With climate change at the fore of many people’s mind’s, and cars being one of the biggest contributing factors to climate change in an average family, diesel is now being touted as one of the more fuel-efficient choices one can make. Diesel engines can take about 20% less fuel than a comparable petrol engine, and are increasingly being found in smaller cars. Added to much smarter engine designs, diesels are gaining popularity. However, two things concern me about diesel powered vehicles, and both of those concerns are tied to what comes out of the arse-end of the car.
As Trevardy put it, even with the new engines, diesel cars will often still leave a plume of black smoke when taking off at the lights. This got me thinking, for the 20% less fuel you use, do you actually put out 20% less greenhouse gases? If you look at the european emission standards, we can see that diesel cars indeed have different standards to petrol cars, and in some cases the levels for diesel engines is greater than that for petrol engines.
However, we can see that if we simply take a sum of both greenhouse gases (Carbon Monoxide + the Nitrous Oxides) we get more of them in petrol cars (around 20% more, interestingly enough. Petrol, I guess, predominantly emits CO and Diesel the NOxes). So, if CO is as bad as, or worse than the equivalent weight of NOx, Diesel cars on Euro IV emission standards are actually better than the equivalent Petrol cars. However, if the NOxes are about 1 and a quarter times worse than CO, then the petrol cars are about even (or better than) an equivalent Euro IV Diesel. I guess it’s probably a wash from my analysis, just make sure whichever car you get is Euro IV compliant.
Secondly, in a recent episode of catalyst exploring micro particles that a school in the inner city is exposed to, the conclusion ran along the lines of “the levels for micro particles are below what the maximum recommended levels are, with the exception of spikes when a truck drove by.” That is to say, the exhaust fumes for a (large, truck-based) diesel engine generated far more micro particles (which cause many serious health issues) than the predominantly petrol engines on our roads.
Note that the Euro IV standards mention particle matter, which is the micro particles I’m talking about here. I would say that petrol probably doesn’t emit much PM, since there’s no amount written under Euro IV, however, under the proposed Euro V standards, it shows petrol as having a maximum amount of PM. Whether that’s for consistency with Diesel or whether petrol does actually put some PM out there, I’m unsure. Having said that, I’m fairly certain that Petrol engines must not put very much particle matter into the air, and that limiting the amount of PM for diesel implies that the designers of diesel engines need to be careful about PM. However, I guess 0.025 g / km is reasonable.
In conclusion, when getting a new car, make sure it meets Euro IV emission standards. Taking less fuel doesn’t really mean much otherwise.