By friendzis
[I am not an expert, but] first there are controllable emission control devices (e.g. EGR) and secondly burning conditions (thermodynamic cycle) highly influence power and emissions (emission mixture), i.e. how much power and emissions you get from burning 1 g of fuel.
An intuitive analogy: when you are camping (or just use firewood in a grill) and are just starting a fire there is a lot of smoke, although the fire is relatively small. When you get it hot and burning nicely there is barely any smoke left, although you burn much more fuel per time.
For an internal combustion engine the factors determining power/emissions are mainly fuel/air mix, ignition angle (gasoline), fuel injection pattern (for direct injection engines – all “modern” diesels, VW [T]FSI gasoline) and or air/mix injection angle (variable camshaft timing).
Fun fact: modern diesel cars have a DPF designed to limit emissions (fumes mainly). Engines have special DPF cleaning mode designed to kick in in highway modes by slightly increasing exhaust gas temperature. Driving only in urban cycles causes a DPF to get clogged, engine enters deep cleaning mode from time to time (power loss, dark fumes out of “chimney”) which has a negative net effect on particle emissions, which are arguably most detrimental to respiratory tract.
link
See more about this article by clicking the link here: https://news.ycombinator.com/item?id=10256933
friendzis comments on "Researchers Could Have Uncovered Volkswagen’s Emissions Cheat If Not for DMCA"