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Old 23-03-2019, 02:29 PM
sambeeb sambeeb is offline
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Location: sydney
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Default boost pressurised pre comp WI


I'm looking to fit a boost pressurised pre compressor water injection setup onto my VW 1.8T which runs the small K03s turbo. The turbo is way outside its efficiency range and so is producing a lot of heat so I wanted to use this system as a way to use wet compression to make the turbo a little more efficient and 'act bigger' and also keep post comp temps down from where they currently are.
Here it is being bench tested @ 1 bar of compressed air as a 'boost source':

and here its being tested to see how the droplets travel through a tube:
I think those droplets will sail through if switched on at about 10psi.

The nozzle is a spraying systems SUE15B. Threads on here seem to suggest that you need to inject water to the tune of 10-15% of total fuel flow.
I have 380cc injectors that are operating at 85% duty cycle when flat out. 85% of (380cc X 4 injectors) = approx. 1292cc of fuel flow max. 10% water of that = 152cc/min, 15% = 228cc/min.

My nozzle runs:
5psi - 1.0 gal/h = 75cc
10psi - 1.4gal/h = 105cc
20psi - 2.0gal/h = 151cc

So with this nozzle it looks like at 20psi (which is the boost peak), i'll be at 151cc which is on the min of the suggested range of water to inject =10%.

So first up, do those calcs look sound?
If correct and given that I am on the lower end of the ideal range for pre comp injection, does it stand to reason that I can also then run another pumped nozzle downstream if need be to achieve a better water:fuel ratio?

Now a hardware question. Not sure if you can see from the short vids, but there is a one way valve on the boost signal line. I'm thinking that when under vacuum that will close preventing the plenum being able draw the reservoir into vacuum OR draw air in reverse through the nozzle representing an air leak. Am I correct in setting it up that way - I don't need a 1 way valve anywhere else?

thanks for any help
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Old 26-03-2019, 09:00 AM
Richard L Richard L is offline
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Default Re: boost pressurised pre comp WI

looks good. Can you make it variable with RPM as well? Once the boost pressure will not increase once it reaches wastegate setting.
Richard L
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Old 27-03-2019, 10:12 AM
sambeeb sambeeb is offline
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Default Re: boost pressurised pre comp WI

My small turbo ramps rapidly up to a 20psi peak at 3200rpm or thereabouts and then boost trails down to about 12psi at max airflow. With boost pressurized I guess it would be possible to modulate water flow against injector duty cycle provided I used a nozzle that could provide enough water at peak air/ fuel flow, but at 12psi. At the boost/torque peak it then wouldn't matter that there was excess boost as the flow would be modulated by the solenoid? But since the fogging nozzle has an air and water signal (both exposed to boost pressure) it stands to reason that I'd need to modulate the flow of water and air to the nozzle equally. Do they make dual circuit/quad port solenoids so that a common solenoid could be used for both signals. I think without controlling the air and water to the nozzle simultaneously the behavior of the nozzle would get a bit unpredictable yeah?

As it is the system I suggested will spray the most water at max boost/ cylinder pressures where my car is normally seen to be pulling bits of timing and then would be under flowing at higher rpm. I guess this would be good for inlet temps at the critical knock point, but would not give the wet compression ' bigger turbo' benefit later in the rev range as I wouldn't be spraying enough water. Yeah I see where you are coming from as what you suggested would produce that benefit too, not just cooling.
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Old 10-06-2019, 08:02 AM
rotrex rotrex is offline
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Default Re: boost pressurised pre comp WI

With so little flow, I would not worry about modulating the flow. Just activated it when you hit some boost level.
In order to really do something, you should try to increase the flowrate significantly to like 25% of the fuel flow. You will need to retune your ignition timing.

I would also install a bigger turbo on that VAG 1.8T. There are plug and play compatible turbos on the market. A T04 sized turbo can easily push you into the 250 to 300HP territory. These engines will take that all day long without any upgrades required.
Just ensure that the coolant is always flowing and the thermostat works properly. If you stall them on a trackday, you may distort the cast iron block.
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