New Beta Alp 4

[catcitrus]

In a sensible world it would be, but a lean engine produces NOx. So, its all about having a furnace-like cat to burn the hydrocarbons etc down.

NOxis a high temperature combustion product so I don't agree with your comment. With a 3 way catalyst then the deNOx bit only works when there is no spare oxygen in the exhaust--hence the lamda sensor in the exhaust to control the air/fuel ratio. Lean burn a couple of points above stoichiometric is the most economic, but enabling a NOx catalyst to work requires a richer mixture. Early catalysts were simply hydrocarbon burners.

[Richard Simpson Mark II]

But a lean burn also means there is excessive oxygen, which will combine with nitrogen to form NOx if it can't find any hydrogen or carbon.

In the combustion process there are always small pockets where temperatures are high enough to form NOx.

NOx is the pantomime villain of air pollution in the London ULEZ...ironically it is formed in the human nose where it "plays several roles in the maintenance of physiological homeostasis and the regulation of airway inflammation"
So, it's actually good for human health.

[garyboy]

see !!! .... I always knew bike fumes waz good for you

[Richard Simpson Mark II]

Legendary Norton tuner Joe Craig always knew when he had the fuel on an engine 'spot on' because of the sweet smell of NOx in the dyno room.