On 27/05/2022 13:59, Tim Lamb wrote:
>
> I thought the system only altered the injected fuel quantity.
>
> Seems a lot. Does this mean the only diesels meeting the emission level
> use ad blue?
I don't know exactly what they did but generally you need heat, pressure
and air to create NOx. At low injection levels because the diesel takes
in much more air than the fuel needs to burn the temperatures are low
so not much NOx forms. At full power the temperature goes up as does the
pressure but there is far less excess air as the fuel uses most of it
up, so not much NOx forms. The problem occurs when there is just enough
fuel injected to raise the temperature and pressure to sufficient levels
but there is plenty of excess air present so NOx becomes a problem.
So yes the only control available is how and when you inject fuel.
On a test you can probably avoid this high NOx part of the operating
cycle but the power curve would make normal driving difficult.
Adblue is injected into the exhaust to react the NOx back to Nitrogen
and steam in a catalytic converter so its use is linked to this part of
the fuel-rpm map.
What I cannot understand is why modern diesels with particulate filters
and adblue are still being vilified when their levels of pollutants are
an order of magnitude lower than a 2010 diesel without those, I still
drive a non DPF non Adblue diesel from that era, though only did 1500
miles per year for the past three years.