Adventures in Hypermiling - Increasing MPGs

[Butcher]

My take on that image: With the normal imperfect mixing of any engine, 12.6:1 makes sure there's enough petrol to burn all of the oxygen. When running 15.4:1 there is enough oxygen to make sure all of the fuel is burnt. Side note: I'm not disagreeing at all BTW. The typed word can often lead to misunderstandings.

Yes, I suspect with ideal mixing then stoichiometric would work out best, however it never is ideal so going a little leaner helps reduce rich pockets in the mixture.
Also 12.6:1 gives more power mainly because there is more fuel and sufficient oxygen to burn it and power is largely determined by the amount of fuel.

[badass]

Yes, I suspect with ideal mixing then stoichiometric would work out best, however it never is ideal so going a little leaner helps reduce rich pockets in the mixture.
Also 12.6:1 gives more power mainly because there is more fuel and sufficient oxygen to burn it and power is largely determined by the amount of fuel.

Also that even incomplete combustion can be "complete" e.g. CO as a waste gas rather than CO2 still can completely use up all of the fuel and oxygen - but the CO can be further "burned" with oxygen to release more energy (it produces a blue flame!)

[Butcher]

This is essentially what the catalyst does - burn off any CO and unburnt fuel. It's also why when you start some cars they are noticeably louder, the valve timing is altered on cold start to throw fuel down the exhaust to heat the catalyst.