INSIGHT
Everything you always wanted to know about...
Diesel v Petrol
Rod Pesch, UKLA Technical Director
Diesel was once the automotive hero, offering better fuel economy and lower CO2
emissions
than petrol – can you explain the fall from grace? In the UK there are 38% fewer diesel car sales today than at the industry peak of 2011 when they made up 55.7% - across Europe a similar trend is visible with sales at a 17 year low, from a peak of 51% in 2015 to 36% currently, the lowest figure since 2001.
The current slump in new diesel car sales highlights a marked shift in the public’s perception of diesel cars and a dramatic loss of their appeal - this decline can be attributed to several factors. Government initiatives to lower CO2
emissions by promoting diesel cars has
changed; the focus has moved from improved fuel economy and lower CO2
emissions to greater concern
about local air quality and pollutants: NOx and other noxious particulates (PM10), are linked to lung disease, cancer, allergies and wider environmental damage.
Plus ever-tighter EU regulations for both petrol and diesel engines continue to challenge car manufacturers and adversely impact sales.
What are the EU regulations? Euro I, the first emissions standard was introduced in October 1994. Since then increasingly tighter controls have been imposed and the current standard, Euro VI, was introduced in 2014; new car models registered from this date must conform to rules which set the mass and nature of pollutants emitted from a car’s exhaust over one kilometre, a measure by which new car approval is granted.
14 LUBE MAGAZINE NO.153 OCTOBER 2019
How are diesel car manufacturers responding to the challenge?
Significant advances in diesel vehicle technology have seen the introduction of special exhaust filters for particulates (DPFs) and Selective Catalytic Reduction (SCR) for the NOx. The filters are subjected to ongoing in-service regeneration and the catalyst works in conjunction with a special Urea and deionised water solution (AdBlue) which is sprayed into a diesel engine’s exhaust system, significantly reducing the amount of NOx emissions before they leave the exhaust. There is an alternative system, Exhaust Gas Recirculation (EGR) which involves recirculating a portion of exhaust gases with air which lowers combustion temperature. Passenger car diesels with either SCR or EGR since 2015 meet the London Ultra Low Emission Zone (ULEZ) emission limits.
Does AdBlue technology apply to both Heavy Duty and Passenger Diesel engines? Yes, AdBlue is used in both commercial and heavy duty diesel as well as passenger car engines. Europe is the largest SCR and AdBlue market in the world. It is forecast to grow rapidly at an average rate of 18% year on year over the next 10 years with the enforcement of increasingly stringent emissions standards. Given new Euro VII rules are imminent but as yet unknown, both diesel and petrol engines
continue to face challenges – petrol because CO2 emissions must fall to 98g/km by 2020. And diesel because more stringent particulates regulations are expected.
Are the rules for both petrol and diesel engines the same under Euro VI? No, the rules for petrol and diesel-engine cars are different. Modern diesel engines are cleaner and less polluting than their older counterparts, emitting around 20 times less harmful emissions today than ever before. Under Euro VI levels of NOx are lower than previously – diesels 0.08g/km max and petrol 0.06g/km max.
Euro V rules still allowed for petrol cars to emit more carbon monoxide and hydrocarbons than diesels, while diesels could emit more nitrogen oxide. However, the new Euro VI rules which came into force fully in September 2015, now require diesel car engines to produce far less NOx (nitrogen oxides) and THC + NOx (combined hydrocarbons and nitrogen oxides) than previously allowed under Euro V rules.
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