Originally Posted by Braineack (Post 144008)

I'm trying to picture Robert walking into Sally's Beauty Supply...

Originally Posted by jwarriner (Post 146155)

I've mixed both acetone and xylene in my gas tank with similar results. It works ok. I don't know if I'd directly inject either one.

Originally Posted by jwarriner (Post 146623)

It raises the octane of your fuel but I don't think either one will have the intercooling effect of methanol, and especially not water, which is the point of water/alcohol injection. The latent heat of evaporation of acetone is about half of what methanol is and benzole, which is very similar to xylene, is about 35% of meth. And for what it's worth, I personally wouldn't waste my time with water either, I'd run straight methanol maybe with an additive like Top Lube or Upper Lube.

Originally Posted by LS1 Bound

I want to address the issue of knock and what causes it.

Consider the following liquids and their heats of vaporizations.

Water 40.655 KJ / mole or about 2259 KJ/Kg water
Methanol 35.2 KJ /Mole or about 1102 KJ/Kg Methanol
Pentane 25.77 KJ/mole or about 357 KJ/Kg Pentane
Octane 38.8 KJ/mole or about 339 KJ/Kg Gasoline.

As you can see, the cooling effect of Methanol is significantly higher than the cooling effect of Octane. Different fuels have different heats of evaporization. Look at water however. For cooling - no contest.

Knock is more complex than this however. Temperature certainly plays a role, but it is not the only parameter that plays a role.

Knock is caused by the rate of reaction (more specifically, the speed of the flame front) exceeding the speed of sound.

As temperature goes up. Molecules move faster. If they move fast enough you may knock (faster flame front). You can reduce the velocity of the molecules by cooling them. In fact, temperature is really just a measure of the mollecular velocity. Cold air has slower moving molecules. If a fuel molecule is moving faster, it will find an oxygen molecule faster.

Adding methanol molecules to compete with gasoline (octane molecules) will certainly reduced knock. Methanol is a slower burning fuel. Why???

Methanol works not by lowering the temperature, but by reducing the rate of reaction statistically.

If we look at a specific volume of methane, it will contain more molecules (lower atomic mass) than a high atomic mass fuel like Octane. This means that during the combustion reaction, a Methane molecule is more likely to hit a nother methane molecule than it is likely to hit an oxygen molecule. If it hits another methane or an Octane molecule, it does NOTHING. It bounces and maybe it hits an oxygen next time, maybe it hits a Nitrogen or another methane, or an octane or one of the products of combustion, water and CO2.

In any case, the more methanol you add, the slower the reaction proceeds because of statistics/kinetics.

It takes longer to burn and will produce lower pressures and will thus yield lower power. Even though the reaction will proceed to completion. The torque developed during the power stroke will be reduced.

The idea is NOT just to burn as much fuel as possible! It is to make the most power with the least amount of fuel and to get the maximum torque from your power stroke.

Using high mollecular weight fuels decreases the number of fuel molecules per mass. This means that there are fewer fuel molecules "searching" for oxygen molecules before some sort of reaction takes place. The reaction is quite complex and will produce many intermediate products until all fuel product has been oxidized. Having said this, we start out with a faster reaction because there are fewer fuel molecules (although they are large) - before the spark provides sufficient activation energy to start the reaction. There are plenty of oxygen molecules and very few few molecules.

Since there are many more molecules of Methane per specific mass, there is a greater chance of a fuel molecule hitting another fuel molecule and doing nothing instead of adding to the rate of reaction.

Now you have to ask yourself what you are after. Are you trying to get maximum power from a low energy fuel or decrease the power of your high energy fuel. Pick one and go with it. In the end, if you do both, you lower efficiency and maximum yield.

Higher Temperatures, produce the highest pressures. Faster flame fronts give the maximum efficiency. As long as the flame front does not exceed the speed of sound (in a combustion chamber) you will get the best power. If they exceed the speed of sound, you will make the most power, but it is unlikely that a gasoline engine will survive for long.

Those adding Methanol are lowering the rate of reaction statiscally. Those adding water are lower the rate of reaction Thermodynamically. There is a cost to using Methanol. There is none in not. The results are same. The efficiency is what changes. Adding methanol is expensive and yields the same thing. Add water to bring the temperature down to where there is a comfortable safety margin and stop there.

Sam

Originally Posted by J_Man

Here is a paper directly from NASA, from their Aircraft Engine Research Lab. It shows comparison between just water and water/methyl alcohol, etc. mixes for water injection:

http://naca.larc.nasa.gov/reports/19...report-812.pdf

Their summary:

1. In all cases the use of methyl alcohol-water, monomethylamine-water, and dimethylamine-water mixtures as internal coolants raised the knock-limited performance of AN-F-28 fuel more than did water alone.

2. The addition of ammonia to the methyl alcohol-water solution as an internal coolant lowered the knock-inhibiting effects of the solution and also promoted surface ignition.

3. The commercial trimethylamine-water solution lowered the knock-limited performance of the AN-F-28 fuel except in the very rich mixture region

4. At fuel ratios of 0.05 or less, extremly high knock-limited powers could be obtained by using internal coolants.

5. At fuel-ratios lower than the stoichiometric-mixture ratio, addition of each of the internal coolants except water lowered the indicated specific fuel consumption, in some cases to an amount greater than can be explained by considering the contributions of the internal coolant to the heat of combustion.

6. Internal cooling at extremly low fuel-air ratios allowed high knock-limited powers at much lower indicated specific liquid consumptions than were obtained when operating at high fuel-air ratios either with or without internal cooling. (Lean mixture operation, of course, implies high indicated specific air consumptions)

7. The use of monomethylamine-water mixture at an inlet-air temperature of 150F and a fuel ratio of 0.049 allowed a knock limited power of 1.96 horsepower per cubic inch of cylinder displacement (imep of 620 lbs/sq in). The corresponding indicated specific fuel and liquid consumptions wer 0.37 and 0.55 pound per horsepower-hour, respectively.