A Comprehensive Guide to The Emission of a Diesel Engine

Ian Lewis[1]

Ian Lewis

Money Savings Advice Diesel emissions explained

A diesel engine produces emissions in the form of nitrogen oxide. These are a byproduct of combustion. Diesel emissions can be toxic, so they’re carefully limited. Cars must meet standards for emissions of diesel engines in the UK and Europe.

The emissions of diesel engines are produced whenever diesel fuel is burned. If too many emissions escape into the atmosphere, they can harm people and the planet. Vehicle emissions must be kept in check to avoid high levels of pollution.

As a result, diesel cars must go through emissions testing. If a car produces high levels of emissions, it won’t pass current stringent diesel emissions tests.

Keep reading to learn more about the emissions of diesel engines in cars.

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Understanding the Emission of a Diesel Engine

When diesel is burned, it produces a gas called nitrogen oxide that’s not needed. Nitrogen oxide is a byproduct of the combustion of diesel. Since it isn’t used by the car, nitrogen oxide becomes a waste product that needs to be removed from the vehicle.

Nitrogen oxide isn’t safe. High levels of this greenhouse gas can damage the ozone layer. Nitrogen oxide has also been linked to eye problems, respiratory problems and an increased risk of cancer. It’s known to play a part in the prevalence levels of childhood asthma and has been linked to some cases of premature death.

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UK and Europe Diesel Emissions Limits

Understandably, nitrogen oxide levels need to be kept in check. This means that the emission of a diesel engine must go through rigorous testing. In the UK and Europe, there are certain diesel emissions standards. Other countries can set their own limits at different levels.

The UK and European limits are set at 0.080g/km of nitrogen oxide from a vehicle. This is a limit that must be adhered to whether cars are idling or moving. Before a car is approved for sale, it must go through diesel emissions tests.

Of course, second-hand car sales often won’t go through these tests. That’s why it’s so important you do your research if you’re buying a second-hand diesel car, to check whether it has legal emission levels and if any necessary adjustments have been made.

Controlling the Emission of a Diesel Engine

Car manufacturers have a duty to limit the emissions of a diesel engine. It’s their job to design a car that won’t set free too much nitrogen oxide. There are several different ways that diesel engine emissions can be controlled within a vehicle.

One way to lower emissions is to burn the fuel at a lower temperature. A diesel engine working at high temperatures will produce more nitrogen oxide. In exchange for higher levels of emissions, you’ll get a car that’s more fuel-efficient and more powerful.

Vehicle manufacturers must balance car performance with levels of diesel emissions. Slightly lower combustion temperatures will do a lot to help the environment and to protect people’s health.

Manufacturers can also fit cars with all different types of diesel filters. These can be expensive and may need extra maintenance, but help to make vehicles safer. Diesel filters can do a lot to lower levels of nitrogen oxide.

One very effective type of diesel filter is Selective Catalytic Reduction (SCR). This can reduce levels of nitrogen oxide by up to 90%. These systems use Diesel Exhaust Fluid to convert nitrogen oxide into nitrogen, water and carbon dioxide, which are naturally found in the air. They dispose of most nitrogen oxide effectively.

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Higher Emissions of Diesel Engines

Whilst stringent tests should protect consumers from high levels of nitrogen oxide, it’s been true in the past that you may have breathed in much more nitrogen oxide than you should. In 2014, it was found that many cars had cheated their way through emissions tests. Indeed, over the past few years, most major motoring companies have been found to have been involved, including VolkswagenGeneral Motors and Nissan.

When Dieselgate became public knowledge, many people were shocked. They were finding, for the first time, that vehicle emissions were recorded wrong. Many cars were actually producing more diesel emissions than on paper, with higher levels of nitrogen oxide potentially causing health problems.

Car manufacturers had been manipulating the results of diesel emissions tests. They’d been using defeat devices to get their vehicles through tests. These pieces of software, installed in many cars, could identify when cars were being tested.

Temporarily, they’d improve diesel filtering and lower levels of nitrogen oxide. This would be enough to get cars through testing, though diesel emissions were at very different levels in real-world driving conditions. In fact, some cars produced 40% more nitrogen oxide than when tested.

The Technology Required to Lower Diesel Emissions

The technology required to lower diesel emissions can be expensive and hard to maintain. It can also be very cumbersome. To use SCR all the time, cars must receive regular top-ups of Diesel Exhaust Fluid. The fluid is carried in on-board tanks that will add a lot of weight to a car. 

Manufacturers found that they could use smaller tanks, and make the fluid last far longer, by only using SCR when their cars were under test conditions.

Manufacturers recognised that consumers want convenient cars with great performance. To lower the emissions of diesel engines, someone would have to make a sacrifice. Many manufacturers made the decision to cheat through tests to make their cars seem more appealing.

Today, diesel emissions tests are a lot more thorough than they were. It would be significantly harder for a car to manipulate results. Now, vehicles are tested in a wider range of real-world conditions. They’re driven for longer, at all different speeds, to check that diesel emissions are consistent.

Does Your Car Meet Diesel Emissions Standards?

If you’ve owned a diesel car, it may have been fitted with a defeat device that changed its behaviour for tests. Your car might have produced higher levels of nitrogen oxide when driven day-to-day.

To find out if your car was part of the diesel emissions scandal, search online for ‘diesel emissions [car manufacturer’s name]’. If there’s a recall, this will be easy to find. You’ll need your car’s VIN to check if it has been recalled.

Recalled cars will need to be adjusted in approved vehicle workshops. The car manufacturer must cover the cost of any changes that are made to your car. If there’s a defeat device in your vehicle, a recall should mean that it’s switched off. Again, be sure to check whether any vehicle you’re buying was part of a recall, and ask for evidence that the work has been carried out before you buy.

Compensation for Emissions of Diesel Engines

Many people are claiming compensation for the diesel emissions scandal. If you believe that you’ve been affected, it’s best to join a group action claim.

Several law firms are managing group action, representing many different claimants. By joining, you can be part of a compensation claim. If you’ve had a car that cheated emissions tests, you could be entitled to up to 100% of the original sale price. More likely, you’ll get between 25-75%.

Search online to see which law firms are advertising group action for diesel emissions compensation claims. There’s still time to join if you’d like some money back for a diesel vehicle you’ve owned.

Quick Diesel Emissions FAQs

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Money Savings Advice Author Ian Lewis

Ian Lewis

Ian Lewis is one of our specialist financial writers. Ian has over 15 years of financial writing experience, having worked for some of the largest financial publications in the UK covering topics from mortgages, equity release, loans and financial claims, to name a few.

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