Volumetric Humidity at given Temp and Pressure?

ssashton

1. The problem

I need some help in a car tuning project I'm doing, please!

I have a turbo charged engine and I have fitted water injection to cool the air charge entering the engine. The idea being that cooler air is more dense and allows more fuel to burn.

I need help to calculate the maximum amount of water that can be evaporated into the air charge before exceeding 100% saturation. Clearly if I inject more water than can evaporate it will displace air in the engine cylinder.


So in this case it is a 2,000cc engine, and without any water injection the intake air is at a pressure of 1.65Barg (relative to atmosphere) and a temperature of 130C. How much volume of water can be evaporated into the 2,000cc volume filled with air at these conditions?

3. The attempt at a solution
If I understand correctly then 100% relative humidity is the amount of water that can be evaporated in a set volume of air at a given temperature.

So I found a table showing that 100m³ of air at a temperature of 20^oC reaches 100% humidity with 1740cc of water.

So if we increase the air pressure by 1.65Bar, we should reach 100% humidity with (1740cc/1.65Bar) 1050cc of water.

An air volume correction factor for temperature can be applied. Every 10^oC increase in temperature increases the air volume by a factor of 1.04. However, volume is fixed here, so air density is decreased by the same. Air temp increases by 110^oC so (11 x 0.04 = 0.44) the water that can be evaporated should increase by 1.44. (1050cc x 1.44) 1510cc of water per 100m³ at 100% humidity.


100m³ = 100,000L
100,000L / 2 = 50,000
1510cc / 50,000 = 0.0302cc of water can be evaporated in a 2,000cc volume of air at 1.65Barg and 130C.

Is this correct?! What do you think?

References
Relative Humidity of Air at given Temp - http://www.engineeringtoolbox.com/st...air-d_260.html

Air Volume Correction Factor at given Temp - http://www.engineeringtoolbox.com/ai...ume-d_853.html