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Old 24-09-2004, 06:44 PM
b_boy b_boy is offline
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Default Tuning for water injection: fuel, ignition, and EGT

I'm starting this thread in the hopes of developing a Tuning Guide that could be a Sticky in this Forum.

Folklore has it that for now EGT is the best method of monitering the tuning with water injection. For us novices, some understanding of a tuning "algorithm" would be of benefit. I'm going to start with a straw-man approach, posing a method to use as framework for further development.

1) Tune the car for power without WI, no knock.
2) WI turns on at 3-5 psi boost.
3) Add water injection in the 10-25% range (ramping with boost is good).
4) Remove fuel until (an unobserved, but inferred) 12.5 AFR is reached, watching EGT.
5) EGTs should not rise above pre-WI temperature.
6) Advance ignition until knock is detected, watching EGT again.
7) If 12.5 AFR cannot be reached without knock or high EGT, stop reducing fuel.
8) Advance ignition or add more fuel to reach optimal power even at sub 12.5 AFR.

The parenthetical comment 'unobserved, but inferred' comes from the idea that with water injection on the oxygen sensor cannot be trusted. One may however subtract fuel until the ratio has reach 12.5 by simple subtraction of a percentage (e.g AFR 10:1 --> 12.5:1, subtract 25% of fuel at 10:1).

Now one thing I've notice in the various "calculators" I've browsed is that more power can be had with lower AFR than 12.5. While this is the fuel ratio of optimal power per gram of fuel, it may not in practice be the AFR of best power. So, I question the assertion that 12.5 AFR should necessarily be the starting goal for best power.

Also ignition advance is a moving target. The peak torque achieved during a combustion cycle varies across the RPM and load range (by only a few degrees probably). At some point more advance will become detrimental to power and especially at high RPM when valve timing will necessitate decreased advance.

None the less, in my steps 1-8 above, I have taken as a given that 12.5 AFR is the number to shoot for, and that ignition advance is used to achieve optimal torque once the "optimal" AFR has been reached.
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Old 24-09-2004, 08:26 PM
Richard L Richard L is offline
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This is a going to be a good thread. Tuning with water inejction is the least talked about topic. I will sticky it as soon as it gathers pace.

The steps listed is a very logical approach to the subject.
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Old 24-09-2004, 11:01 PM
dsmtuned dsmtuned is offline
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That sounds like a pretty good start to me! Of course, every car is going to be a little different.

For my DSM, I tune for knock and not EGTs so much. My car can have knock that can be tuned out without ever having significant changes in the EGTs. Of course 'if' the WI is turned off, the EGTs go through the roof!

I think another good thing to mention is trying different mixtures of Methanol and distilled water. I have found that I am able to lean out my fuel without knocking a bit more when I run less than 50% methanol. Maybe like 40/60 meth/water. I think this is because my knock is mostly a result of heat soak of the intercooler and so I need more water to do more cooling.

That's all I have, for now.

-Craig
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Old 25-09-2004, 05:16 AM
mx5 mx5 is offline
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My setup -> 2D kit, 0.5mm + 0.6mm dual nozzle setup, up to about 350 cc/min water injected (currently distilled water only, no alcohol) at redline 7500rpm. Water is about 25%-30% of fuel, injected pre blower (non intercooled Eaton M45 spun to 16K rpm). I am running 10 psi boost, water injections starts at 3 psi.

On the dyno for the final tune of my MX-5 we were tuning for 12.8:1 AFR (it did the max power there) indicated on my TechEdge WBO2 wideband with the water injection on just like with the water injection off.

I didn't notice the injected water (water 28%-30% of fuel) changing the wideband AFR readings

These talks of 12.5 AFR being indicated as 10:1 on the wideband O2 seem being bogus!

The EGT sensor is in one of the exhaust runners - as close to the head as possible (about 1 inch from the head).

My EGT were around 1200F (~ 650C) at 10 psi, 7500 engine rpm.

The intake air temperature sensor is in the intake manifold just in front of the runner of one on the cylinders (it measures the temperature of the air just before mixing with the fuel).

The intake air temperature at cruising on the dyno was 130F (~ 55C).

With water injection turned off at 10 psi of boost the air temperature was raising under boost to over 260F (over 130C).

With the water injection on the intake temperature raised only to 160F (~ 71C)

The ignition timing at 10 psi boost/7500 rpm was about 25-26 degrees advance

My power went up from 100 hp at the wheels (the stock power of a '94 Miata) to 190 hp at the wheels with the current setup (stock engine, never opened, 104K miles on it).

I am going racing this weekend Time to hug some curves

Next step is probably putting bigger water jets and increasing the water flow (probably above 30% water of fuel)


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Old 25-09-2004, 07:38 AM
JohnA JohnA is offline
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Default Re: Tuning for water injection: fuel, ignition, and EGT

couple of thoughts here :smile:
Quote:
Originally Posted by b_boy
..Folklore has it that for now EGT is the best method of monitering the tuning with water injection.
It's an important tool when you're tuning on the edge - but I wouldn't go as far as stating 'the best method'

Quote:
2) WI turns on at 3-5 psi boost.
Where did this come from? :shock:
That would only be true for non-intercooled engines mate, or else it's FAR too low
Quote:
3) Add water injection in the 10-25% range (ramping with boost is good).
on well intercooled engines, over 10% could bog it down. Where did the 25% come from?
Quote:
8) Advance ignition or add more fuel to reach optimal power even at sub 12.5 AFR
I've seen max power at around 14:1 with W.I., so we'd need to verify with others that the 12.5 figure stands in this case
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  #6  
Old 25-09-2004, 07:49 PM
hotrod hotrod is offline
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Default Some observations

On turbocharged cars you want heat in the exhaust to get good spool up. In fact, some turners intentionally run lean AFR's at low boost to enhance the spool up of laggy large turbos. I would suggest the turn on point be as late as practical for that reason on turbocharged cars.

I would suggest you set the turn on point just a bit below the boost that under high load (with a given fuel) just begins to show mid-range rpm knock. Engines will typically knock first at rpm's near the torque peak rpm.

What I would, do is find a good steep hill, fill the gas tank and throw some crap in the back seat and make a series of pulls up the hill after you get your basic tune dialed in. Gradually increase boost until you just see signs of knock on a quality knock monitor like a Knock Link or on reading your plugs for signs of detonation. This becomes you ceiling for operation without WI. Then set your turn on point a bit below that boost setting, so you have a little cushion for extreme condions and any delays in the spray actually getting into the air stream.

(another way to determine your knock limited boost for the WI turn on point, based on high load, would be to intentionally run one grade poorer octane fuel than you typically run. Find the first knock limited boost point with that fuel, and set your WI turn on point at that boost level so you would be safe on a poor fuel grade one step lower in octane than you normally use)

Keep in mind your knock point will be lower in hot temps and on long duration high gear pulls, where you spend more time at high load. This is one reason dyno tunes frequently kill engines that are never double checked with a road tune. Unless the dyno can hold a load at a set rpm you can never see peak cylinder temps during a quick pull through the rpm range on most chassis dynos.


As far as timing, the folks at NACA always did their tests at MBT (Minimum Best Torque) timing. They did that by tuning for maximum torque than backing off the timing until torque dropped 1%. That guarantees your on the safe end of the torque/timing plateau. For example on a 400 ft/lb torque engine, you give up 4 ft/lbs of torque for a very large measure of safety.

As mentioned above the tuning for WI is not a single pass process but rather an iterative multi step process.

With that said, I would tune for best power without WI, and find your MBT timing under that condition. This should change very little as you add WI.

Find your best/latest safe turn on boost point.

The old school approach used by the Buick GN folks then involved an iterative process of adding water until the engine lost power, then add boost, or leaned fuel until it "wakes back up", then keep repeating that cycle until you learn what your engines tolerance level is. Usually by watching EGT's and knock indications.

All the NACA studies indicate that max power always occurs with WI at AFR mixtures leaner than max power without WI. WI at AFR richer than about 11:1 are a waste of time, as your drowning the engine in fuel and water. The ideal lean AFR will change with WI rate and mixture.

I would be slow to move away from the MBT timing, as over advanced timing can create huge cylinder pressures, with small net gains in power.

I would deal with timing as the last careful tweak to the step wise tuning process. As mentioned above your WI mixture will modify your burn speed and that in turn will slightly modify your MBT timing. So every so often you would double check to see your still near MBT, then go back to tuning via AFR, boost and WI mix.

It is interesting to note that engines of similar design, frequently cluster around a very small range of ideal ignition timings. To the point that many tuners believe you can get a given high performance engine family (say a small block chevy) very close to max performance with a widely recognized timing recipe.

Larry
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Old 27-09-2004, 07:51 AM
b_boy b_boy is offline
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HotRod (Larry) states the following:

As mentioned above the tuning for WI is not a single pass process but rather an iterative multi step process.

With that said, I would tune for best power without WI, and find your MBT timing under that condition. This should change very little as you add WI.

Find your best/latest safe turn on boost point.


I agree it's iterative as is most tuning. One question for me is: should the iteration be adjustment of the amount of water or the fuel. This brings me to the question of how much water to inject in general. There are all sorts of opinions in this area, most of which are stated with conviction.

How much water to inject

From what I've read less water is needed at low RPM under load, and the need for water increases with RPM. The same is true with boost, as boost increases (and consequently heat, abdiatic heat) so does the need for water. Makes sense.

Richard Lamb has an interesting graph of water requirement that can be seen in the Forced Induction thread: "Driving Aquamist 2c high speed valve with stand alone EMS."

Water is injected based on boost, RPM. I assume, as I think other's did in that thread that these parameters are fairly universal (hence the MF2). How the proportions on this graph are interpreted is important, but once a maximum rate is determined, ther remaining values are just relative to the maximum. The maximum injection rate is typically 10-25% of the fuel injection amount.

To begin tuning, I think a 15-20% maximum would be a good starting point. More can be injected if maximum brake torque (MBT) cannot be achieved with ignition timing.

Tuning for power with or without WI, will be targeted toward MBT. For a given engine, as Larry states, the MBT will be fairly consistent (cluster) in terms of ignition advance. An engine's MBT will differ according to its stroke length. MBT occurs near or at a point of greatest leverage on the crank when cylinder pressure does the most work. The speed with which the fuel burns will have impact on when ignition spark advance reaches maximum torque. I agree the MBT can and should be determined with WI off. With WI on, the ignition advance may be further advanced due a slower burning of the fuel.

Water Injection Point

The consensus would seem to be turn the water on as late as possible, which is sometime after boost onset, and prior to the onset of knock. This point will have to be determined empirically.

Knock onset, would be measured with ignition advance in the MBT range. In other words, pulling advance to suppress knock is counterproductive when tuning for power.

Air to Fuel Ratio

In Ed's paper (Charged Performance) he has a great graph that indicates that best fuel economy occurs an AFR or 14.5:1 and best power occurs at 12.5:1. Leaning or richening the mix above or below 12.5 leads to less power.

Please chime in on this. I've never seen someone lean out to 12.5 for maximum power. While maximum power per unit fuel may occur at 12.5:1, the maximum engine HP power may occur with a richer mixture of say 11.5 or 11:1.

O2 sensors
I have only heard that WI fouls up O2 sensor readings. By how much, I do not know. EGT has been held up as a means of tuning when O2 sensor readings are not reliably known. One way that I have heard of this working is to add WI, and let EGTs fall. Fuel is then subtracted, and the EGT's rise. Fuel is removed until EGTs reach their pre-WI level.

In reality, I imagine the O2 sensor readings are not very far off. Water is a byproduct of combustion, but not to the levels normally seen with WI. Partial pressure of water may or may not interfere with O2 detection.

Trimming WI
While starting with 15%-20% maximum maybe enough to get a good tune. Thinning the water out preserves your supply and extra water may lead to less power (bogging). I don't know how to determine when "enough" water has been injected, especially when I'm injecting post-IC and just prior to the throttle body--and no sensor, but power travels with the water past that point.

As far as I know there is a wide range of water that will produce good or best power, so trimming water back may not be a big concern.
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Old 28-09-2004, 08:34 AM
Richard L Richard L is offline
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Keeping the same format by b_boy, I like to add a few a little to each section for simplicity.

How much water to inject
Rather quoting a general figure of w/f ratio, it would be a good opportunity to look more deeper into the reason behind the suggestion. I have always lean on the side of using water injection as an in-cylinder coolant because the other alternatives are excess fuel. It is also quite simple to calculate the quantity need to perform such an task. Other cooling tasks such as inlet charge cooling is not as simple to calculate due to many variables. I hope we will reveal the way it can be calculated (it has already been mentioned in several threads), hope it wil be repeated on this section by previous contributors.

May be there is a thermodynamicist here would produce a model of how water react during the journey from injection point to exiting the exhaust pipe. Any offers?

Heat exchanging model per gram of water:
inlet cooling => induction stroke cooling => combustion stroke cooling => exiting the exhaust pipe.
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Old 28-09-2004, 06:20 PM
SaabTuner SaabTuner is offline
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Firstly I'd like to add that even small amounts of water injection significantly change MBT.

Now for the justification.

This stuff is all from the PDF document I submitted here several times which covers Ionization Gap Sensing in combination with feedback ignition timing and PPP control.

From page 100 of 207:

"Figure 3 A large part of the test cycle is displayed. The spark advance controller is shut off around cycle 100 and advance is held constant. The water spraying starts around cycle 250 which leads to increased PPP and decreased torque output. The spark advance controller is switched on at about cycle 400, controlling PPP back to MBT leading to increased output torque. The water spraying stops around cycle 550 and the parameters asymtotically go back to their initial conditions, when the water still in the system, e.g. deposited on the walls, decreases."

I need to resize this image to fit screen. Admin



Now if I could just rig up my Saabs ECU to do that. ops:

Anyhow, they were spraying a relatively small amount of water, but were running at part throttle, so it may have been a very high water/air ratio.

Nevertheless it should be noted that adding WI effectively moves the Peak Pressure Position (PPP) back about 5 degrees, at least on these experiments.

This is also the largest flaw I saw on the NACA studies. All of their conditions were at MBT without water injection. So of course, when the water moves the PPP back 5 degrees you can run more boost and less fuel. It's just like pulling timing 5 degrees.

Darn that flame development angle. :twisted:



Adrian~
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  #10  
Old 28-09-2004, 08:26 PM
hotrod hotrod is offline
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Default MBT

Quote:
Firstly I'd like to add that even small amounts of water injection significantly change MBT.
I think we are saying the same thing in different ways. Perhaps a difference in interpretation of certain words.

I don't think a 5 degree shift is all that big. I see a 3 -5 degree change in MBT as an expected change that is easily delt with.
That is why I included the following statement to periodically "tweak" the timing slightly.


Quote:
I would deal with timing as the last careful tweak to the step wise tuning process. As mentioned above your WI mixture will modify your burn speed and that in turn will slightly modify your MBT timing. So every so often you would double check to see your still near MBT, then go back to tuning via AFR, boost and WI mix.

In the NACA report E5E18 ( 1945) it shows that the shift in MBT timing is roughly proportional to the amount of ADI fluid injected, and depends to some extent on the mixture ( ie alcohol/water mixes had less need for additional ignition advance that pure water did.) There were also some differences noted depending on the location of the ADI injection point. (probably due to differences in the mass fraction that evaporated pre-intake valve vs in the cylinder)

So your rule of thumb for tuning would be:

As you increase WI rate, you will need to add a small increment of timing from perhaps 2-5 degrees, for each major step in injection rate, (ie going from a 10% to a 20% rate.

In the above NACA study they saw a change in ignition timing for MBT going from 29 deg -to- about 41 deg advance when going from no injection to 1:1 fuel/ADI fluid, when the ADI mix was 50:50 water ethanol.

This test series was run in 1945 where many of the other studies were run from 1938 - 1942 time frame. I understand that the ignition timing was not readily adjusted on many of the aircraft engines, so early studies focused on fixed timing operations.

The important aspect of the issue to me, is that it should be one of the last means used to bring the tune in. Too many people use it as the first thing they modify to solve knock problems.

There are some people that just keep dialing in advance and do not realize the dangers of overadvance in a high performance engine as the cylinder pressures can go orbital with just a couple degrees of excess advance.

Fuel air ratios also effect optimum ignition timing due to changes in burn speed. So by adding WI rate, and leaning the AFR you are introducing opposing effects. In the same study they found spark advance for peak power plots as a bath tub curve ( ie shaped like a large U ) when plotted against fuel air ratio. Minimum advance occured near AFR's of .08 - .095 (12.5:1 -- 10.5:1) with rapid increases in necessary ignition advance either richer or leaner than those mixes. At an AFR of .06 ( 16.6:1) the ignition advance needed was about 14 degrees more than the minimum.

Due to the effects of WI rate, mix and AFR on MBT, you actually have about 4 different ways to change effective ignition timing.


Larry
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