Should I buy diesel in light of changing government policy?

I am about to replace my car and would normally have gone for a diesel but I'm concerned that Government policy may be changing and make owning a diesel car increasingly more expensive so wonder whether a petrol engine may make more sense as I hope to keep the car for some time

Asked by Neil

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Government policy aimed at reducing energy consumption and CO2 emissions has tended to favour diesel over the past 15 years. The higher cost of diesel fuel and improvements in petrol engine technology have eroded some of diesel’s advantage and it can take a very long time to recoup the often higher initial purchase price of a diesel car.

Policy is also concerned with reducing toxic exhaust emissions harmful to health and this has been achieved through the imposition of increasingly stringent ‘Euro’ emissions standards. The ‘Euro 1’ standard (1992) heralded the fitting of catalytic converters to petrol cars to reduce carbon monoxide (CO) emissions while the latest standard, ‘Euro 6’, reduces some pollutants by 96% compared to the 1992 limits. The Euro 6 standard reduces diesel car NOx emissions by 67% compared with Euro 5 and, for the first time, established broadly similar exhaust emissions standards for both petrol and diesel.

Diesels needed an exhaust diesel particulate filter to meet the Euro 5 standard and will require additional exhaust after-treatment (NOx adsorber or Selective Catalytic Reduction) to meet Euro 6 standards. This is costly and complex and as a result we are starting to see the introduction of small, highly efficient lean burn petrol engines that are both turbo- and super-charged but that do not require all of the bolt-on exhaust filtering to trap and clean up their emissions.

Cars with a diesel particulate filter are really not suited to mainly town-based stop/start driving because the engine will not reach the normal operating temperature required for dpf regeneration.

Many cities across Europe are struggling to achieve legally binding air quality standards and have introduced or are planning to introduce Low (or Ultra Low) emission zones to try to address the issue. The London Mayor and Transport for London are currently consulting on proposals for a central London ULEZ from 2020 under which there would be an access charge for pre-Euro 4 petrol cars and pre-Euro 6 diesel cars.

On balance if you will be driving in urban areas or not doing extensive mileage then it would probably be best to opt for a petrol model or indeed hybrid or electric.

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