Injecting prior to turbo comp' impellers

[SaabTuner]

I think a potentially easier idea (for a mass produced unit) would be two PTC resistors (change resistance based on temp, artificially heated, used in GM MAF sensors) ...

Put on a few inches before the WI, and one a few inches after ... when the resistance values are equal a light could come on, and the ECU could be informed that no WI was taking so that it would use a more conservative map.

Adrian~

[hotrod]

I agree for a mass produced unit something like that would be the best. I need to get the gauge to do some testing.

The only issue I see with temp sensor safety systems is the natural hysteresis time delay in reaction.

Suppose you had a logic circuit that gave a 1 ( WI okay) when the delta T > 20 deg F between the upstream and down stream sensor. It would give a 0 ( WI alarm) when the delta T was <= 20 deg F.

Set that up so if you sense power to the spray relay, and get a logic 1 then use the high boost map. If power to the spray relay and get logic 0 drop to a safe map and set a Check W I light.

possible situations:

A --- first use of WI in some period of time. both sensors stabilized at IAT (intake air temp). The down stream sensor would begin to cool very rapidly but there would be a small but finite delay in its temperature drop. So you would want a small wait interval following start of injection before the CWI light circuit checked for delta T between the sensors.

B --- WI in use, sensors stabilized at max delta T between up stream and down stream. How often does the CWI logic check the temps ( every 1/2 second ??)

C --- Sudden total failure of WI, down stream sensor stabilized at max delta T when WI fails. I see two issues. First if the sensor surface is well wetted with WI fluid, there will be a small period where its temperature will hold low due to evaporation of this fluid film and any fluid that drips from the nozzle ( ie partially blocked nozzle or surface wetting of interior of intake path). Second, if flow is not completely blocked but only impaired you would still see cooling but the amount would drop.

Looking at above there would need to be some tests to determine the ideal spacing between the temp sensors to get best detection of WI failure with minimum time delay, and minimum surface wetting of sensor surface to reduce detection errors.


Another possibility would be to use an IR diode detector pair that looks across the intake path down stream of the spray nozzle. There should be a very significant reduction / scattering of the IR light off the mist. If you have one detector in direct line with the emitter its sensed output should drop dramatically when the mist plume passed between the detector and emitter. If you also placed a second detector at right angles, or even in line on the same side as the emitter beam it would only see scatter if the mist plume was present due to back scatter off the mist dropplets.

You might also be able to detect the presence of the mist plume with a capacitance system that would detect the change in the capacitance between two plates on opposite sides of the intake path. Or a similar inductance system that detected the change in inductance of a coil surrounding the intake path when the plume was present.

A third possiblity would be a charge transfer sensor. Place a voltage potential on the injection nozzle, and a collector screen down stream in the mist plume. You should get some small electrical current transfer in the mist dropplets from the nozzle to the collector screen. This charge transfer should vary directly in proportion to the mass volume of spray dropplets that impact the collector screen.

I think a combination of a 2 or 3 way detector composed of the delta T photo optical back scatter or intake air capacitance/inductance , and charge transfere detectors would be the most fool proof.

It would just require some testing to see the range in detection values and possible false alarm potential for each system.

Okay Saabtuner and I have discribed 5-6 workable detection concepts, all you experimental electronics types, --- go build some prototypes and see if any of these work well enough to use. :twisted:

Larry

[hotrod]

Richard:

Perhaps, the last couple posts belong over in the WI safety discussion, or I could double post it over there if you prefer, because there is some value to seeing these discussions in context as they were developed.

Just a thought --- Saabtuner -- what do you think?

Larry

[SaabTuner]

I agree. Some of the posts should be moved as they are more safety related than pre-comp related.

The problem with the sensor being wetted is moot, it is heated to 220C above ambient to prevent this already. The amount of current needed to maintain that temperature determines the mass-flow through the system.

Even if it were wetted, so too would the rest of your induction be. Therefore the WI effect would taper off slowly. Which is exactly what was seen in that dissertation I posted from Linkoping on WI.

Since these are resistors, and very accurate ones at that, all you really need to do is this:

1. Have the sensors active at all times, but passive.

2. Have a boost pressure solenoid that activates the safety circuit just as your WI comes (at a fixed boost pressure) on and deactivates as it goes off.

3. Have the first PTC resistor (RH) heated to 220C above ambient. (Ambient temp is measured by a third special PTC resistor (RC)) The amount of voltage required to keep that sensor at that temperature differential will depend on the mass flow of the air across the (RH) sensor.

4. Have a third resistor post-WI "wet" (RH) which is heated to 220C above the temp of the special resistor (RC), and if the value is equal, or near to, your "dry" PTC (RH) resistor the power to your boost solenoid should be cut (thus limiting you to base boost, which should be knock free) ...

5. If the voltage required to maintain the second "wet" (RH) PTC resistor increases significantly while the safety system is active (step 2), which means the power required to keep it hot has dropped, power should be cut to the boost solenoid. The level of drop which causes this should be adjustable becuase the WI may not produce a 100% constant cooling effect.

Make sense? Should be relatively simple to setup with the right tools and electronics knowledge. The parts could be scavengened from any GM Mass AirFlow sensor. (Each contains two PTC (RH) resistors and another PTC (RC) resistor.) Pricing is in the $200 though.

If your car is injecting pre-turbo and already has a MAF sensor, you'd just need a second MAF sensor. The value of the second one should just be significantly higher.

Adrian~

[dsmtuned]

Thanks to everyone for your input in this informative and idea inspiring thread!

I am wondering how colder ambient air temps would affect the evaporation of pre-compressor water/ETOH droplets. Hotrod and I live in Colorado and can experience cold winters. Larry, have you had any experience with your pre-comp injection in the winter time? I just wonder if the water mixture would have more of a chance of not evaporating fully and possibly damaging compressor blades.


Another thought relating to the idea of increased air mass and O2 content with pre-comp WI. Some posts here have suggested that the increased air mass due to colder/denser air would not have more O2 content because more air is not actually entering the system through the intake. Wouldn't the O2 content of the air be increased with the addition of WI prior to the turbo because H2O and methanol themselves contain O2? I thought this was one reason for using methanol injected after the turbo because it has a high O2 content (in addition to it's knock suppression qualities). What happens at the molecular level to the O2 in the water and/or methanol at the time of evaporation?


-Craig

[hotrod]

I usually shut off my WI when temps get below about 55 deg F. I simply don't need it for knock supression at those temps with my current set up, and it makes the mixture too cold -- leads to compressor surge problems on my setup in cold temps.



The oxygen in the water is not available for combustion so you can ignore it. The methanol does reduce the oxygen demand slightly as it consumes less oxygen as it burns than an equivalent weight of gasoline.

The colder intake air mass flow does increase the amount of oxygen available to burn simply due to its increased density, but the percent oxygen in the intake air is essentially unchanged from normal atmospheric 21% O2. You can ignore the very small dilution effect of the extra water vapor.


For example if you have dry air (0% RH) at sea level pressure, 59.9 deg F and 29.9 in/hg air pressure and call that 100% air density, if you bring it up to 100% humidity, the density is now 99.35%.

The effect on engine power from humidity change is quite small. If you take an engine with intake air temp of 102 deg F, 0% RH, and absolute air pressure of 29.9 in/hg and call that 100% engine power. If you changed only the relative humidity of the intake air the engine should make 92% of its rated power. The dyno correcton factor for that humidy change would be 1.087.

Okay you lost 8.7% power, but if you now look at the temperature drop effect of Water injection on power output, and drop the intake air temp to 62 deg F. you get your power back. This would be due to the cooling effect of the water evaporation in the intake tract, you now get an engine power output of 102.2%. So you have a net gain in power of 2.2% in spite of the dilution effects of the water thanks to its intake cooling.

Obviously in the real world you'd never start at 0% humidity, but on the same token most of us get extra evaporative cooling from the methanol in the WI mix. The example does show that even in a worst case condition you get more back than you loose.

This is totally ignoring the advantages you get on a boosted engine with increased detonation threshold and being able to crank up the boost.

If you want to play with some numbers and read a fascinating web page on atmospheric pressure effects on engine power check out:

http://wahiduddin.net/calc/calc_hp.htm

Follow the links he has a TON of information on his web site.
In fact we probably should invite him to participate in this discussion.
I'm going to send him an email and see if he'd like to join in on this thread.



Larry

[slowMX5]

Originally Posted by Richard L

Slow MX5 has now all the tools to do whatever you consider to be a real-life test on the theory, must need some careful planning how to set it up properly so that the results can be analysed. It is so lucky thart he has data logging controller.

Do you think a temperature probe is a good addition?

As Richard says I now have a HSV sitting in my garage. I hope to install the HSV and run the wires to control it with a second GPO this weekend - which means that I will be in position to start experimenting next week (assuming I have dry roads for power tuning and WOT data logging). This will provide me with 2 HSVs, independantly mapped, one supplying water post IC and the other supplying water pre-compressor.
So the questions are:
- where to install the pre-compressor nozzle?
- how much water to map to the pre-compressor nozzle (and when to switch water on)?
- what combinations of injection should I try (post IC water off, pre-compressor on etc)?
- anything else?

I have full data logging ability as well, so checking for improved spoolup during say a 5th gear low rpm roll on can be done as well, and I should be able to supply other data that may be of interest.

So guidance and suggestions will be appreciated. My car can be seen at the sites below to help with deciding where to site the pre-compressor nozzle (how about pushing the 4mm ID nylon line through the rubber end of the filter? (doesn't leave holes behind in my intake piping!).

BTW I'm injecting a 20/80 methanol/water mix

Steve.

[Richard L]

I am surprised that there is so far no offers to your questions.

A long thread on theory and the some practical answers could be just a few posts ahead.

I guess you will have to go alone and place the jet in front of the turbo. I would try a 0.5mm jet first (pre compressor) and plot the result against a 0.5mm jet (post compressor) and post IC with the same jet. The logged data can be compared.

What do you think?

[hotrod]

Sorry for the delay getting back to the board, just started a new job but on 12 hour midnight shifts so --------- Argggg --- its friday.


Lets see:

- where to install the pre-compressor nozzle?

My nozzle is positioned about 20 inches so if you can I'd suggest about 0.5 meters for your setup.

- how much water to map to the pre-compressor nozzle (and when to switch water on)?

Start with about 2% of max air flow mass, that will give you near the ideal 3% or so at peak torque rpms. I'd turn it on about 50% - 70% of max boost. If you turn it on too early it can send the compressor into surge, If it operates close to the surge line at mid range rpms just as it comes on boost. Low air flow, but fairly high boost, places the knee of the air flow plot at its closest approach to the surge line on many turbos. I'm getting into surge on my new turbo and may need to install an rpm window switch so the pre-compressor WI can't come on until I get over a certain rpm.

Summit racing has a cheap rpm switch that I'm looking at.

- what combinations of injection should I try (post IC water off, pre-compressor on etc)?

For documentation I'd like to see the Pre-turbo only values, then numbers for both pre-turbo and post IC. I suspect you will want to delay turn on of the post IC injection until you reach the boost level that begins to stress the Intercooler and increase manifold air temps.

- anything else?

Yes, a couple passes with the pre-compressor injection on with pure water, and the common 50/50 mix would be nice if you can. That would give 3 reference points so we could guess-ti-mate what other injection mixes would give.

I'd throw out a pre-test guess of around 25 - 30 deg F drop on water alone and around 40-50 deg F drop on 50/50 mix.


Looking forward to your numbers.

Oh almost forgot, please record ambient temp and humidity conditions if you can.

Larry

[Richard L]

Does anyone agree that having two identical jets, one before and one after the impeller should give a very good indication of how the two work.

Once the data are logged, it will be nice to compare the results.