JAGUAR. Diesel or Petrol?

Date posted: 13 February 2018

Industry News

Should I choose petrol or diesel car?

Changes in legislation, concerns over public health and the transparency of emissions testing, has caused many to question how clean diesel engines are and whether it’s the right choice for them.

It is important to note that current diesel engines are some of the cleanest ever produced. 

New laboratory testing methods and procedures (WLTP) introduced in September 2017 will result in official fuel economy and CO2 emissions that more closely match real world figures. At the same time, a new emission standard (EU6d RDE) will see cars tested on the road – as well as in a laboratory – for the very first time, allowing for even greater transparency and accuracy in emission figures. 

Diesel engines were widely promoted by the government in recent years as they emit on average 20-25% less CO2 emissions than their petrol counterparts, however this view has seen a shift following more awareness on NOx pollution.

Why are diesel engines under the spotlight? 

Oxides of Nitrogen (NO and NO2) are produced as a by-product of internal combustion (in engines). These Oxides of Nitrogen – NOx gases as they are known – and related hydrocarbons and other pollutants have been linked to respiratory problems, smog and poor air quality. 

Whilst diesels produce less CO2 on average than petrol engines, they produce more NOx. In modern diesels, Diesel Exhaust Fluid (DEF) – also known as AdBlue – is used within a Selective Catalytic Reduction (SCR) system to convert NOx back to Nitrogen and Oxygen. Older diesels, built before the latest EU6 emission standards were introduced, can produce much more NOx and particulates than the EU6 diesels, as they do not have this SCR technology. In addition, since 2006 Jaguar Land Rover diesel vehicles have been fitted with particulate filters, removing 99% of all particulates from the exhaust. 

Due to the impact on public health, a number of cities in the UK have subsequently announced measures to try to reduce NOx pollution. London for example, has introduced the ‘T-Charge’, an additional fee on top of the pre-existing congestion charge to discourage older diesel vehicles from entering certain areas. This legislation will be replaced in 2019 by a more permanent Ultra Low Emission Zone. EU6 diesel vehicles are exempt from this charge due to their low NOx emissions. 

Despite the recent criticism of diesel cars, The Society of Motor Manufacturers and Traders (SMMT) estimates that cars on the road only account for 14% of the nation’s NOx emissions, and that it would take four times the number of EU6 diesel cars currently on the road, to generate the same amount of NOx as one UK coal-fired power station. 

Jaguar Land Rover’s commitment to sustainable driving however, means we are pro-actively producing some of our cleanest engines to date, dramatically reducing our NOx emissions and removing the need to compromise a cleaner choice of vehicle for one with a defined performance. 

  • From September 2015, all of our diesel engines built for the EU and EEA markets, are fitted with Selective Catalytic Reduction treatment which uses the urea-based liquid AdBlue, to convert Nitrogen Dioxide into Nitrogen, Oxygen and water. This exhaust after-treatment converts up to 98% of NOx gases produced by diesel engines, meaning a significantly reduced impact on the environment.
  • Filtering technology fitted as standard to all of our diesels, removes up to 99% of all soot particles before they leave the exhaust. The Diesel Particulate Filter does this by extracting and storing particles until they are burnt away automatically and the filter is emptied.
  • All of our EU and EEA diesel engines from September 2015 meet tough EU6 emissions regulations, meaning they are so clean they can pass freely through the Ultra Low Emission Zones that will enforce a financial penalty on drivers emitting high levels of pollutants from their vehicles.

What’s the difference between Petrol and Diesel? 

Diesel cars deliver an effortless, relaxing drive because of low-speed torque. The narrow power band allows you to change up through the gears earlier and generate meaningful acceleration, making activities such as towing or carrying a large number of passengers much easier. 

There has been a misconception that diesel engines are slower, noisier and more expensive to run than petrol vehicles. However engineering advancements and technologies now in-built in diesel engines, means the difference between the two is now barely identifiable. 

The widely spread power band in a petrol engine typically requires higher engine speeds to deliver similar torque as a diesel, but the top-end power of a petrol offers a smooth and responsive drive which some drivers prefer.

Which engine is right for me? 

Before purchasing any vehicle, you should take into consideration your usual driving habits. Diesels come into their own on longer journeys at higher speeds, but aren’t necessarily the best choice if your usual drive consists of shorter journeys or regular stopping and starting while held up in traffic in a town or city. 

If you are driving 12,000 miles a year or more, a diesel is likely to be the most cost-effective choice. The higher energy density of the fuel and the way energy is released during combustion, means diesel can offer a greater return on mileage. 

The Diesel Particulate Filter (DPF) that collects soot particles in the exhaust and prevents them entering the atmosphere, requires the exhaust to reach a sufficiently high temperature - achieved through driving at a sustained speed and distance - to burn off the collected contaminants. 

If this is not a likely occurrence in your day-to-day driving, and travel tends to consists of short sharp bursts of acceleration and braking, a petrol or hybrid engine may be a better choice for you.

How will changes in legislation around diesel affect me? 

Diesel cars driven in urban areas are likely to incur additional costs over the coming two or three years, over and above those imposed on petrol or alternative fuelled vehicles, an example of which, being the previously mentioned, T-Charge. 

However, owners of newer diesel vehicles which meet the latest EU6 emissions standards will not be penalised in the same way as older less environmentally-friendly diesel vehicles. 

All of our diesel vehicles sold since September 2015 in the EU and EEA markets, meet these EU6 standards. 

Ultimately, the decision you make when it comes to buying diesel or petrol is down to you. Factors such as regular journey type, where you drive and the type of vehicle will be the biggest considerations. 

When it comes to considering the environmental effects when making your choice, modern technology means the impact of emissions from diesel and petrol are lower than ever before.

The results so far 

Jaguar Land Rover has invested £1 billion at our state-of-the art engine manufacturing centre to develop smaller, lower emission diesel engines. 

These developments have yielded remarkable results; between 2007 and 2015 we’ve reduced the CO2 emissions from our European fleet vehicles by 32%. 

In addition, between 2004 and 2016, our expert engineers have managed to reduce our NOx emissions by 90%.


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