Quote:
Originally Posted by rotrex
Having done some experiments with pre compressor injection last summer and fall, I can add a little to this.
Rotrex C30-94, jets tried: Aquamist 0.3 and 0.5mm. Mix 50:50 water methanol by weight.
IAT is measured after a water cooled charge cooler half way before entering the intake plenum. Throttle body is before the SC. Boost is 0.83 bar at 7000 rpm.
There is almost no influence on boost. At least nothing I can distinguish from effects of ambient temperatures. So all constant within a few percent.
The air temperatures drop as you increase jet size. Going from 0.3 to 0.5 mm introduced IAT fluctuation that got worse as ambient temps were lower. The sudden nature of those drops, you can see this effect also in the original data plots of this threat, can in my opinion be attributed to condensation in the charge cooler. The big droplets hits the IAT sensor, it has a little frame around it, evaporate and cool it down. Once the droplet is gone, it heat up to the air temp again. The fluctuations go worse as ambient temperatures dropped and as jet size increased. You feel the car modulate its acceleration as the ignition timing was advanced and pulled accelerating though a high gear due to the ignition air temperature corrections. The data logs show only some of the fluctuations, but not all of them compared to the felt fluctuations. The data rate recorded on the PC is too low.
To confirm, I removed the correction and the feelable effect was gone, but the log stills shows the fluctuations. On a 40C ambient day last summer, there were virtually no fluctuations a served with IATs as has 70C.
The observation of the original poster was that the throttle plate temp vs CC output temperatures dropped as flow increases. This is clearly a indication of evaporation.
At 50C turbo exit temperatures, much of the water and part of the methanol are likely still in the liquid phase, the charge cooler condenses the stuff further.
This big droplets collide with the wall at any bend or any obstacle, and cool is via evaporation. Unfortunalty, due to this effect, little of the spray arrives in the cylinder and mist.
During a rebuild with direct port jets on top of u-turn plenum runners. I could see the traces of the water stream on the front part of the combustion chamber and piston tops. These areas were light brown vs black.
Since moving the direct port jets on top of the plenum, but right behind the fuel injectors in the flat section, I needed to add more ignition advance. A clear sign that more mix effectively arrived in the combustion chamber as mist and not a fluid stream.
Once someone goes to significantly higher boost levels, the corresponding turbo exit temps of well above 100C or even 150C will evaporate much more fluid thrown at it. Riceracers setup is a good example. Condensation in the chagre cooler will still be present, but to a lesser degree.
Overall my little 0.3mm jet used now drops the IATs a tad, but the main work is done by now 4x 0.4mm c-type (150 ml/min) direct port jets.
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Thanks for your info and detailed testing Rotrex.
My setup is currently running with 350cc PRE-Turbo jet and 350cc Post-Turbo jet without intercooler pushing 1.4Bar with a GT28 in a 1.5L engine.
Using 50/50 Water/Meth mix in an ambient temp of 20DegC injecting at 2psi gradually full injection 700cc at 10psi was able to get Maximum temps of High40DegC @ High6Krpm @ 1.4Bar (21psi) reducing drastically till 15DegC during engine braking.
From experience till now, the more fluid I feed it, the more ignition timing the engine wanted, the more power/torque accelaration it felt.
Currently using 4x330cc = 1320cc rated at 43.5psi.
Pressing 59psi Fuel Pressure @ 0psi = 384cc x 4 = 1536cc
Pressing 59psi Fuel Pressure + 21 Boost Presure = 448cc x 4 = 1792cc
Injector duty @ 21psi is about 65% = 1165cc
700cc Water_Meth (DIV by) 1165cc Fuel X (100%) = 60% = 6:10 Ratio Water/Meth - Fuel