Why Alcohol works better than water.

[Jon E]

I was reading through some SAE papers on water injection and found somthing that might explain why alky almost always works better than water for the intercooled TR.

From SAE paper 1999-01-0568:

Experimental test data show that water injection into an unheated manifold, when engine speed is reasonably high, will not give water a sufficent time to vaporise during the compression stroke. Of course, in normal operation of a naturally aspirated engine the water does not vaporise until after combustion is well under way. This effect explains why injection of water into very highly compressed or supercharged engines has been successful

This would explain why pure water works better for hot air motors and is less effective for intercooled engines.

When the water is injected into an air charge with a temp above 210* it "should" vaporise almost immediately (negating the impact of the added boost pressures effect on the boiling/vaporisation point of the water) thus removing a large ammount of heat from the air charge immediately, before it ever reaches the combustion chamber.

When the water is injected into a much cooler air charge (intercooled) it doesnt vaporise until the combustion process is underway and is less effective at removing heat. By the time the compression stroke has started it is too late for the water to have much of an effect at suppressing detonation. Which would explain why the supercooling of the alky is so much more effective at reducing ACT's for intercooled setups.

You guys might intrepret it a little differently than I did but I think this answers alot of questions, at least it did for me.

You can find the whole paper here:

http://not2fast.wryday.com/thermo/water_injection/1999-01-0568.pdf

 

[1badTTA]

That is a pretty good explanation and make alot of sense. Not going to hear any arguement from me on that one

 

[6SENSE]

Sounds like I need to add some water to my methanol...............whats an intercooler?

 

[turbo buicks]

that explanation also supports my theory of why liquids with a lower boiling point work better. methanol has a lower boiling point than denatured and works better at removing heat than denatured which proves my theory. maybe i should remove my i/c and run water injection, hahaha

 

[turbo buicks]

Originally posted by Jon E
explain why alky almost always works better than water

b/c its get your drunk faster

 

[b4black]

Originally posted by turbo buicks
that explanation also supports my theory of why liquids with a lower boiling point work better. methanol has a lower boiling point than denatured and works better at removing heat than denatured which proves my theory.

If it were that simple, then water would kick metanol's butt.

 

[turbo buicks]

uh ok, wtf. doesnt meth have a boiling point of 133 F? water is 212 F. im not following what ur saying, boj.

 

[b4black]

You're right, I'm wrong.

I got turned around backwards. In general, better heat removal would be accomplished by the liquid with the HIGHER boiling point. The higher boiling point equals a higher heat of vaporization. The higher the heat required, the more heat it absorbs. But in the example above, the water never gets a chance to vaporize correctly. The best would be the liquid that has the highest boiling point, yet still fully vaporizes. If ethanol is fully vaporized, it should perform best.