Quote:
Originally Posted by mnmarcus
My next question would be why aren't all cars lean burn? I assume lean burn turns on and off or is adjusted by the engine control unit? I'd also assume there are times lean burn is not more efficient mpg wise, right?
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Why not? Lean burn gasoline systems do not do well with catalytic converter systems that consumers are willing to accept. Your modern catalytic converter system requires an exhaust input that has some little bit of unburned hydrocarbons, some little bit of oxides of nitrogen, and some little bit of carbon monoxide (just not all at once). This is why gasoline cars generally burn near stoich at idle and crusing loads. Lean burn causes carbon monoxide emissions to generally go down, at the expense of higher oxides of nitrogen and unburned hydrocarbon emissions.
You can redesign a catalytic converter system to work with lean burn, but it'd add a lot of cost to the price of a car.