Water vs Methanol : Ultimate Tuning

[parmas]

Yet another question came to my mind....

Let's make it simple. Imagine 1degC cooler air has an extra particle of air.

So if we have an ambient temperature of 40degC meaning 40air is being used from the ambient every charge and cooled the charge to 10degC by any means.

From where the extra 30air came from?

[rotrex]

That "extra" air is provided by your turbo or supercharger. All you do is changing its flow and pressure ratio. As long as your boost is regulated, you will maintain the pressure, but get extra air though a increase in air density. In case of a unregulated supercharger like in my set-up, boost actually drops as you cool more. What makes the power is the charge density. It is determined by both pressure and temperature.

[parmas]

Originally Posted by rotrex

That "extra" air is provided by your turbo or supercharger. All you do is changing its flow and pressure ratio.
As long as your boost is regulated, you will maintain the pressure, but get extra air though a increase in air density.

More boost is always equal to more power at any given air temperature until detonation or pre-ignition occur.


In case of a unregulated supercharger like in my set-up, boost actually drops as you cool more. What makes the power is the charge density. It is determined by both pressure and temperature.

What I am saying is that if keeping a constant boost pressure eg:20psi with a constant ambient temp of 40DegC, injecting post turbo will eventually cool the incoming charge to 20C.

Will the 20DegC difference create more air going into the cylinder or just cool it?

What about oxygen in this case, the primary subject. Will it increase or decrease?

[rotrex]

Mass air flow will increase and hence total oxygen.
Someone once did the numbers (enthalphy of evaporation, head capacity of air, vapor density of methanol etc.) and found that for every 1% of methanol (1% of total air flow), mass air flow increases by 2%.
Now evaporating an extra of 4 gram/sec (5 ml/sec or 300ml/min) of methanol wil increase air mass flow by 8 gram/second which would result in an other 10HP from the extra air alone.
Let's try an approximation outselfs:
Methanol has roughly 1.15 kJ/g heat of evaporation and a vapor density of 1.1 g/l. Let's say 1 kJ/g. Makes life easier. The vapor density is very similar to air. The heat capacity of air is roughly 1 kJ/kgK. So evaporating 4 g of methanol per second (300ml/min) consumes about 4kJ of heat per second (4kW). That 4kJ can cool 250g (good for 300HP) of air down by 16K. At the same time it releases 4 g of vapor. The 16 K temperature drop increases air density by about 4%. The vapor replaces about 4/250g or 1.6% of the air. So you gain 4% and lose about 2%. :-)

Water has twice ther heat of evaporation. But it evaporates very slowly compared to methanol. It therefore contributes much less to intake air cooling unless things are very hot.
At 20PSI air is very hot after the turbocharger. Say 150C. Here the water contributes a lot to cooling. Once things get below the boiling point, evaporation speeds drops a lot.

[Flr Power]

I don't think water has to be in a vaporized state to do it's job because it will vaporize once the combustion process starts.

[parmas]

Originally Posted by rotrex

Mass air flow will increase and hence total oxygen.
Someone once did the numbers (enthalphy of evaporation, head capacity of air, vapor density of methanol etc.) and found that for every 1% of methanol (1% of total air flow), mass air flow increases by 2%.
Now evaporating an extra of 4 gram/sec (5 ml/sec or 300ml/min) of methanol wil increase air mass flow by 8 gram/second which would result in an other 10HP from the extra air alone.
Let's try an approximation outselfs:
Methanol has roughly 1.15 kJ/g heat of evaporation and a vapor density of 1.1 g/l. Let's say 1 kJ/g. Makes life easier. The vapor density is very similar to air. The heat capacity of air is roughly 1 kJ/kgK. So evaporating 4 g of methanol per second (300ml/min) consumes about 4kJ of heat per second (4kW). That 4kJ can cool 250g (good for 300HP) of air down by 16K. At the same time it releases 4 g of vapor. The 16 K temperature drop increases air density by about 4%. The vapor replaces about 4/250g or 1.6% of the air. So you gain 4% and lose about 2%. :-)

Water has twice ther heat of evaporation. But it evaporates very slowly compared to methanol. It therefore contributes much less to intake air cooling unless things are very hot.
At 20PSI air is very hot after the turbocharger. Say 150C. Here the water contributes a lot to cooling. Once things get below the boiling point, evaporation speeds drops a lot.

The theory of methanol is good since meth itself is an oxygenated fuel.
Although water does not create oxygen while evaporation but more works as a potent air charge coolant vs meth.

Here comes the thing, water as the best air charge coolant dissipates more air than meth through evaporation.

So would't the theory of denser air work here?

[rotrex]

Neither methanol nor Water creates any Oxygen while burning.
My calculations from above are only talking evaporation into account. You were asking about if evaporation of methanol in the inlet increases air and with it oxygen density.
Answer is yes, it does.
Water is much similar except for two things. It's heat of evaporation is twice as large while its vapor density is lower due to the lower molecular weight of water vs methanol.
But let's assume vapor density is the same to keep things easy.
You could conclude water cools twice as much as methanol. That is the theory if all the water would evaporate. In your 40C airstream, it does not. That is the thing. The water's vapor pressure is MUCH higher than the vapor pressure of methanol. Water evaporates MUCH slower than methanol. Cooling power is joules of heat of evaporation per second.
Before digging out any equations a first approximation would be 10x slower. This is very crude since these are highly nonlinear phenomena that happen on a logarithmic scale. Once you hit a boiling point, things change again.

Just put some water over your finger and methanol. What feels cooler?

If you have a very hot environment such as a gas turbine with its 40:1 pressure ratio and 1000C air exiting the compressor, water injection works as theoretically predicted as all water evaporates. In a inlet tracks with 150C 20PSI air exiting the compressor and cooling down to 40C things are more complicated. Here rather less water will evaporate, some of the water evaporated in the compressor will even condensate again. Here methanol will do the majority of the cooling work, not the water.

In the cylinder things will get better as things get hotter, but still big droplets won't even fully evaporate during a entire combustion cycle.

Now water is not best, it is just different. In the cylinder it slows down flame propagation speed. Now if the distribution is not perfect within the cylinder, you still experience knock from the perimeter zones of the cylinder that contain less water.

Water and methanol work well to gether. They work on different temperature and time scales and act differently,

Here are some experimental data on the evaporation speed of a few solvents. Under the same conditions in this rotary evaporator, Methanol evaporates 8x as fast as water.
http://data.biotage.co.jp/products/t...ation_rate.pdf

The evaporation time of a droplet is about proportional to its diameter. A 200µm droplet takes 4x the time to evaporate than a 50µm droplet.
Air assisted nozzles create a finer mist than hydraulically driven nozzles. if the water mist is fine enough, it will also evaporate reasonably fast, at least until the air is saturated. But in the cylinder, the very fine residual water mist will help equilibrate in cylinder temperatures. it will also slow down flame development speed. This is where the extra timing requirement comes from. Methanol on the other hand burns faster than gasoline. a mix of methanol and water requires less extra timing. it is therefore easier to tune and can extract more power than water alone is most instances at the same boost level. You might achieve more power with water alone, but you need to add more boost. And there are limits in most setups.

In WW2 this was well optimised. water is the main agent, but methanol water mixes made more power with less tuning over a wieder AFR range.
As all planes except the FW190, it had a single throttle control lever, had manual fuel control. You had to adjust throttle, ignition timing and AFR yourself while manually open and close oil cooler covers and other stuff. When now folks start shooting at you, you did not want to fine-tune everything and watch EGR gauges while engaging war emergency power = water methanol injection. It only required little adjustments.

Pure methanol would require more adjustments and more of the stuff= weight = less time on big power = potential death.

also remember that those engines were running at very high pressure ratios. A P-47 Thunderbolt would run with up to 1.7 bar of manifold pressure at 30000 feet. Atmospheric pressure at this altitude is 0.3 bar. This corresponds to a pressure ratio of almost 6!!!!! At 0°C and a 75% efficiency you end up at turbo exit temperatures of 250°C. Pre-turbo water methanol injection had a huge effect. The water would literally boil while the air was compressed.
Richard L wrote that the WRC engines were driving the turbos at pressure ratios of 4 due to he inlet restrictors. This makes then very inefficient leading to very hot air temperatures. They used water injection to great effect. Water methanol would have even been better for power, but was not allowed.

[parmas]

Very good. Thanks rotrex for the detailed explanation.

In my case running intercooless setup, what mixture would you recommend to be ideal?

Would mixtures post/pre turbo be the same or there is a potential mixture for pre-turbo that works best?

[rotrex]

From what I can make up now, there are different scenarios:
1. Ditch pre compressor jets and inject post CC or direct port with the mix that gets you the best power. While 50:50 has its merits, I have now seen that for a given mix flow and boost more alcohol can in my car make more power. The other possibility would be to inject even more 50:50 mix.
2. Install a air assisted nozzle upstream of the turbo as in Riceracing's system. A significant portion of it's very fine mist will pass the CC. The evaporation in the turbocharger reduces droplet size even further with the majority of the vapor being the more volatile methanol. This leaves the water to do the cylinder work. As the mist is very fine, little fluid will separate in the CC. Even if, it does no harm.
3. For maximum charge cooling, inject 80:20 methanol water into the compressor. Supplement as needed post charge cooler or direct port. The more you inject, the less the CC will do.
4. If your CC is on the small side of things as in riceracing's system, pre compressor helps to lower overall charge temperatures. The too small CC itself cannot bring down air temperatures as logos as a bigger one. If you can install a big air to air cooler at the front, you will get air temps 10 to 20c above ambient. There pre compressor injection will lead to little extra cooling. Part of the evaporated mix will condensate. Here post CC injection or direct port will be more efficient. Exception would be a undersized turbocharger with a low efficiency.

Don't make the system too complicated, e.g. Two separate fluids and injection systems.
You can get to the same result by plainly injecting more of whatever fluid you use. This is more simple, easier to tune and less prone to failure.

Just my thoughts.

[parmas]

Originally Posted by rotrex

From what I can make up now, there are different scenarios:
1. Ditch pre compressor jets and inject post CC or direct port with the mix that gets you the best power. While 50:50 has its merits, I have now seen that for a given mix flow and boost more alcohol can in my car make more power. The other possibility would be to inject even more 50:50 mix.

Swapping the pre compressor jet with direct port will net increase in air temperatures while more methanol is available for burning. Less methanol is lost.
Swapping pre-compressor to another 2nd post jet will not yield any benefits as I am already above 100% Relative humidity.

2. Install a air assisted nozzle upstream of the turbo as in Riceracing's system. A significant portion of it's very fine mist will pass the CC. The evaporation in the turbocharger reduces droplet size even further with the majority of the vapor being the more volatile methanol. This leaves the water to do the cylinder work. As the mist is very fine, little fluid will separate in the CC. Even if, it does no harm.

Will consider this... any links for more info/video/pics ?

3. For maximum charge cooling, inject 80:20 methanol water into the compressor. Supplement as needed post charge cooler or direct port. The more you inject, the less the CC will do.

Would not 80% meth oxidize the compressor wheel? Why 20/80 W/M ?

4. If your CC is on the small side of things as in riceracing's system, pre compressor helps to lower overall charge temperatures. The too small CC itself cannot bring down air temperatures as logos as a bigger one. If you can install a big air to air cooler at the front, you will get air temps 10 to 20c above ambient. There pre compressor injection will lead to little extra cooling. Part of the evaporated mix will condensate. Here post CC injection or direct port will be more efficient. Exception would be a undersized turbocharger with a low efficiency.

With the low compression and target bhp the turbo was small that's why I pre-turbo injected to increase efficiency. Now I am upgrading to high compression engine and have the turbo efficiency back in line. Pre-turbo could not be needed anymore

Don't make the system too complicated, e.g. Two separate fluids and injection systems.
You can get to the same result by plainly injecting more of whatever fluid you use. This is more simple, easier to tune and less prone to failure.

AGREED. The only issue I have is that I need to wire the water injection directly to the ecu.

Just my thoughts.

Cheers Rotrex