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Name: Heather S.
Status: other
Age: 20s
Location: N/A
Country: N/A
Date: 2000


Question:
How do oxygenates in gasoline help reduce NOx emissions? I understand that the presence of more oxygen makes combustion more complete, reducing CO and hydrocarbons. But how does increased oxygen lower the temperature of combustion for reduced NOx emissions?

I would like to know how the increased percentage of oxygen in gasoline reduces NOx. As I understand it, NOx are reduced when the air/fuel mixture in a combustion engine burns at a lower temperature. Adding oxygen to combustion makes the process more complete but does not necessarily lower the temperature. Doesn't it acutally increase the temperature?!


Replies:
Heather,

High compression engines require a superior grade fuel or antiknock compounds in the their formulation. In any case (as you correctly stated) the reactions occurring when such an engine operates with suitable fuel are producing high temperatures that encourage formation of NOx. Lowering the compression ratio also lowers combustion temperatures and thereby reduces NOx formation.

Oxygenates in the fuel simply allow poorer quality fuel to serve at lower combustion temperatures without producing destructive engine knock.

Because there is a limit to the amount of oxygen available in the air, and so little time for the fuel to burn as the engine runs, oxygenated fuel assists in more complete combustion by adding oxygen as part of the fuel itself. Thus, lower CO and hydrocarbon emissions.

Lower combustion temperature reduces NOx, oxygenates reduce CO and hydrocarbon emissions, and everyone seems to be happy. However, engine efficiency and fuel economy suffers. This makes no one happy.

Regards,
ProfHoff



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