If I poke a couple of fingers up my (Euro-6) Mazda’s tailpipe and wiggle them around (donít worry, itís not habit-forming) they emerge unsullied; do the same trick with a similarly-modern petrol vehicle, and I get sooty fingers! Do you think this says anything more general about relative levels of carbon particulate emissions in the diesel versus petrol debate?
I well recall another reader saying that he had just done what you did on his new Mercedes-Benz (with DPF) quite some years back and reported much the same as you ñ a clean finger! As you suggest, it begs the question about how clean many petrol cars really are. To be fair, many of the latest (direct injection) petrol engines now have GPFs fitted (Gasoline Particulate Filters) in order to meet the latest particulate emissions regulations ñ specifically in this case now for the “Particulate Count.” This addresses the issue of particulates so fine that their mass is almost impossible to measure accurately, as they are invisible, so they are measured by number. Their numbers are positively huge ñ the regulatory limit being 6 x 10 to 11th power, (six hundred billion, in words) particles per kilometre, and some 0.0045gm/km by weight, in the new WLTC test.
Enough of such silly figures. You and I both know that you can still see petrol and diesel cars belching out black smoke that must amount to many powers of ten times the regulatory limits, and until they start doing roadside testing, maybe with an immediate seizure of vehicles exceeding the regulatory limits by a certain (no doubt arbitrary) factor, then I feel little will change in real life with lots of older pre-Euro 5 vehicles still on the road. I think it’s probably fair to say though that petrol engine smoke comes primarily from cold engines, and this issue seems to have been cunningly by-passed (because to do otherwise would rock the regulatory boat, and probably capsize it!) with the high temperatures used in official regulatory testing, thus minimising cold engine effects. It leads me to a personal obsession on the disregarded benefits of fitting plug-in electric heaters for engine pre-heating, to vastly reduce those cold engine emissions. Such simple technology, with a maximum cost, maybe, of £50 a car, fitted during manufacture and easily fitted in the same locations in the same engines as the plug-in ìblock heatersî widely used in Norway, Finland, Canada, etc. An easily engineered piece of what you could hardly even call ìtechnology.î
You PMs of a DPF equipped diesel are so small you cannot see them, when the car is performing an in-drive DPF regen, the car produces approx 5 to 6 mg/km of particulates, other than a DPF regen the pms are below 0.01 mg / km