Diesel Cars - Clean or Dirty ?

Diesel engines are found to be more economical & efficient than petrol ones. Even the petrol engines that offer direct injection are still less efficient than an average diesel run engine.

Although diesel and petrol fuel comes from the same oil (crude oil) – diesel boasts much more different properties than petrol. It is a known fact that diesel is more dense & contains around 15% more energy by volume. You can take that as 15 % more on every litre you use when driving – giving you more value for you money essentially..

Both engine types in the mechanical world are called ‘heat engines ‘ – which is due to the fact that the engine uses the energy gained from heat & high temperature (when burning the fuel) to convert it to mechanical energy that powers (or moves) the motor. Why do we mention this – well a diesel engine or rather the fuel itself is chemically better at doing just that – due to higher thermal efficiency – a diesel engine can more efficiently (about 40% more than petrol!) do the process of conversion from heat to mechanical energy – thus wasting less of the fuel (in comparison to petrol) and waste less of it in the air/environment. Actually, one of the reasons why CO2 emissions and road tax of newer diesel cars is lower than the same make petrol cars.

So why the bad press?

The controversial topic and question of vehicle emissions. Diesel produces less CO2 due to it being more efficient and burning less fuel. HOWEVER, it does create more NOx inside the combustion chamber (inside the engine) – although this has nothing to do with diesel itself – the NOx is a by-product of nitrogen (which is created only in high temperature combustion when burning fuel) combining with oxygen (NOx is created more when burning diesel fuel because of the previously discussed burn-efficiency characteristic that the petrol does not possess (as much)).

Because of this, diesels have an exhaust after-treatment in place such as SCR (selective catalyst reduction), and the latest diesels produce extremely low amounts of NOx. Although this explains how diesels are more economical and more fuel efficient (thus eco-friendlier) – where did the stigma around diesel engines come from?

Well it all comes back to corporate greed – (not to point fingers) but it all started around 2008 when Volkswagen ( or at least some of the Volkswagen top executives, as no one had a clue at the time) tried to play around with how the engine performed in laboratory tests and how it performed in real life… (The next chapter with the original link to source, can explain the situation in more depth) However, it was pre-programmed for the cars ECU (Engine Control Unit) to switch from almost-perfect fuel economy and high (NOx) emissions (when on road) to a not so good fuel-efficiency (still better than petrol though) and low (NOx) emissions when doing a laboratory test – apparently the vehicles ECU managed to understand when a car is being checked in a laboratory and switch between the two modes – which, when found out, created a massive chain of negative reactions from the press and the public and of course not only Volkswagen suffered, but also the good ol’Diesel engines name and trustworthiness suffered as well… The motivation? – We can only speculate, but a great guess would be – the manufacturer found a way how to stand out in MPG performance amongst its diesel competitors and well… just went for it – advertising and marketing becomes a lot more easier when your car is X times more efficient in fuel consumption and performs equally well in any other category…

‘’ Volkswagens were initially sold to the public in 2008. With the addition of a diesel particulate filter to capture soot, and on some vehicle models, a urea-based exhaust after treatment system, Volkswagen described the engines as being as clean as or cleaner than US and Californian requirements, while providing good performance. In reality, the system failed to combine good fuel economy with compliant NOx emissions, and Volkswagen chose around 2006 to program the Engine Control Unit to switch from good fuel economy and high NOx emissions to low-emission compliant mode when it detected an emissions test, particularly for the EA 189 engine. This caused the engine to emit NOx levels above limits in daily operation, but comply with US NOx standards when being tested, constituting a defeat device. In 2015 the news magazine Der Spiegel reported that at least 30 people at management level in Volkswagen knew about the deceit for years which Volkswagen denied in 2015. ‘’

All in all we hope that this helps to shed some light on diesels as a better fuel option (or at least equally good) to petrol fuel as well as to clear up the stigma around diesel engines! :)

If you have any more questions on diesel cars or annual DPF (diesel particulate filter) cleaning - just give us a ring or leave a inquiry on the Contact Us page! :)

- Your Premier Team