Give it a few years and there will be another outcry about dirty petrol engines. It's an easy way to separate people from their money. Successive governments have recognised the value of propaganda, especially when supported by carefully chosen bits of science whilst other bits are carefully omitted.
The NOx issue is a slightly hysterical one. NOx is present to higher levels in diesel engines because:-
1. they are un-throttled and run on 'excess' air, rather than on a strict 14.7:1 fuel:air ratio by mass. Air contains about 80% nitrogen and about 19% oxygen.
2. they run hot, this is what bonds the Nitrogen and Oxygen atoms together.
Now, hot running has a direct positive impact upon the reduction of partially burned fuel (carbon monoxide), unburned fuel (hydrocarbons) and soot particulates. Soot particulate emissions are largely addressed by the universal adoption of DPFs.
NOx is addressed by selective catalytic reduction systems that use the AdBlue branded additive. I notice the NOX protagonists don't bother mentioning SCR systems.
If we were to lower the combustion temperatures there will be a corresponding increase in CO, HC and particulate emissions. Along with an increase in fuel consumption.
As an interesting aside I am puzzled by the four figure sums charged to replace failed DPFs. My Peugoet 406 2.2 HDi was a 2001 year model. The first car ever to be fitted with a DPF. It was replaced at around 50,000 miles for under £200!!
