Diesel cars have significantly lower carbon emissions than petrol cars and even than some electric car usage when accounting for the energy production. Diesels are even the best placed to run on biofuels.
Why single them out?
Why single them out?
Unlike a catalytic converter though, eventually (after 150,000km or so) they will become blocked up and cause a noticeable drop in power or cause engine fault codes. At that point you need to replace it, which could be a few thousand Euro for a new DPF, or the more common option is to remove it. This is illegal in most EU countries, but also a blind eye is turned to it - even in places with strict emissions checks like the UK.
AdBlue is a modern way of reducing this even more, but there are already devices you can buy that will trick the ECU into thinking your tank of AdBlue is full when its actually empty.
Combined with other common issues like injectors wearing out, as a diesel engine gets old it will burn fuel a lot dirtier than a similar aged petrol engine.
However any mass adoption to biofuels would require different engine (existing engines will work fine on a low blend of biofuels, but very few will work on 10P%). For cars, why would you stick with a biodiesel engine which is more complicated and has higher levels of other pollutants, than some sort of biogasoline engine?
Hemp oil powering diesels is possibly the most efficient locomotion path we have, only really competing with electricity generated with little carbon emissions.