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Old 05-04-2021, 06:16 PM   #21 (permalink)
It's all about Diesel
 
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Originally Posted by Isaac Zachary View Post
This could not only increase efficiency, but also reduce major diesel pollutants such as NOx and particulate matter at the same time, and do so much more effectively than just spraying water into the intake.
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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Old 05-04-2021, 06:41 PM   #22 (permalink)
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Originally Posted by cRiPpLe_rOoStEr View Post
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.
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.
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Old 05-05-2021, 03:30 PM   #23 (permalink)
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alcohol / water

In Vietnam, we mixed methanol-alcohol and demineralized water together, for use in the Douglas A1 Skyraider, to protect the radial engine during high ordnance load takeoff. Once aloft, any remaining solution was jettisoned to conserve weight. I understood that this was it's sole purpose. Protection against destructive pre detonation.
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Old 05-05-2021, 08:22 PM   #24 (permalink)
It's all about Diesel
 
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Originally Posted by aerohead View Post
In Vietnam, we mixed methanol-alcohol and demineralized water together, for use in the Douglas A1 Skyraider, to protect the radial engine during high ordnance load takeoff. Once aloft, any remaining solution was jettisoned to conserve weight.
Interesting. I've been aware of the usage of WM-50 to prevent hot starts on gas turbines, while on piston-engined aircraft I've been more aware of its usage at high altitude.


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I understood that this was it's sole purpose. Protection against destructive pre detonation.
That's the most usual purpose on spark-ignited engines, as the water content allows a leaner AFR.

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