Quote:
Originally Posted by cRiPpLe_rOoStEr
NOx and PM emissions decrease exactly because the water injection is done into the intake. Injecting it along the fuel won't either cool the charge air which leads to lower NOx, or decrease heat irradiation through the engine coolant (thus retaining a higher amount of energy during the compression stroke to be converted into motion at the power stroke). Such heat conservation also increases the speed of the flame spread, thus leading to a more accurate combustion decreasing the PM emissions.
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All I know is that according to the papers I've read, emulsified water injection reduces NOx and PM emissions better than intake spraying does.
NOx is reduced because the overall combustion in a diesel is already very cool and only produces NOx at the rich point where the injection is occuring. Lowering the whole cylinder temperature through intake injection won't help lower NOx as much as putting the water where the NOx would normally be reduced.
I don't see how heat conservation increases flame spread if the injection is local and rich. Water droplets there push the flame and fuel out into the "fresh air" of the combustion chamber.