Re: DPF
@Steve, in the not too distant past, diesels were marketed as being a lot better in terms of grunt and power, because you could use heavier fuel oils. Petrol (or gasoline, in all y'all's parlance in the Leftpondian republic) requires lighter hydrocarbons which, if you have heavy crude oil, require some cracking (which adds to pollution). Light crude oil is easier to refine to petrol.
However, diesel comes with some drawbacks, as Mercedes and other diesel engine manufacturers discovered. Diesel you have to burn in one of two ways:
- You either have to burn diesel at a temperature that generates minimal nitric oxides (NOx), but that generates particulates of the PM10 and PM2.5 kind,
- Or you burn diesel at a high enough temperature that leaves no particulates, but you end up emitting a lot of NOx. Nitric oxides (i.e. NO, NO2, N2O, etc) are irritants and contribute to breathing difficulties.
Your general consumer diesel engine uses the first, because you can simply slap a DPF between the engine and the exhaust, which captures the sooty PM10 and PM2.5 particles, and leaves you with decent power and minimal NOx pollution. The engine doesn't have to burn at as high a temperature, which means it doesn't need an additive and a catalyser that deals with NOx.
For commercial/freight diesel engines, Mercedes, the inventor of AdBlue, suggested running the engines a lot hotter, but injecting a platinum catalyser with exactly measured urea compound (which is what AdBlue is) that will break down the nitric oxides into water, nitrogen and other, less irritating compounds. That takes care of having to clear/exchange the DPF often, but requires the additive instead.
I know AdBlue (and similar additives) have a bit of a bad reputation in the US, and the same with DPF (and I know a certain segment of society who actively modify their trucks to remove the DPF because 'I ain't lettin' some manufacturer tell me I can't have all the power I want from my truck').
The diesel engine scandal is related to this in that the manufacturers played with the Bosch injector controller to set it into a test mode that minimises the NOx output and passes emission tests, but then switches to a less... ahem, environmentally friendly mode once running at speeds that require more oomph. Cue a lot more NOx emissions from cars at 60+ mph (because the engine then burns hotter and gets rid of the particulates). Naughty manufacturers...