Tuning W/I via Humidity Sensors

[parmas]

Hello All,

I am trying to find which is the best method to know exactly when enough is enough.

We all should know that injecting extra water more than it "should", would cause the Air Temperature to increase dramatically due to loosing the liquid to gas effect.

This point is called the DEW point where the air could not hold any more water cause 100% relative humidity has been reached. Above this point the effect is not produced anymore but instead water now being formed around the intake plenum and pipes due to condensation.

Now I was thinking that if a Humidity sensor/transducer is installed into the plenum, the tuner could understand how much humidity is actually under going when water is being injected thus being able to stop at about less than 95% humidity to be safe.

What do the experts think about this idea?

[parmas]

Here is some juice to drink :

Water Injection theory & Defintions : http://en.wikipedia.org/wiki/Psychrometrics

What is WET Bulb Temperature : http://en.wikipedia.org/wiki/Wet-bulb_temperature

Relative Humidity Info : http://en.wikipedia.org/wiki/Relative_humidity

Evaporative Cooling, the effect of Water injection : http://en.wikipedia.org/wiki/Evapora...cal_principles

Info on DEW point : http://en.wikipedia.org/wiki/Dew_point

Psychrometric Chart : The practical elements plotted on a graph. This graphs shows you one of the most important things of water injection. The less humidity, the more is the cooling effect difference between the Dry-Bulb (Ambient) Temperature and the Wet-Bulb Temp.

Understanding the Psychrometric Chart : http://www.swst.org/meetings/AM05/peralta.pdf

[Flr Power]

It is useless to tune WI via an humidity sensor since you need excess water in the combustion chamber where most of the work is done...

[parmas]

Originally Posted by Flr Power

It is useless to tune WI via an humidity sensor since you need excess water in the combustion chamber where most of the work is done...

I didn't understood your theory. Please explain

[Flr Power]

Not mine but rather 1940's theory!

[parmas]

Originally Posted by Flr Power

It is useless to tune WI via an humidity sensor since you need excess water in the combustion chamber where most of the work is done...

You need to define the terms "excess water". At some point of excess you are mentioning the water injected will actually be blowing off the spark, reducing power stroke due to unburn fuel and less oxygen due to Air filled with water.

More excess than that and you will blow piston rings and head gasket or hydrolock.

My theory of using humidity sensor is to be able to achieve the maximum water injection benefit without causing the above effects. I mainly use water injection to cool the intake air to prevent detonation at higher boost pressures.

Above the so called DEW point you will not cool any more air as it is already 100% filled with water.
At this state the more you increase water injection the more air you will displace due to excess of water into the system.

Less air = Less power = Pointless excess !

[Flr Power]

Using the minimum of WI to just cool the intake air is alright. My point is that you would normally need to inject way past the dew point to have enough detonation protection.

If you can get away by using the minimum amount of WI to just cool the intake air, it means the engine is not pushing serious amount of power (per liter) or you are running alcohol fuel.

[parmas]

Originally Posted by Flr Power

Using the minimum of WI to just cool the intake air is alright. My point is that you would normally need to inject way past the dew point to have enough detonation protection.

If you can get away by using the minimum amount of WI to just cool the intake air, it means the engine is not pushing serious amount of power (per liter) or you are running alcohol fuel.

I think we are not understanding each other.

When I installed the water injection system never had the thought to inject water into the chamber or at least not enough like you are saying.

If I was making "serious power" I would never inject more water to control the burn but rather retard ignition timing or increase fuel mixture.

Over-injecting water would preserve an engine if it is making "serious power" by reducing/slowing the burn due to a cooler burn plus less air is into the chamber due to now water is instead of air in which it is equals to less power stroke = less "serious power".

Hot Air Temps are the actual danger of forced engines being prone to pre-ignition / un-controlled burn or detonation/knock and that is what water injection should be used for .....nothing else.


Summary :

- Injecting water till dew point into the intake will get you the coolest air that you can achieve.

- OVER-injecting water over the dew point will actually displace air reducing engine air flow. Less air-flow = Less power due to richer mixture

- Over-injecting water would make water condense into the plenum / throttle body etc.. which would be liable to corrosion or even hydrolock if there is excess water formation.

- If Water injected is controlled till Dew point and the Air temps are still high for your tastes (above 40DegC) you need to :

1. Check what is the efficiency of the turbocharger and try to set the ecu to target these efficiencies at various rpms

2. Decrease intake temp by either Air filter position or else pre-turbo water injection

3. If these are not enough, consider using a bigger pump pressure so that water is sprayed finer. The finer the water mist the more difficult to reach dew point = chance of cooler air.

4. If also with big pressure is not good than consider intercooling before water injection but this will cost you spool up time and a laggy engine = to less torque on low to midrange rpms.


Presently my setup is a 1.5L engine running a GT2560R turbo - NON-intercooled @ 16psi and 20DegC Air Temp seeing 35DegC Air Temp.
Next Pre-Turbo water injection to reach target of 25DegC Air Temp.

[rotrex]

Point is that the water mainly acts in the chamber or to a degree the compressor.
It needs heat to evaporate. Lots of it. as the the droplets cool down due to evaporation and the water's vapor pressure is rather low and drops with temp, water does not evaporate fast unless you provide lots of HEAT.

This is static effects (heat of evaporation) vs. dynamic effects (heat capacity, vapor pressure vs. temperature).

Intake air cooling in the pipes is a minor effect. Folks have tried that for decades.
the temp readings barely change.

issues like water replacing air reducing power is akin to "running rich costs power as it replaces air". It is a minor downside compared to be able to run at MUCH higher boost than without and/or getting higher cylinder pressures from more ignition advance. -> more power.
You lose a few percent of potential power and gain several times that as real power.
A turbo increases backpressure, hence costs power. As you know, that is only half the story.

shoving the maximum amount of fuel and air into an engine is only one part of the story making power. You also need to be able to extract this energy and convert it into mechanical power. This needs optimum ignition timing to achieve max. cylinder pressures at the right point in time.


What you try with humidity sensors and some cooling is like trying a different cone air filter brand to gain more power. The effects are negligible compared to water or w/m in the chambers.
You ignition will have no issues unless you flow massive amounts of water.
In my engine this was at about 600cc/min pure water. Adding a tad of dwell time in the ECU in the area of the map fixed even that.

If you use methanol in your mix or pure methanol, that all changes.
Methanol has a lower vapor pressure and lower heat capacity. it evaporates much faster given the same temperature environment is provided compared to water.
Energy per time unit is cooling power. As more methanol evaporates per time unit compared to water, it tends to cool the air more in a intake path. In the chamber itself or in the turbine, the difference is of less importance as these places are a much hotter environment.

The chamber is water or methanol flow limited in most cases regarding how much they can evaporate and how much cooling you can achieve.
More fluid= lower air temp in cylinder (where it counts the most) = more power.
Of course there is a limit for a given IAT and compression ratio. At some point, it will flow out of the exhaust. The WW2 engineers tried that, too.
If you stick to the here recommended 10-20% water to fuel ration, this is of no issues. If your boost goes above 25 or even 30 PSI, you can add much more.
See RICERACERs RX7 development. His engine works in the same extreme regime as did the WW2 aircraft engines. The more w/m he adds, the more boost he can run and the more power he gets from the engine.
In his high boost setup with pre compressor injection, the IAT reduction is much more pronounced and an important element to gain big HP numbers.

you can take w/m to the extreme. Just add more boost and more fluid.
You are essentially only limited by the mechanical strength of your engine. 100PSI boost in a 1.5l 4-pot. That's what BMW and others did in the 80s F1 engines getting 1000+HP.

The boost pipes are energy limited when it comes to water evaporation. There is not enough heat to evaporate all the water. The droplets plainly become too cold to further evaporate. This is actually nice, because now they can make it where you really want to have them, in your engine.

the aquamist system in the WRC cars worked so well with pure water because the turbos were used at insanely high pressure ratios producing extremely hot charge. This was caused by the intake restrictors required.
And even they used direct port injection. They did not care about cooling in the pipes. They (and we) cared about cooling the charge in the cylinders. Even more specifically, you care about cooling unburned charge in general and eve more in the area of pressure or shock waves while the flame front advances to prevent spontaneous ignition aka knock. Shock waves compress the charge heating it further. Droplets evaporate faster, cool the mix and by that reduce the pressure. It dampens pressure waves. It also slows heat up at the flame front. Thats why it slows flame speed.

The music plays in the cylinder. It is just not that easy to get it there in a uniform way. This is where all the discussions from nozzle location come from. It is a lot about practicality vs. complexity.



The turbine can also evaporate a lot, if pressure rations are high or efficiency low.

If you use plain water, try a intercooler or charge cooler first.
Your cooling to the due point is not worth the trouble.

I have used a Rotrex C30-74, now replaced by a C30-94, with various nozzle locations and mixes.
non-intercooled I saw 100C IAT with 0.6bar of boost. just look at your compressor maps and do the math.

Injecting water does very very little to change the IATs. Maybe 20C.
Injecting methanol before or after the compressor has more dramatic cooling effects. The most extreme for me was 300cc/min 50:50 water methanol pre-compressor injection. I saw IATs actually dropping to ambient temps as boost was climbing.

I cannot see you getting only a 10C increase in IAT over ambient at 1 bar of boost without charge cooling and only minor post compressor water injection at 200g/sec of airflow.
There is something wrong or missing.


Once you use serious amounts of water that actually makes it into the combustion chamber, droplets do not like to take tight turns e.g. in a plenum with bend runners, all those factors like humidity and even intake air temp become of less importance.
See it as your cell phone playing music in the first row of a rock concert. it will make no difference to the audience.

If you want to make significantly more HP from your setup, especially without charge cooling, you need to get the water into the chambers, lean out the mix 12-13:1 and advance the ignition close to best torque or the knock limit.
if you hit the knock limit first, add more water/meth and further advance the ignition.

In the end, I now use direct port injection with 4 75ml/min nozzles 2" before the fuel injectors. Fuel i complimented by 4x 440cc/min injectors.

For the ignition, I am still knock limited, I found that up to about 60C, IAT plays little role to ignition timing. I only pull serious timing past 70C. Before that it runs really well with a particular aggressive sound.

Ignition timing at peak torque is about 23? without WI and 29? with WI, both at 0.7 bar and 6500 rpm. Engine a build 1.8l Rover K with a 8.5:1 CR in a Lotus Elise.

Mapping the same engine without WI, I can't remotely achieve similar power levels.
The engine is charge cooled, but the pre-rad is currently too small. That does not help.
A new engine radiator sized pre rad is already sitting in my basement, but the car is away in winter storage until March.
Together with bigger lines and a bigger pump, IATs will drop.
This will allow me to extract more power without WI, but also with. The gains are just lower.

Try adding more water/meth and map for it. You will be surprised how well it works.

Pure water in my experience leads to rather slow (initial) burn speed requiring you to use a lot of ignition advance. This is harder to tune.
Adding 50% (wt) methanol compensates that to a degree and makes it easier to tune. The slope of ignition advance vs. power gain is more steady with a smoother transition to knock in my engine.
At least it does for a low to medium boost engine.
Once things are really hot in a 30+PSI engine, this is less of an issue.

[Flr Power]

Well said rotrex. This is what I was trying to tell parmas.

Rotrex, one thing I do not understand is that you said "For the ignition, I am still knock limited". Do you mean your engine is knock limited because you are not spraying enough w/m ?