Originally Posted by Jono
...How does Exhaust Gas Recirculating assist with emissions? Anyone knowlegable care to explain..or have I got to try and research (Google can
be your friend)?
I am certainly not more knowledgeable with regards engines - but from a chemistry perspective, if I recall correctly, the aim of EGR is to reduce NOx emissions. Here is, from vague recollection, the chemical thinking:
- NOx's are formed at high temperatures, from mixtures containing nitrogen and oxygen (e.g. air!)
- higher proportions of oxygen cause engines to run "hotter"
- mixing exhaust gas with the incoming mixture reduces the amount of oxygen which makes it harder for NOx to form (as less "spare" oxygen) and runs cooler so less tendency to form anyway.
- the CO2 and H2O in the exhaust also help with "removal" of heat from the combustion chamber - as they have relatively high heat capacities (compared to air).
Now this was from some "fuel chemistry" lectures some years ago - my recollection was this being applied to Petrol combustion cycles - but I assume it is similar thinking on diesels.
Does that help?