I am trying to understand what the limits are of pre-compressor methanol injection on turbocharged cars.

From my understanding, erosion occurs when you have the wrong combination of compressor speed and droplet size.

I have a turbocharger and I calculated the tip speed of the compressor to be at about 1158 ft/s at maximum boost.

My question is if the inlet tubing to the compressor is 3 feet long and I am flowing 100 ml/min of pure methanol (tiny amounts) will I see erosion if my ambient inlet temps are 80 degrees F?

I did a quick hand calc and the speed the air is moving through the inlet tube is about 160 ft/s so it will take about 20 ms for the air to reach the compressor.

I dont know how to compute the content of liquid left in this mixture, the methanol is injected via a super atomizing nozzle. So inlet droplet size can be assumed some value. I just dont know droplet size at the end of the tube feeding the compressor.

Why would you want to inject at pre-compressor stage? The higher the temperature difference, the more efficient cooling will be. I can see a case where you'd argue to inject before any intercooler, to use that gain, but not before the compressor.

In general, methanol is injected either directly into the cylinders or into the inlet ports of the engine, when used as "regular" fuel. This does prevent most effects of long term corrosion. When risking the chance of condensation of your methanol onto the compressor wheel, intercooler and inlet tract, you will probably expose your aluminium much more than when injecting further towards the inlet valves.

I don't think that experimenting with the size and concentration of the droplets will make a fundamental difference. Maybe a practical, but you're still exposing aluminium to (heated) methanol. It will corrode in the end. I don't know if cavitation plays a part in this process, but purely chemical, concentration and temperature are your main factors. If cavitation plays a part, you'd want the stuff evaporated before it hits your compressor wheel. If not, you'd want large droplets so only a small portion of the alcohol is directly exposed to the aluminium and most will just fly past and evaporate further down. Maybe the high impact speed at the tips of your compressor wheel would cause cavitation in larger droplets?

Remember that the evaporation of the methanol is what cools the mixture, once it's gaseous, it's just another gas that you are heating. It makes sense to evaporate it at the point where temperatures are highest. That would be either just before the intercooler, or during the compression stroke inside the cylinder.

Methanol has a high latent heat value, so it would provide a nice reduction in charge air temps.

The droplet size would not likely be an issue, since the small amounts of methanol you propose to use would readily vaporize before contacting the compressor wheel.  But methanol is also very corrosive to some metals/materials/ball valve.  So you would need to check for compatibility.

You would also need to make sure that your turbo's compressor shaft seals are capable of keeping the methanol out of your lube oil.