"Tim+" wrote in message
...
NY wrote:

I'm not sure what is is about compression-ignition that produces higher
NOx
than spark ignition.

Im pretty sure its just down to cylinder pressure and consequent
combustion temperature.

Nitrogen is pretty inert but the hotter you heat it the more NOx you get,
petrol or diesel. Diesels just have a bit of a head start on the
combustion pressure/temperature.

Ah, for some reason I'd always thought that diesel engines ran a lot cooler
than petrol engines. Higher pressure but lower combustion temperature.
Evidently not.