy of the car, which makes the car quite more expensive in daily use and more expensive to purchase due to the tax regulations. Large cars use there for the SCR-technology.

What is SCR?

SCR-technology uses and catalyst and AdBlue to reduces the NOₓ emission by converting NOₓ  into less harmful nitrogen and water vapor. AdBlue is injected into the exhaust where it vaporizes and mixes with the exhaust gasses, this mixture enters the SCR where it reacts, and converts the NOx.

Future legislation, Real Driving Emission (RDE) for cars

Almost all modern engines are tested according to the accepted testing protocols in a laboratory, where they have the ideal set up for the test and produce relatively low emissions well within the set standards. Usually only a one or a several engines from a series are tested as they are supposed to be identical. Now tests show that these laboratory tests may not be that accurate and that there is a difference between the lab results and the results in real life.

  1. The bulk of the total emissions can come from relatively short high-emissions episodes

  2. Emissions characteristics can be different even among otherwise identical engines

  3. Emissions outside of the bounds of the laboratory test procedures are often higher than under the operating and ambient conditions comparable to those during laboratory testing

  4. Emissions deteriorate significantly over the useful life of the vehicles

  5. There are large variances among the deterioration rates, with the high emissions rates often attributable to various mechanical malfunctions

The European Commission reacted to this problem by introducing mandatory test procedures for light duty vehicles (vans and cars). These real driving emissions (RDE) are measured by a portable emission measurement system (PEMS).

PEMS is essentially a lightweight, portable ‘laboratory’ which can be carried from one jobsite to another. Because PEMS is not bound to one testing facility it’s easy to use for ‘real-world’ testing. This does often raise one important question: as PEMS is limited in size, weight and power consumption can PEMS offer the same accuracy and variety of test results as would be possible with top of the line laboratory equipment?

This question cannot really be answered objectively and researchers should always keep in mind almost each test has its errors, like vehicle-to-vehicle differences or emission variability within the vehicle itself. To come to more accurate results, researchers should consider:

1.The difference between what is measured and what is actually emitted during a test

2.The difference between what is emitted during the test and what the vehicle emits during its everyday duties

3.The difference between the emissions characteristics of the tested vehicle and the overall emissions levels of the entire fleet.

This new procedure with PEMS implies challenges for original equipment manufacturers since exhaust control systems must perform under a broad range of different operating conditions. The limitation of RDE will be a part of the EU6c Emissions Regulation for Passenger Cars in Europe in 2017.

Euro 1 to Euro 6

Euro 1 – 5

Cars and commercial vehicles sold in Europe are subject to strict limits on the emission. These limits are referred to as ‘Euro’ standards, which were introduced in 1991 with Euro 0 for passenger cars. Emission standards did exist before Euro 0, but this was taken as the starting point for Euro standard references.

To reduce emission the European Union enforced Euro 1 for cars in 1993. It was setting emission standards for commercial vehicles and light trucks. It was the start of a step by step reduction of emissions from all engines to improve air quality in Europe. Euro 1 was soon followed by Euro 2 for cars in 1996, which included legislation for motorcycles.

Euro 3 was introduced in the EU in 1999 and limited diesel car emissions. Euro 4 for cars was introduced in 2005 and proposed further limiting of petrol and diesel vehicles emissions.

In 2009 Euro 5 for cars came in to force. It proposes to limit harmful emission from diesel engines. The focus is mainly to reduce the emission of nitrogen oxides (NOₓ) by 20% and particulate matter (PM) by 80% of diesel powered vehicles. Most commercial vehicle manufacturers resorted to direct injection engines and diesel particulate filters (DPFs) or the Selective Catalyst Reduction-system (SCR) to meet the emission standards.

Euro 6 for cars is the strictest European emission standard up to now. It will especially affect standards for diesel driven vehicles. Compared to Euro 5, Euro 6 focusses mostly on two types of emission: nitro oxide (NOₓ) and particulate matter (PM). Euro 6 requires passenger cars to reduces the NOₓ emission by 50% compared to Euro 5, which can only be done through SCR-technology, LNT, and the usage of a Diesel Exhaust Fluid (like AdBlue). Euro 6 for passengers cars is effective from 1 September 2014 for type approval vehicles and from 1 September 2015 for registration and new vehicle types. Most modern diesel powered cars with an engine capacity of 1.6 and more will start using SCR technology and AdBlue as emission reduction fluid in 2015.

History and levels of Euro standards for passenger cars you can see on the second picture.


Emission legislation

Every year, emissions legislation for combustion engines becomes more and more stringent. The emission of NOx is further limited in Euro 6 legislation. For larger cars, the only way to achieve this reduction is to have an active NOx reduction system on board. Virtually all passenger car and delivery van manufacturers have opted for the proven SCR technology which uses AdBlue as a reduction fluid.

In this section we provide you with more information about the Euro 1 to Euro 6 emissions legislation, and about possible future legislation for cars.